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I bought a charcoal gray couch - love the color in the store. In my living room it looks dark blue! What color should I use on the walls and accessories to make it look gray again?    (answer)

Can fluorescent colors be printed with cymk printing system? I have Roland printer that uses eco-solmax inks. Are there any RGB or CMYK codes that will work?    (answer)

In textile color matching, Is it possible to match target color in all light source without metamerism. If so what will be the possibility percentage?    (answer)

What does a white balance actually do?    (answer)

What makes a color bright?    (answer)

I study the topographic influence on snow. When an individual looks at snow in shadow, they are actually seeing blue light, yet they state they see white. Is this based on learned experience of color? What effect does the question have, i.e. "What color do you see", vs. "What is the color of the snow?"    (answer)

How does a flower´s color help it survive?    (answer)

Many auto accidents happen in early morning and late in the evening when it is dark outside. Does the vehicle color have anything to do with this? What automotive paint color is easiest for the eye to see when it is dark outside? How about in daylight?    (answer)

Although our sun is often depicted in artwork as "yellow", I have heard that it is actually "white", and that is why a white piece of paper appears white. Is this true? If so and we lived in a solar system with a different type of star, such as a red dwarf or a blue giant, would any objects appear "white", or would they take on the cast of their light source?    (answer)

Imagine driving down a street toward a traffic light. How fast would you have to go so that the red light (700 nm) would appear green (500nm)?    (answer)

Is there a way to measure gloss with a spectrophotometer or is it necessary to have a glossmeter? Is there a conversion between CIELAB values and gloss?    (answer)

How can I avoid metamerism?    (answer)

What are L* a* and b*? Are they constants? If not, how can I find those values?    (answer)

Where can I find calculator or software for LRV?    (answer)

We are told that Red, Yellow, and Blue are the "primary" colors, and that you can make all other colors from them, but those 3 can´t be made by combining the others. In additive systems, it is red and green that combine to make yellow. Is there something inherently special about red, yellow, and blue, or are they considered "primary" only in the sense that the most basic medium of color manipulation is a subtractive system?    (answer)

When we compare luminosity of different hues, we find that blue is a relatively dark color, and yellow is a relatively light color. Do hues have an inherent luminosity independent of human perception?    (answer)

I am trying to emulate a smaller-gamut RGB color space on an LCD display using a 3x3 matrix, and I can not seem to figure out the general-purpose way of doing this. You reference Poynton´s book in a similar FAQ but he skips over the process and just spits out the answer for some important cases.    (answer)

Is there is a device that can measure liquid gravure ink spectral transmittance? I need a method to confirm ink recipe components in a liquid ink sample. I could use a faster option than the traditional draw-down proofing method.    (answer)

How many lights are metameric to white light reflected from a paper?    (answer)

I use the Munsell Color Books to develop color harmonies for clients to use on short term projects. Is there an inexpensive way to get swatches or chips that match the Munsell notation? Can I print them?    (answer)

Are there studies of floral arrangement preferences of dichromats?    (answer)

How did the CIE 1931 color matching experiments evaluate the whole gamut when we know that the RGB color gamut is a subset of that of the human eye? In other words, we know there are colors that cannot be matched by the RGB lights. How did they get around this?    (answer)

The sensitivity of the human eye to color difference is greatest at approximately 550 nm. However, in interpreting the MacAdam ellipses , it would appear that humans are least sensitive to differences in color in this region. Why?    (answer)

I measure timber colour using a Minolta Chromameter CR-400. I want to compare my values with those of other woods whose colors are listed in percent Luminance, Dominant wavelength (λ)and percent purity. Can I convert these values over to CIELAB?    (answer)

Is it possible to scientifically determine the original colors in an old black and white stereoview photograph if some of the colors are known?    (answer)

How does aging affect color perception? Are older people able to discriminate brighter colors or softer colors better?    (answer)

What wavelength(s) are used in the calculation of Gardner color?    (answer)

Is it possible to explain color to a blind person if thay have never experienced it? Can the brain of a blind person assign a color to something if they know the shape but not the color?    (answer)

I need to predict CIELAB of a color at different thickness. The color is transparent and .01 inches. How do I predict LAB values at thicknessof .121?    (answer)

Why do different pure hues have differing lightness values?    (answer)

In his 1943 OSA paper "Specification of Small Chromaticity Differences" MacAdam describes constants g11, 2g12, g22 and gives values for them in graphical form. Is there a source for this data in conveniently tabulated form?    (answer)

I need a device that will give me color readings at an observer angle of around 45 degrees or so that will pick up almost 100% specular reflection.    (answer)

Why is it not possible to get an accurate ΔE colour measurement on a metallic powder coating?    (answer)

At what luminance (Candela per meter squared) in the ambient environmental light does scotopic vision turn to mesopic vision, or at what point can we start to see color? And at what point can we see the majority of colors?    (answer)

What is the most common first color that children recognize? The second?    (answer)

We have a WWI aircraft we are recovering with fabric that requires a dark green paint for the wings. This aircraft is flown a lot and displayed to the public outside quite a bit. The problem is that this paint absorbs sunlight heat dramatically which reduces the life of the doped fabric, causing it to shrink prematurely and it is fairly expensive to replace. Would a primer coat of silver dope or white help reduce the absorption of the heat into the fabric under the dark green paint?    (answer)

Do you know the origin of a measurement called the "flop index", which is defined as flop index=2.69(L15°-L110°)^1.11/((L45°)^0.86). My Xrite M68II reports this metric, however, X-Rite does not explain the source of this equation. Do you know where I might find the source of this equation, or another good way to mathematically explain the color difference at several angles?    (answer)

What is the differance between additive color and subtractive color?    (answer)

I am turning my formal dining room into an art gallery. We painted today and it is too bright. The way it looks now all you will see is the paint color and not the art. What are the best colors to paint a gallery, given that all the pictures are of different color schemes?    (answer)

Scientifically speaking, is black a color? Is white a color?    (answer)

In comparing light bulbs based on their color temperature, how much difference in color temperature is needed before an average person can notice that difference?    (answer)

Are there any specific details in 45:0c reflectance measurement, such as the effect of distance between detector and sample or distance between light source and sample? Are there restrictions on the circumstances, like the color of the floor on which we put our sample?    (answer)

Is there any approximation to convert between Hunter Lab (illuminant C, 10 degree observer) and CIELAB (illuminant D65, 10 degree observer)?    (answer)

I received data from two sources. The first measured Hunter Lab on light source C under 10 degrees, the second measured CIELAB on light source D65 under 10 degrees. I don't have the spectra. Is there any approximation with which I can convert between them?    (answer)

What observer for XYZ values can be used in CAM02, 2 degree or 10 degree? Some articles use 2-degree observer, the others use 10-degree observer.    (answer)

I am looking for the differences between red, blue, green, and yellow dye. Can you tell me anything different about them, other than they are different colors?    (answer)

What part of the spectrum helps grass grow?    (answer)

Why does the color of a crayon or colored pencil look a different color on paper? For example, some purples show up blue on paper.    (answer)

Would a spectrophotometer be able to accurately read the color differences between chrome plated surfaces? (ie. mirror-like finish) What settings or type of instrument would best achieve this?    (answer)

Is it possible to quantitatively describe a color just by its reflectance or radiative spectrum?    (answer)

How a mixture of R, G & B single wavelength sources (such as RGB laser) can produce white light even though they do not cover the whole spectrum?    (answer)

Is there a formula for calculating Delta E in Munsell?    (answer)

I would like to convert from CIELAB coordinates into the approximate spectral red green and blue component curves. Is this possible?    (answer)

Why do we see colors when we spin a disc that contains figures in black & white?    (answer)

When job requirements demand color discrimination, how often should employees be tested on their color perception?    (answer)

Is there a color model which would allow me to do the following? Given L*a*b*/XYZ/whatever coordinates of a color stimulus, given specified viewing conditions and color, what is the shape/size of the JND "ellipsoid" around the color, and what are the directions of the hue/chroma/lightness axes?    (answer)

Is there still a copyright on the Munsell color system? If so, who owns it?    (answer)

Which light colors are absorbed by a yellow tulip?    (answer)

A one dimensional halftone cell has 50% coverage with reflection density 2.0 and 50 % coverage with reflection density 1.0. How is L* calculated for this cell?    (answer)

Are you aware of any software packages or even just charts, that list Munsell colors by both code and name?    (answer)

What colors (in order) would best absorb a green 529nm laser light?    (answer)

Could you please tell me if there is any function that computes the chromatic adaptation and the color appearance for the various types of color deficiencies?    (answer)

How could I provide (or display) the approximate color of a star given it's Kelvin temperature?    (answer)

I am interested to convert a hex html or decimal rgb value to cie 1931. How can I do this?    (answer)

Is 0.05ppm a suitable tolerance for measuring absorption on a spectrometer for beverages? When is it no longer a visible difference to the naked eye 1ppm, 0.1ppm, 0.01ppm, etc?    (answer)

What is the best color to paint behind a High Defintion tv mounted on the wall?    (answer)

What dyes are mixed to get Dark Shell Gray?    (answer)

I am a retinal surgeon. We sometimes stain the retina with trypan blue in order to highlight superficial membranes that need to be peeled (over the retina). Is there a colored contact lens that I could wear that would highlight the blue spectrum more so that it would be easy to see faint staining on trypan blue on the retina?    (answer)

I would like to come up with a color scheme that assigns an absolute color value to common color words. In this scheme I would want scarlet to have a distinct and absolute value different than crimson or puce. Is there any site or program that has assigned absolute color values to the English names of colors?    (answer)

We measure several prints for our printer characterizations. Two questions: (1) what is best space to average - spectral reflectance, LAB or XYZ and (2) if we wanted to do a weighted average to reduce the weight of data which tended to be "inconsistent", how would we best do that?    (answer)

In the CIELAB color space, what is the approximate difference for each of L*, a*, b*, and ∇E that most people would not percieve as a different color.    (answer)

Are there guidelines or rules of thumb for how colors are perceived as "dominant" in an image? Are there differences in the perception of color dominance among different colors? If so, how is this described in the CIELAB color space?    (answer)

Where can I find a chart showing color names, the colors themselves and CIELAB color coordinates? Ideally, this would also show the RGB color coordinates. I have found many RGB charts like this but none with the CIELAB coordinates.    (answer)

Are there established color values for the color of skin for various ethnic groups (like Lab or Munsell for example)? This is for a makeup manufacturer who wants to design packing for specific groups of people.    (answer)

I dyed 100% cotton red, yellow and blue and placed them in direct sunlight for a week. The red appeared to fade the most, but I can't explain why. Can you help?    (answer)

Why does red disappear when viewed behind red glass?    (answer)

Are grey shades actually constant, because they are nearly achromatic, or is there something about eye biomechanics that create a visual perception not in agreement with spectral readings?    (answer)

I need to know the Munsell color for 'school bus yellow.' The unsourced quote I have says it is 9.4YR, 7.5/9.2.    (answer)

What does LCC stand for in the color science world?    (answer)

Where can I purchase a poster size print of the CIE 1931 Chromaticty Diagram? I realize that the diagram is only a 2D projection of 3D matching data however I still find it useful to illustrate some of the other attributes of the data depicted (color mixing, color temperature, color gamuts)?    (answer)

At what distance, target size and viewing conditions (illumination level/type) does the HVS's ability to resolve color breakdown? Put another way, what is the "chromatic" resolving power of the HVS and how is that defined in terms of distance, size, viewing conditions?    (answer)

Is black a natural color or is it just a very dark brown that people just see as black?    (answer)

We would like to know the complete Reflectance Measurement principle and formula for the dual beam color spectrophotometer including Light trap, PTFE standard and sample.    (answer)

Is there a relationship between visual lightness (when we judge lightness of color) and Light Reflectance Value (a measurement that is expressed mathematically?    (answer)

I am a massage therapist. After a massage a customer said that when I had massaged her on a certain part of her body she could see a certain color, for ex. red, & at another spot she saw the color blue. Is there a reason to this?    (answer)

How do you find a RAL equivalent of an NCS colour reference?    (answer)

Why can't humans see ultraviolet or infrared energy?    (answer)

What color is chroma key paint for green screen back drops?    (answer)

Is it possible to determine the ink densities (or transmissivities) in a small area (~20 mm^2) of a four color image (CMYK) from its reflectance spectrum? The relative areas of coverage and overprint of the inks are not known. Illuminant and substrate spectra are available.    (answer)

How would I measure the yellowness of the sclera (whites) of the eye? Also, what instrument would be an appropriate measure haziness of the cornea?    (answer)

What is the color temperature that makes the road most clear during driving, even under unconditional weather?    (answer)

How do I match the actual fabric color in PhotoshopTM? Images are digitally shot, and the final output is four color offset printing.    (answer)

What is the theoretical principals of the color change test in chemistry?    (answer)

I am interested to convert a hex html or decimal RGB value to CIE 1931. How can I do this?    (answer)

Is 0.05ppm a suitable tolerance for measuring absorption on a spectrometer for beverages? At what concentration is the difference not perceptible?    (answer)

What would an acceptable max display luminance setting be for a display that does not see direct sunight or much ambient light so that colors and text are easily readable?    (answer)

What is the unit of the viewing angle? Is it degree, radian or steradian?    (answer)

Using the color bar on Powerpoint 2003 I drag the brightness bar on the Device RBG mode, I get a darker color of apparently the exact hue. Is the hue is truly staying the same? Also, if I drag from R 200, to R150 to R50, is it decreasing in the amount of red equally in each interval?    (answer)

"The Desktop Color Handbook" mentions using a "light source color rendering card" which has patches that look the same under light of the appropriate CCT, but different under other lights. Do you know who makes such cards, or how one could create one?    (answer)

I am a Color Technician for a woman's retailer which specializes in black, white, and neutral only clothing. We test our associates with the Munsell 100 Hue test. Is there a similar test to evaluate for neutrals only?    (answer)

How can I convert RGB or CMYK shade to Pantone?    (answer)

Is there an accepted universal standard for the calibration of color Spectrophotometer? Are there white standards available with certified reflectance values?    (answer)

Are there maximum/minimum values for a* and b* like the min and max for L*?    (answer)

Is color a quality in physics?    (answer)

I have noticed a couple of different species of early-flowering trees have pink blossoms which turn white literally overnight. It is the speed of the process which is intriguing. Do you know how it works?    (answer)

Do you know where I can purchase Hess Ives Color standards, both physical standards and papers publications?    (answer)

How can tulips be so many different colors when they are the same plant?    (answer)

Is there such an instrument as a hand-held spectrometer for measuring the color temperature of light sources? If so, how much do they cost?    (answer)

Densitometers can be purchased with or without polarizing filters. Why are both types used? Which type provides the best correlation to perception?    (answer)

How do you convert ΔL ΔC ΔH values for colour differences in CIELCh to the equivalent ΔL Δa Δb colour difference values in CIELab, when you do not have access to the absolute values for the original measurements?    (answer)

Are there some basic averages for the LRV of human skin?    (answer)

At what age do children develop good color perception?    (answer)

Can you define what is Multiflux math model used in color mathing?    (answer)

I have used three online color space conversion calculators and I get three different sets of numbers when I convert from XYZ to RGB. What's happening? Who's right?    (answer)

Can light be a "Brown" color? If not, why not?    (answer)

What is the RAL number for PMS 268 plum? I've attempted to find a cross-reference tool and have not been successful!    (answer)

When purchasing an encapsulated Haz-mat suit, Level A, what colors have the best visibility for the different environments in which they might be used, i.e, sandstorms, snow, heavy rain, thick smoke, etc.?    (answer)

Roughly how large is the overall remaining perceptual non-uniformity of color tolerances in CIELab space, when using the ΔE94 and ΔE2000 color distance formulas? (as compared to the 6:1 non-uniformity of simple ΔE*ab)?    (answer)

How can I have someone create a paint for me using a theoretical spectral reflectance curve?    (answer)

How does chameleon paint (i.e. paint which color depends on viewing angle) work? What is its composition?    (answer)

How do I calculate the dominant wavelength of a color sample with X,Y,Z or x,y? I do not want to draw it in the colorspace.    (answer)

Why does your hair change color during the season?    (answer)

How to convert CIELAB data to Yellowness and Whiteness index?    (answer)

Which minimizes solar heat absorption better, polished aluminium or white paint on it?    (answer)

How does the eye determine the various colors of visible light?    (answer)

Could you please tell me, what color would 1.2Y 6/11 be?    (answer)

Why do black clothes appear blue in the artificial light of a clothing shop? Then when you take the item into natural light it is black? Why is that?    (answer)

What type of Pantone Guide shall we refer to & which instrument is suitable to measure the values of colour on aluminum foil with a flexo printing process? Since Aluminum has glossy as well as the matt finish then is there any need to change the settings of the instrument?    (answer)

We print on Aluminum foil with a flexo process. What type of Pantone Guide shall we refer to & which instrument is suitable to measure the values of colour? Since Aluminum has glossy as well as the matt finish then is there any need to change the settings of the instrument?    (answer)

How do I convert from spectral reflectance (from a hyperspectral imager) to CIELAB colorspace?    (answer)

Can a consumer grade flat bed scanner be used as a colorimeter?    (answer)

The lighting goal for our new indoor shooting range is to have 100 footcandles of light on each target. Our question is this: should the walls and ceiling around the target be light in color or dark in color?    (answer)

Can you suggest an ideal color scale for a digital elevation map to be printed in a scientific paper? Is it possible to have a color scale that looks good in color and in black and white?    (answer)

Suppose I introduce the same amount of noise in individual channels of a YUV image of 420 format (chroma has been downsampled). Which image is the most noticeable, the one with noisy Y, U, or V?    (answer)

Can you point me to the actual formula the Photoshop Hue/Sat tool is using to change given colors in an image?Can you point me to the actual formula the Photoshop (tm) Hue/Sat tool is using to change given colors in an image?    (answer)

What are the colors of a complete spectrum? (Starting with the color with the longest wavelength.)    (answer)

What color measurement system would be best to define colors for a liquid, to be described in a US patent?    (answer)

Why is blue ink most commonly used for writing?    (answer)

What is the difference between the L*a*b* values and the L a b values when using a Minolta colorimeter?    (answer)

Do you do research on ink jet printer color consistency? We are interested in printing solid colors for visual evaluations. We have a high-end ink jet and use photo paper, but we see color differences of up to 0.5 Units ΔE* between prints using the same printer, inks, profile and paper.    (answer)

My spectrodensitometer states its measuring geometry is 0/45, and its standard observers are 2 and 10. Are these angles related? Which should I use?    (answer)

Is there a way to determine what a symmetrical circle 1% dot, 120 line screen should measure? I am looking for a published table or a equation as I need to determine this on several different screen rulings.    (answer)

I am working on a plastic matched automotive black (GM 848) where the color is visually darker, but it measures LIGHTER than the standard. Can you please explain why?    (answer)

What is the mathematical equation to convert Lab or XYZ to Density?    (answer)

I sometimes catnap at my computer or while reading and when I wake everything looks green tinged for about 20 seconds. Why?    (answer)

Does the color of a laser affect the velocity of the light wave projected by the laser?    (answer)

What is the physics behind a blue-yellow polarizer such as the Singh-Ray Gold-N-Blue filter which photographers use to add yellow or blue highlights to polarized parts of a scene?    (answer)

Is is possible to convert R, G, B values of an image captured using a flatbed scanner to densities? I can convert R, G, B to CIELab using the ICC profile of the scanner. Is there a way to convert CIELab to Densities?    (answer)

Where could an art reproduction facility obtain an optical device that used spectral-based imaging?    (answer)

We know density is derived from the transmitted spectral power distribution. Can you suggest a reference that provides the responsivity functions for Status A and Status M densities, as well as the specific function for the calculation of density? Also, what is the proper illuminant to use?    (answer)

What is "camera gamma" and its relationship to NTSC/HDTV video?    (answer)

How does coloured text affect accommodation?    (answer)

How can I meaure the color of clear solutions? We want an objective measurement (wavelength) of colors of various juices and wines.    (answer)

When choosing an umbrella, what color is best to protect yourself from UV light?    (answer)

I am teaching color theory to our press operators and I am wondering if there is a full color spherical L*a*b model illustration that I can download, and if necessary purchase.    (answer)

I would like to know if the color of the water (by adding food color dyes) will affect the absorption rate of water and thus the color of the white flower over time.    (answer)

What is the Kubelka Munk Theory? What its use in textile dyeing process? Would you please provide me any literature on the Kubelka Munk theory?    (answer)

Is there an existing paint industry standard system for expressing (and thus potentially matching) all the visual characteristics of a metallic or metallic flake paint, whether one-coat or two-coat (colored transparent over metallic or flake)?    (answer)

I am trying to calculate the colour of a coating. I have a graph of wavelenth versus reflectivity. Is there a simple way to convert this graph into RGB values or some similar standard?    (answer)

Since a mirror reflects most of the light that falls on it, as does any white body, what is the difference between the two?    (answer)

I know that the color of a body depends upon the color that it reflects. What causes some bodies to be transparent, others translucent still others to be opaque?    (answer)

I found a source that says an RGB of 194, 32, 11 for Calder Red. Can you tell me what proportions of red, yellow, and blue paint should be mixed to get that RGB?    (answer)

Where can I buy Baker-Miller pink paint?    (answer)

I want to make a slate grey color from white exterior latex paint. What additional colors and quantities of color will I need to mix?    (answer)

This pertains to colors being used for home theater projection screens. Neutal grays have been suggested as the best color since they should not shift the color of the reflected image. Munsell grays are reported as neutral for illuminant C. What would the RGB value be for Munsell N8 and N9 under D65? One source lists N8 as 202 202 202 (L*ab- 81.3256 0.0044 -0.0087, Yxy as 59.0619 0.31272 0.32900). Is this correct?    (answer)

I am an artist interested in painting with photochromic inks or paints. Do you know of a supplier?    (answer)

We have two items painted with Munsell N7 which are significantly different in shade. Is this normal? How can I measure if the differences are within specification?    (answer)

I am building a pit solar greenhouse and need to decide what color to paint the non-glazed walls. White would be the best for reflection onto the plants but I am also looking for more pleasing colors. What is the best color for growing plants?    (answer)

Why isn't E point (x=0.3333 - y=0.3333) used as a standard illuminant for color matching and ΔE?    (answer)

I am working on honeybee color vision. Using a honeybee specific color diagram, we know how to calculate dominant wavelength. How do I calculate the dominant wavelength of a color sample which resides in my color diagram in the "magenta" (or purple) zone.    (answer)

Why are the colors of Christmas typically red and green?    (answer)

I work for an automotive finishing company and use an X-rite MA68II for measuring color. Which should I use, L*a*b*, or L*C*h°? Everyone seems to use L*a*b*, but I'm not sure why.    (answer)

How long does it take for your brain to recognize color?    (answer)

Can you provide a mathematical formula to convert a RGB color value in CMYK color value?    (answer)

How do mood rings work?    (answer)

At what illuminant temperature are Munsell neutrals (N6, N7, etc.) designed to be neutral?    (answer)

Obviously having a single colour on two different stimuli (each encompassing a different meaning) on a workstation will cause confusion. What are these problems from a psychological, cognitive, or ergonomic perspective?    (answer)

Are the colors that we see during the day, present at night - only we cannot see them? Or are the colors that we see during the day not present, or altered, because of the low light?    (answer)

What are the names of pigment suppliers who mfg or distribute metameric pigments?    (answer)

What are the evolutionary advantages and disadvantages of impaired color vision?    (answer)

I am developing paint color regulations to help buildings constructed on mountainsides blend into their surroundings to minimize their visual impact. What maximum LRV do you recommend for an environment typically consisting of darker browns, grays, and greens as the "base" colors in order to keep buildings from "standing out"? What would be the most appropriate instrument for measuring the LRVs of paint/stain for enforcement purposes?    (answer)

How does the color of a room affect people's moods?    (answer)

What are the equations for McAdams ellipses? Are they location dependent in the 1931 chromiticity diagram?    (answer)

It makes sense that I should want window glass with the highest Color Rendering Index available in the performance category that I need; but how do I judge the relative CRI when all options are between 87 and 95?    (answer)

What mixture of acrylic painiting do I need to achieve a copper tone?    (answer)

Can CAM02 to predict Appearance Correlates of a color on different colored backgrounds?    (answer)

Is it proper to state a Munsell notation for a metallic or pearlescent color, or is Munsell a solid color only notation system?    (answer)

Is it possible to draw plankian line in CIE diagram? How?    (answer)

Is there any source of spectral reflectance data for samples in the Munsell Book of Color?    (answer)

Does the Munsell system account for the Helmholtz-Kohlrausch effect?    (answer)

How closely do the Munsell Renotation data reflect the actual tristimulus values of samples in the Munsell Book of Color as viewed under Standard Illuminant C?    (answer)

Why does the sheen of a finish affect the appearance of a color? Do the wavelengths of color get magnified, refracted, or intensified as the pass through the layers of a paint film?    (answer)

Can you explain the difference between value and luminance? Is Light Reflectance Value different than luminance?    (answer)

I understand that the visible spectrum is comprised of the wavelengths red, orange, yellow, green, blue, indigo and violet. Combined they make up white light. So does that mean that white is then a wavelength too? Do all the other colors/wavelengths add up to something that we recognize as white?    (answer)

Does the color of your hair affect it's ability to keep your head warm?    (answer)

What's a good reference for information on the Munsell system?    (answer)

Where can I buy Color Standard for measurement calibration?    (answer)

To measure process color is it better to use a spectrometery or density, hue, and gray?    (answer)

Where can I find absorption or reflectance data for inorganic chemicals or pigments?    (answer)

Is there an index for the degree of yellowing? I want to characterize the degree of yellowing in trees as an indicator of poor health from aerial RGB photographs.    (answer)

Please give an example of how to begin with a tertiary color,subtract one color and then subtract another color but don't end up with a primary color.    (answer)

Where can I buy the Munsell color chart that has the 14 samples used for CRI tests?    (answer)

Where do the beautiful colors of fireworks came from?    (answer)

Why does the greenery of parks and gardens look beautiful to our eye? Please elaborate with regard to perception and function of the eye.    (answer)

Do you a reference for this equation used to get color decimal value from RGB values: "color_code = (r*65536) + (g*256) + b"    (answer)

How precise areMunsell color charts meant to be read?    (answer)

What makes colors fade in plastics? What part or parts of the light spectum?    (answer)

Are there any instruments or methods which measure the intensity of gray color?    (answer)

What the physical meaning of sharper cone reponse in CIECAM02?    (answer)

How do paint colors affect the room temperature?    (answer)

How can I mathematically find the best match for a CMYK color from an array of CMYK colors?As you have discovered, this is not an easy task. What you really want to do is convert your CMYK colors into a perceptual color space like CIELAB and then use color difference equations to find the nearest selections. This would require either some for of characterization or profile of your printing system.As you have discovered, this is not an easy task. What you really want to do is convert your CMYK colors into a perceptual color space like CIELAB and then use color difference equations to find the nearest selections. This would require either some for of characterization or profile of your printing system.    (answer)

I have some images taken with a digital SLR at the wrong white-balance setting (tungsten instead of daylight). Is there a fixed set of RGB correction factors that I can apply to the entire batch?    (answer)

Why do boys choose blues, grays, black, and browns when coloring and girls choose more brighter colors like greens, reds, oranges when coloring?    (answer)

Do some people, through genetics, have dramatically different "rods and cones" in their eyes and see colors totally differently than "most people". This does not include colorblindness, but that some people might see red as yellow and blue as orange, etc. Is this true?    (answer)

I am trying to establish a color system criteria for silicon parts which are white. What do you suggest in setting up a criteria for the color white?    (answer)

What is meant by plankian locus? What is its importance?    (answer)

Are there any estimates of the probability that a photon impinging upon a cone photoreceptor will be absorbed by the visual pigment within the receptor? How does this probability change as the radiance is increased so that more of the pigment is in the bleached state?    (answer)

Can a person with a color deficiency learn colors and shades and be able to distinguish differences even if they are not able to see the exact color that a normal vision person might see?    (answer)

Would it be possible to correct color blindness (for computer users) by measuring a user's color sensitivity at various wavelengths, then adjusting the output of the monitor to compensate for it?    (answer)

How do I calculate whiteness index (WI by ASTM standards) if I don't have a spectrophotometer but am in possession of reflectance data for materials that have <95% reflectance @ 600nm?    (answer)

I am a massage therapist trying to do research on what color is best to have in a massage room and how it affects the client, such as improves relaxation, promotes healing. Any guidance?    (answer)

Does a sheet of colored glass reflect, refract or absorb light? Or all 3?    (answer)

Could you possibly tell me the formulas for the harmonic equivalents (tones) of red, orange, yellow, green, blue, violet?    (answer)

I need a fairly fool-proof way for a moderately skilled technician to measure a large number of samples and present the data using the CIECAM02 coordinates. I am willing to buy a new instrument/software. Any thoughts?    (answer)

Is pink a shade of red?    (answer)

I am studying the colour of abalone shells. How can I statistically differentiate cbetween two shells? Eg: this shell is bluer than that one. I plan to use digital photos, D65K light with the camera at the normal angle.    (answer)

Does the color of one's eyes (light colored vs dark color) have any effect on vision?    (answer)

Can the color of the bedroom walls prevent proper sleep? My husband sleeps fine in a blue room, but has trouble in a red room (same bed!).    (answer)

Are car color choices determined by age, gender or ethnic group?    (answer)

What is linear tiff data. What does it record?    (answer)

What are the differences in perception of color by males and females?    (answer)

Does the color of glass effect the index of refraction?    (answer)

Why do colors abosorb and/or reflect heat?    (answer)

What trends are typical when Munsell testing a group of people? Are there effects due to age, gender, education, or ethnicity?    (answer)

Why doesn't Pointer's gamut (CR&A, 1980) fully cover all real points in Munsell system as defined by real.dat?    (answer)

I heard that HDMI for HDTV's can have billions of colors but I also heard that our eyes can only see around 10 million colors. Does this mean all that extra color doesnt matter or will it seem clearer in some way?    (answer)

What color do most people answer when asked to name a color quickly?    (answer)

How can I get spectral reflectance information about Color-Aid samples?    (answer)

Is there any standard by which Munsell colors are called "light" or "dark" or are those terms that are too subjective so that they don't get used?    (answer)

Do you know of any freely available color matching software?    (answer)

sRGB has a gamma of 2.2. Why do the equations have an exponent of 2.4?    (answer)

Can you comment on how does the following colors affect human psychology when considered in relation to fashion designing: red, yellow, blue, green, orange, violet, brown, pink, white, black, grey?    (answer)

Are there any filters that can be placed over the eyes to make a substance, which is invisible to the naked eye, visible through the filter? Can you give an example?    (answer)

Can you provide me with a formula for RGB values given Munsell coordinates?    (answer)

Is there a range of Munsell or L*C*h coordinates that would describe browns?    (answer)

With all things being equal, is there any reason to see an increase in black dot gain simply by changing the print sequence from CMYK to KCMY?    (answer)

What is the ideal working space for digital painting in Photoshop and painter is. I tried using Adobe RGB but my reference images look so saturated.    (answer)

What color is best to paint a room with hardwood floors to enhance productiivity?    (answer)

Is there a guideline, perhaps application-based, for the number of patches needed to make adequate ICC profiles for printer output? Is there an upper limit on the number of patches beyond which more patches do not necessarily improve the ICC profile?    (answer)

I am looking for products to protect my eyes from UV-C light (254 nm). What substances are opaque or reflect to UV-C light? How harmful is UV-C light to human skin and eyes? Can you suggest any protective measures I should take?    (answer)

hat is the correlation between Hunter whiteness (L, a , b) and CIE whiteness (L*, a*, b*)? Can I relate them mathematically?    (answer)

I have a Minolta 2600d portable spectrophotometer. Can you tell me the best way to measure the fluorescence of teeth in vivo? Also, can I use the 2600d to measure the opalescence of both natural teeth and dental materials?    (answer)

Is there a certain color that has been proven to be least tiring to the eye on web page backgrounds?    (answer)

What are the calculations used to convert spectrophotometric spectral data to density, CIE XYZ, and RGB variables/values?    (answer)

Why can't humans see colors that fall in the UV or IR part of the electromagnetic spectrum?    (answer)

Could you please tell me the equivalent Federal No. (Std 595) for Munsell No. 2.1 YR 5.6/16 (Orange)?    (answer)

How can I convert NCS color mode to RGB mode in Photoshop?    (answer)

Can you explain how detergents would cause color fading?    (answer)

Do HSV and HSI refer to the same model? If not, what is the difference?    (answer)

How often should color vision testing be assessed if the ability to see colors is important in one's occupation?    (answer)

I would like to make a children's computer program emulating colour mixing of paints. Since coputers generally use the RGB colour model, I don’t know how to achieve this. Can you help?    (answer)

Can chromatic discrimination change over time or can it improve through practice?    (answer)

Any correlation between age and chromatic discrimination ability?    (answer)

Do any illnesses/physical characteristics/disabilities impact one's chromatic discrimination ability?    (answer)

How can a color display with three monochromatic lasers produce a finely rendered colorspace, with what seem like the appropriate pastels and everything?    (answer)

What are the different textures of colour?    (answer)

How can I convert CIELCH to CIE 1931 x,y coordinates?    (answer)

What is the utility of converting tristimulus values to L*a*b* values?    (answer)

Can my company's color references be accurately reproduced 10 years from now based on the tristimulus values we maintain ?    (answer)

How do the eye and the brain work together to create the chromatic adaptation 'illusion' effect with colours? Also, why does looking at certain stimulus for certain lengths of time effect the time span of the adaptation?    (answer)

What makes wet grass greener than dry grass? A scientific explanation of more than just refractive index would be much appreciated.    (answer)

What does the ratio b/a give or mean? Here a is negative and b positive.    (answer)

Can you provide list of non toxic pigments that are insoluble in water measuring about 1 micron particle diameter?    (answer)

I am preparing a 3 band fluorecent lamp powder recipe for color point x=0.312, y=0.336, Ra= 82,SDCM<3. Can you provide any useful recipe development procedures, methods or any useful website for me about the color coordinates adjustment?    (answer)

Can you help me transfer color temperature to 1931 CIE xy-coordinates?    (answer)

I am shopping for a new motorcycle helmet and want to know the color's that would keep my head cooler in the sun. Where do colors such as grey or silver fit in as far as reflecting light/heat and staying cooler?    (answer)

Is there any research on changing the colors of a light to improve a surgeons abilility to see in different surgical enviroments? Can you improve their contrast sensitivity like skiers do with colored lenses.    (answer)

How do I assign a RAL number to a standard color used by my company?    (answer)

I'm measuring several 3000K white lamps. I'd like to know the color variation of these lamps. Is there any other way to measure color variation of a population of lamps, aside from standard deviation and MacAdam ellipse?    (answer)

I require formulation for a Paint that absorbs magnetic rays or RF energy used by RADAR and do not reflect back.    (answer)

Is it possible for a liquid subtance to appear clear or colorless when placed on a white piece of paper with the naked eye, but will appear a unique color when seen through a filter?    (answer)

I am interested in obtaining a very accurate spectral match of my color sample. Some of the color matching systems I have used in various paint stores do a pretty good job of matching the color but not necessarily the spectrum of my sample.    (answer)

Can you explain which coloured dyes change colour or fade and why when used as a gamma radiation dose indicator?    (answer)

What is multispectral image?    (answer)

What is the problem if a person sees both gold and silver as silver? This person also has red-green defects.    (answer)

What is the top that is black and white and makes pale colors when spun?    (answer)

I would like to perform the Farnsworth-Munsell 100 hue test on my monitor. Will this work? Can I have the values of each colour caps to form the colours?    (answer)

I am creating a colorant database for my matching software. How do I reduce the bronzing of Pth Blue at high concentrations?    (answer)

Which colored paper reflects more light?    (answer)

The color of an object depends on the reflection and the absorbtion of light. How?    (answer)

What are good books to get detailed information on both the Munsell and CIE systems? I'm an artist and have a general education of both systems but would like to know indepth knowledge of each, including the math and reasoning behind the constructions of each system.    (answer)

I am building a fiber glass airplane. The kit mfg says paint it any color you want as long as its white due to heat build up in the sun. Any idea of how far off-white I can get? How can I calculate the increase in heat absorbtion if I go a little blue or yellow off of white?    (answer)

Is there a specific color that could be called Munsell green? What is its Munsell designation? I understand this color is commonly used at places like university campuses for exterior electrical equipment enclosures.    (answer)

How is the location of an illuminant on the Planckian Locus and R-G Axes related to colour vision tests?    (answer)

What is the "straight line rule" when referring to the CIE 1931 Chromaticity Diagram?    (answer)

Which RGB values or others make color that is visible only under ultraviolet ray on the white paper?    (answer)

If one measures same color on various spectrophotometers the spectral profile is the same,but there are differences of 2-3 % in reflectance. Can you explain why? Which is the most correct reading?    (answer)

Can I use BCRA standard tile for calibration of spectrometer? Where can I buy it?    (answer)

What are the advantages and disadvanatges of chromaticity diagrams?    (answer)

Can you please define "dominant wavelength" and "wavelength of maximum absorbance"? Which should be used in the calculation of strength?    (answer)

I am writing a story about colour for children. Can you help explain (in simple terms) how a rainbow works and how the mixing of just a few colours in printing pictures in papers works?    (answer)

Would you recommend a source for standards tile for calibration of spectometer?    (answer)

How long does it take to perceive color? Are some colors perceived more quickly than others?    (answer)

I have an RGB digital SLR camera. Is it possible to find relationship between the camera output and the spectral reflectance of objects?    (answer)

How can I determine color names corresponding to hex color values?    (answer)

What is the meaning of NET profiler of a color spectrophotometer?    (answer)

When I measure delta L on low-gloss (matte finish) parts, I notice more variation between measurments than with higher gloss parts. Is there a scientific reason for this? Does the gloss play a roll?    (answer)

How can I extract a specified color from an RGB image using Matlab?    (answer)

How does one go about using use color measurements to determine the concentrations of colorants/dyes in aqueous solutions?    (answer)

I evaluate llighting systems by measuring u'v' with a spectroradiometer. How can I calculate deltaE color difference from this data?    (answer)

How is the Light Reflectivity Value (LRV) measured? Why do building codes require a certain percentage of LRV in the materials used?    (answer)

Do people with light colored eyes have better night vision than people with dark colored eyes?    (answer)

Do you know of a color/temperature chart showing various colors and their related heat reflection/absorption properties?    (answer)

What sorts of jobs would a color scientist do?    (answer)

What is the relationship between the CIELAB a*-b* opponent axes and the perceptual unique hues?    (answer)

When the 3 hands on a spinning toy (which are 3 different sizes, long, medium and short) spin around really fast, they leave 3 "trails" of light in concentric circles. Why do we see 3 complete circles of light all the time?    (answer)

Why do colors fade in the sun? is it the heat or the light?    (answer)

Do humans have a natural affinity for certain sorts of colors more than others as compared to other creatures?    (answer)

Do insects that have UV sensitivity in their visual system see the UV portion of the spectrum as "color"?    (answer)

Is color limited to the interaction of light with an object and our eyes?    (answer)

If no light is falling on an object, does it still technically have a "color"?    (answer)

How does a color TVthere is a great website describing how TV works at . work?    (answer)

How can I know the spectral sensitivity of a common CCD camera?    (answer)

Does the color green inspire thought?    (answer)

Do objects that are the same color have the same chemicals (elements) present? For example if I looked at the chemicals in red paint would I find the same ones in a red flower?    (answer)

How I can mathematically convert from CIELAB (D65,10°) to XYZ (D65,2°) or RGB?    (answer)

How do the colors you wear affect your appearance? What colors make you look certain ways?    (answer)

What is an easy way to create a color scheme using an elliptical path and a Munsell conversion program?    (answer)

Is the temperature the same in shadow under a dark colored fabric awning as under a a light colored awning?    (answer)

Sailors know from experience that darker colored fabrics last longer in full-sun exposure than white or very light colored fabrics. I am specifically referring to Sunbrella bimini and sail cover fabrics. Why?    (answer)

How do grey scale images differ from color (RGB) images?    (answer)

How can I match a paint color to Munsell N8?    (answer)

I'm looking for a Circular Spherical Vision Spectro Colorimeter for analyzing luminance and other parameters (axis etc...) of reflective materials in different colors for road construction. Can you help?    (answer)

Is there a source for a neutral gray paint designed to be used on floors and/or walls in a TV broadcast studio?    (answer)

I would like to find pigments with relatively narrow spectral aborption bands. The goal is to create paint which offsets the peak emission lines of different artifical light sources. Can you help?    (answer)

As an Interior Design student I know that paint manufacturers, geologists, anthropologists, and color designers use the Munsell system of color notation. What other industries currently his system to code their color? Automobile industry? Textile Industry?    (answer)

Why do we recognize uniqueness only for four colors, blue, yellow, green, and red? Is there any color map of unique hues in a visual system?    (answer)

How do we see metallic colors like gold and silver?    (answer)

Why is a red Popsicle red?    (answer)

What is the difference between value and chroma? If I add black or white to a color I am changing its value. How do I change its chroma?    (answer)

I measure pigments from bird egg shells with a spectrophotometer CM-2600d, should I work with 100%UV or 0%UV? What about pigments from bills and legs of birds?    (answer)

Out of blue, green or peach, which color is more likely to attract flies or insects and why?    (answer)

What effect does light have on white paper: does it reflect or transmit?    (answer)

What is chromatic textile? What properties do this textile have?    (answer)

How do I compute the correlated color temperature of an Lab/Luv color coordinate?    (answer)

I'm trying to understand whether there is an optical/physical basis for this "chameleon effect" (the ability of the materials to blend with surrounding tooth structures to create naturally appearing restorations) and whether there may be way to measure it.    (answer)

I'm looking for the paint formulation for the official colors of West Virginia University. The Pantone colors are either: A) PMS 873 metallic gold and PMS 295 Navy Blue or B) PMS 124 Gold and PMS 286 Blue. Can you help?    (answer)

In your opinion what pantone color best defines TEAL?    (answer)

Can you help me calculate the color difference between my Macbeth Colorchecker and its image after capture and display on an LCD monitor?    (answer)

I would like to purchase a grey scale color variation kit for comparing the change in color wash for Denims and Textiles. Can you recommend a source for this kit?    (answer)

Why does eye (iris) color appear to fade with old age? Is it because of the yellowing of the lens?    (answer)

Where can I find a tabulation of all pairs of distict spectral monochromatic lights that are perceived as achromatic?    (answer)

At our paint-supply company we need to match a color to existing color on a clients' wall. Is there a portable instrument we can use to determine the required mix to match the exisitng paint?    (answer)

How can I know the tricolor chromaticity coordinate of a common CCD camera?    (answer)

How does color affect our vision?    (answer)

How do I calculate the chromaticity coordinates of a single wavelength of light?    (answer)

What factors affect the intensity of color?    (answer)

What do I tell the paint store to mix in order to get a color that best matches a wavelength (5040 Angstroms)?    (answer)

Do different people see the same color in different shades? Why?    (answer)

How does one resolve the concepts of the 'scientific' (linear) color frequency model and the 'artistic' (circular) color wheel model in regards to color perception?    (answer)

I have a thin PET film that is colored with dyes. I am suprised by the amount of dye required to match the opacity of the current film. Would you say that dyes are more linear than conventional pigments are when referring to thickness and saturation?    (answer)

Do you have a table of NCS color code corresponding to RAL color code?    (answer)

What does RAL stand for?    (answer)

I am a member of an internet forum dedicated to the Rubik's cube. What is the set of 6 colors (including black/white) that human eye is best able to discriminate?    (answer)

What is the equation for plot a MacAdam ellipse? Also, what steps are the Macadam ellipses on the standard x,y chart and what do these "steps" mean?    (answer)

I am a competitive rifle shooter. Are there any colored filters to place in my rifle sight that would help to reduce eye fatigue or even simply aid in aligning things?    (answer)

What is the best method to measure the opaque black color of a plasic material?    (answer)

What distance can humans still distinguish between different colors?    (answer)

What wavelength out of red, green, blue and full spectrum would purple cabbage reflect, and what would it absorb?    (answer)

Is black paint recommend for a boy's bedroom?    (answer)

What's the RGB composition of RAL 7005 & RAL 1021?    (answer)

How can I measure the LRV value of something. Or can I convert CIELAB data into an LRV value?    (answer)

What material has the most uniform reflectance spectra, including visible, IR, and UV?    (answer)

Why are common soccer balls black and white?    (answer)

Can you help me convert between Pantone and RAL colors?    (answer)

Do clear objects reflect or absorb heat?    (answer)

Is there a simple formula to take numbers obtained by matching paint samples to the 1929 Munsell book and convert them to the numbers that would be obtained using the current Munsell book?    (answer)

Is it possible to make a color that is not visible to the human eye?    (answer)

Do age and gender matter when seeing color?    (answer)

I need a color swatch for 10YR 9/1, do you have this?    (answer)

We are trying to measure color reproduction for digital cameras using the Macbeth ColorChecker. We image the Color Checker under various illuminants. Is there a better metric to calculate the color reproduction than ΔE?    (answer)

I am trying to image a white fabric bag using a light source inside of the bag. Are there any wavelengths of light that would be most appropriate? That is, which wavelengths might be absorbed by a white acrylic fabric?    (answer)

What colour paint dries the fastest?    (answer)

What hue can the human eye dicern the most shades of?    (answer)

What does the color blue mean?    (answer)

When reading a violet, what does the Δa and Δb values represent? Example is the Δa dirty/clean or red/blue?    (answer)

In literature about discoloration of wood (furniture or parquet floors), UV-light is mentioned as the cause for the discoloration. But doesn't the glass window act as a UV-filter? So is the discoloration caused by visible light instead of UV-light?    (answer)

How I can find the formulation of paint after coating?    (answer)

I am wanting to know how broad the primaries were for the 1931 color matching experiment. Were they monochromatic, as in a laser? If not, what was the spectral half width at half max for each of the colors?    (answer)

Does the color of an ice cube affect the rate at which the ice cube will melt ?    (answer)

Can you tell me please what the CIELAB reading is of matte Munsell gray to be used inside color viewing cabinets for the print industry?    (answer)

I would like to measure the color intensity of various parts of birds. What instruments will I use?    (answer)

Why does some plastic yellow over time?    (answer)

Can you help me convert between candella and power wattage as measured by photodiode?    (answer)

I am trying to characterize my computer display. I have a failure of additivity. That is, the sum of the individual R, G, and B XYZ values does not equal the XYZ of white. Can you help?    (answer)

Can the brain take a 2D image (eg: a picture) and convert it to a 3D image?    (answer)

Assuming a monitor calibrated to the sRGB standard, is there a combination of available adjustments (gamma/contrast and/or saturation) that can be calculated and used to provide a better 'ballpark' display of an NTSC signal on an sRGB monitor?    (answer)

Can you tell me what color eye shadow would look the best for a given complexion?    (answer)

Can you tell me what the cmyk formula for silver is?    (answer)

Do different colors affect your eye sight different over time?    (answer)

Can one measure color through heat frequencies?    (answer)

What are the colour combinations or chemical substances that can be used to obtain jet black colour in a cotton flannel material?    (answer)

What is the real meaning of color blind?    (answer)

Did humans use chromatic adaptation long ago, for example in hunting?    (answer)

Does the color of your eyes affect your vision? Do people with blue eyes have better vision than those with green?    (answer)

What is the minimum ΔE that a human eye can detect? Which &Delta E"    (answer)

Do you know of any table of rgb value pairs that make up visual complementaries (colors that are afterimage of each other)?    (answer)

What color of construction paper fades the fastest?    (answer)

Why is blue light plus yellow light equal white light, but blue and yellow paints mix to green? Why do the color wheels from various systems use different primaries?    (answer)

When refering to "pure" colors (red, green, blue, orange) what is the corresponding notation in the Munsell system?    (answer)

What's method that appropriate for measure color of gemstone?    (answer)

How does color affect our mood?    (answer)

Which of these Munsell soil designations is the reddest: 5R 6/4, 5R 5/2, 5R 7/3, 5R 6/3?    (answer)

Can you help me explain (in simple terms for a 5 year old child) why some colors of popsicles melt faster than others?    (answer)

Can you provide the pantone equivalent to GE plastic FXM171R-GY2A360M?    (answer)

Can you help me find a cost-effective way to measure black-gray-white and all shades in between. My son is doing an science experiment to determine how well erasers work.    (answer)

Can you help me create the color green that is exactly in the middle of the green color spectrum using the RGB values of my display?    (answer)

I need an example or a graph help to explain why humans cannot see colors that fall in the ultraviolet or infrared part of the electromagnetic spectrum.    (answer)

Specifications on the web given by SAE, ECE eg, mention that the colour should fall within the given boundary:
y = 0.335 (yellow boundary)
y = 0.980 - x (purple boundary)
What does this mean?    (answer)

Is there anyone who I can pay to convert 12 colors with LCh values into Lab or Munsell values?    (answer)

In my prepress company we have to convert fabric samples by eye in to CMYK values. This is time consuming. Is there a software hardware combo that can read a piece of fabric and give the best cmyk values in a specific profile?    (answer)

How does the eye see colors that are moving very rapidly? (eg: a spinning color wheel)    (answer)

Why does light create color?    (answer)

What is neutral grey colour shade and the pantone number for neutral grey in pantone formula guide solid uncoated and uncoated ?    (answer)

How can I make a colored chromaticity diagram?    (answer)

Could you recommend a good website for the glossary of color imaging terms?    (answer)

Do you know of any research into the quantity of a particular colour eg., yellow that is in a painting and whether that painting is one that gives pleasure?    (answer)

Which colour has the most easily visually discriminable levels of saturation? The literature seems to suggest blue violet as this has the most steps when white light is added in 'just noticeable' amounts - would you agree with this?    (answer)

What do the various CIE illuminant designation mean (D55, D65, etc)? How are they related to each other and to CCT?    (answer)

What colors should I use for my experiment on which colors absorb more heat? I already know I am doing black and white.    (answer)

How do colored objects reflect heat?    (answer)

Can you help me transform Lch values to Lab?    (answer)

Does the first color you see when you wake up effect your mood?    (answer)

Does the color of your car determine the temperature in the car?    (answer)

Do you think people can remember words better from colored paper or white paper?    (answer)

I would like to do a science experiment on "Will male and females chose the color that has been associated with their gender?" For example, pink for girls and blue for boys. Can you help be to create a 5th grade science experiment to test this idea?    (answer)

In literature it is mentioned that the difference between SCE and SCI color measurements gives an indication for the gloss of the surface. Which parameters are used to evaluate this: the difference between the SCI and SCE values for CIE-L, a, b or a combination?    (answer)

What would be the reason to use CIELAB, CIELCH, CMC, CIE94, and CIE2000 (all of the above together) to calculate color difference from sample to standard?    (answer)

What is the best way to test color fading in construction paper? My child is making an experiment on what color will fade the fastest when exposed to sunlight.    (answer)

What chemicals are used to create fluorescent paint?    (answer)

Can you provide the CMYK formula for ANSI Safety Green?    (answer)

Is there direct co-relation between CIE 76 and ANLAB 40 and ANLAB 50 color spaces?    (answer)

What is the primary calibration of a spectrophotometer?    (answer)

Please explain the Bradford Chrmatic adaptation transform as a physical phenomenon and provide the mathematical basis.    (answer)

Are HSL values that the Paint accessory of Windows system use recognised by CIE ?    (answer)

Is there a mathematical conversion from RGB to HTML color code?    (answer)

Can you derive CIELAB values directly by visually inspecting the reflectance curve?    (answer)

Can you explain the mechanism of UV filter in color spectrophotometer, to get universal Whiteness values on all spectros. Is it a wedge filter or an attenuator filter.    (answer)

Does the color of light affect how much snow is melted?    (answer)

Can human eyes see noise? Or, can our brain recognize what's signal and what's noise?    (answer)

I work in printing. Can you tell me what the effect of dot gain is on delta E? Also, can we get an accurate delta E measurement from a coated sheet to an uncoated sheet?    (answer)

What colors absorb more heat, when a piece of ice is sitting on the piece of paper on a hot and sunny day?    (answer)

How specifically does a magenta-dyed silver halide crystal absorb green energy? I know it has to do with wavelength ... is magenta somehow 'dovetailing' with green light to chemically interact?    (answer)

How do I figure out what color a reflection of another color might be? For example, if I have a yellow car and something red is reflecting off of it, what color will show up as the reflection on the car?    (answer)

What effect renders UV lamp when selecting the colour with use light booth?    (answer)

Which will melt faster, blue Popsicles or red Popsicles?    (answer)

What would be the ideal color for drafting rooms or any rooms used by art students?    (answer)

What is a full-spectrum paint and what is it good for?    (answer)

Is there a concordance listing the ISCC-NBS color name for each chip in the Munsell Book of Color?    (answer)

When visually comparing colors, why is D65 light source better to use than Illuminant C?    (answer)

We are looking at colour and redness of scars on human skin. Which is better for the job, a hand held spectrophotometer or a hand held chromameter? Some literature validates the use of a chromameter CR300 in skin research, but spectrophotometers are apparently more accurate.    (answer)

Can you tell me the name of any software for changing a gray image into color. Is any software to convert a real time gray video to color?    (answer)

I can get x,y,z color coordinates. So how would one relate to the materials response for a particular wavelength?    (answer)

How can I calculate hue angle from CIELAB? What is pi?    (answer)

Is there something like color adaptation? I was wearing a blue light filter over one eye and felt that the differnce in color perception between the right and left eye disappeared after some time. When removing the filter, color perception in the previously uncovered eye felt like wearing a blue light filter for a short period of time.    (answer)

What is the RAL number that should be used in the background of a light cabinet?    (answer)

If someone walked down the street, what color clothing or facial features would that person have for me to easiest remember him/her?    (answer)

Does age and sex determine what color car a person buys?    (answer)

We are a printing company. We print offset (litho), gravure and flexo, both on coated and uncoated paper. What spectrophotometer should we buy spectrometer for Quality Control and Color matching?    (answer)

I am doing a science project on what colors are easiest to see in the dark. Can you help me figure out what experiment I should do?    (answer)

I want to purchase an LCD HD TV. But I can't decide between 2 TVs. One boasts 3.2 billion colors and the other 16.7 million colors. Do I care?    (answer)

Does the color of water effect its heating rate?    (answer)

I capture video camera RGB values through a microscope for image analysis of translucent microfossils. If I repeat this using a different camera I get different RGB readings. Are there any translucent standards available that I can use to calibrate between the two setups?    (answer)

I would like to ask if colour filters use to photograph - the filters we use to put in front of a lens in a camera- is a subtractive method?    (answer)

Where can I purchase a "student model" Munsell Color Tree?    (answer)

I need to measure human skin color directly. What instrument should I use?    (answer)

I am building a color & B/W headshot photo lab. My primary light source is 5000K fluoresent tubes with a CRI rating of approx 93. Since skin tones are critical, what color should I paint the walls?    (answer)

How do yo measure ΔE*cmc, ΔE*94, ΔE*fmc2 from the L*, a*, b*, C*, h* ΔH*, ΔE*?    (answer)

How can people distinguish edges of objects? Is this a function of rods or cones, or some organs else?    (answer)

I have a mapping website. Is there any function or algorithm that produces a collection of discrete colors that all have some minimum level of perceptual contrast between each other?    (answer)

When measuring the color of colored plastic plaques with a spectrophotometer, how thick should the plaques be and why?    (answer)

On what things color depend so that only some colors disappear while others remain?    (answer)

Are there metrics that quantify whether items in an image are discriminable or identifiable?    (answer)

Where can I buy Baker-Miller Pink?    (answer)

I am doing a problem on image permanence for large format inkjet. Should I use Delta E or Delta E 2000? Why and what is the difference between the two?    (answer)

Could you help me convert the Munsell codes to RAL codes?    (answer)

Will we ever be able to see colours we have never have seen? When I tell other people about my wonder to have different perceptions they think it is bogus. Will genetics and medicine make it possible in the future? When?    (answer)

Why is it more difficult to say the color of the word when it is printed in a different color?    (answer)

We always measure the color difference by using d/8 spectrophotometer with included specular reflectance. But why do we always measure the white with excluded one ?    (answer)

I have an emission spectrum from a sheet of luminescent material. Can you help convert the emission spectrum to an RGB color to display?    (answer)

Can white light be captured inside an opaque container. If not, why? When the source is disrupted it becomes dark. why?    (answer)

What is the best color model for use with colors that have a low saturation? CIELAB is not working for me because when a* and/or b* are close to zero I get poor values for hue.    (answer)

Can you hep me match the PPG paint color "burnt copper" with a CMYK color so I can print material that match the paint on my motorcycle?    (answer)

I have to purchase a system to compare shades of yellow in plastics with rough surfaces. Would you please recommend a company and/or instrument that would have good repeatability and be low maintenance    (answer)

Are RAL 7032 and ANSI 61 are same colours? Where I can I locate a colour cross reference table between RAL & ANSI standards?    (answer)

Why are there chromaticity values of zero or less than zero in the Munsell data on the MCSL web site?    (answer)

How do I measure contrast?    (answer)

Do the tiles in the Farnsworth Munsell 100 Hue test kit require calibration? If so, what can change that would require their recalibration? If they require calibration, what is the frequency?    (answer)

Does there exist a (known) correlation between a Minolta CM3500D and a BYK Gardner or does this depend on the product type?    (answer)

What are "suprathresholds" and "thresholds," with reference to color difference?    (answer)

Can the Munsell 7GY3.29/1.5 Green be converted into a ANSI number?    (answer)

What color will a solution that absorbs all the green, yellow and red light appear?    (answer)

CIE chromaticity diagrams are usually exhibited in a shape of a hoof. Why are the single waves spread on the ellipse side instead of the straight?    (answer)

Do you know the RAL Number for a cream colored paint known as Queen Ann or Magnolia?    (answer)

Of papers colored blue, white, red, green, purple, yellow, and black, which would be easiest to remember things if they all had black letters (except the black paper, which would have white letters)?    (answer)

Why do flat black objects get hotter than lighter colors?    (answer)

Which color model is best suited for tonal changes (i.e. curves) without changing the perceived color (hue, saturation; however defined)?    (answer)

Suppose that we want to measure the difference between the color of a test object and a reference object. How would I choose between using RGB color space and CIE Lab for color difference?    (answer)

Can I determine the color rendering index of this source purely from the light-emission spectrum?    (answer)

We capture colour images printed on paper through a CCD camera. How can we eliminate the scattering effect of the paper and to account for optical dot gain?    (answer)

Is there a chemical compound for invisible uv red ink compound. How we can get some or make our self?    (answer)

I want to create 3D look up table for CMYK data using Matlab. Can you help?    (answer)

Are there any objects that can physically reflect UV light to be able to be seen with the unaided eye?    (answer)

Can you provide an example showing how to calculate ΔE using Δa*, Δb*, ΔL*, ΔC*, Δh for textile pigment?    (answer)

I want to see what make-up shades and colours suit which skin tone, for a school project. Please get back to me with a colour wheel and and some useful information.    (answer)

I'm a wood scientist. Can you help me convert values from NCS to CIELAB?    (answer)

Should ideally conditioned standards (kept humidity controlled, dark envelope, minimum exposure to light, minimum handeling) develop metamerism?    (answer)

I have a Munsell paint specification of 7GY3.29/1.5. My paints use IF numbers. Can you help me transform this request to an IF number?    (answer)

Does the melting rate of a substance vary by color?    (answer)

Why does the spinning Benham top look colored? Is there any simple explanation of that phenomenon?    (answer)

How is a star's color different based on the temperature?    (answer)

What size print can I make with a 8 megapixel camera? If I print in high resolution (300dpi) and low resolution (72dpi). There is any formula to do that transformation from megapixel to inch?    (answer)

Can you help me compare RAL specification paint with ANSI paint for color match?    (answer)

Please can you explain what Macadam limits are (as mentioned in description of the 'real' set of Munsell values on your Munsell Renotation Data page)?    (answer)

I am searching for paint color mixing recipes for liquid (bottle/jar) opaque water based pigment paints. I have found a book of colored paint mixing recipes for paste (tube) bodied paints with a volumetric proportioning system for only paste consistency (tube) paints: Color Mixing Recipes ; by Walter Foster Publishing Staff, (48 pages, Trade Paperback); 2005. Do you have any resources and/or pertinent leads that you could provide me?    (answer)

I am a dental student. As part of my project I need to convert the RBG values obtained from Adobe Photoshop into CIELAB values in order to compare with values obtained with a spectrophotometer?    (answer)

Can you explain how to select the color center (or sample color) which can be used to evaluate color difference formula?    (answer)

I am trying to find a precise, systematic way to describe the colors of inks and metals used in medieval manuscripts. For example, I want to be able to define "red" as a range of similar colors and "scarlet" as a different range.    (answer)

Can you help me to discriminate between color space, color model, and color system? I'm confused!    (answer)

People of my area prefer reddish black on textiles. What kind of black do people in your area prefer on textiles?    (answer)

As we know black colours, for example on textiles, usually have a pale tint. Is there any formula for measuring blackness?    (answer)

How can light affect an interior color? For example: what is the effect of natural light on a red wall, blue wall, etc.    (answer)

Where can one buy an anomaloscope? Does an instrument exist that has a bipartite field like an anomaloscope but allows any combination of one or two monochromatic lights in each half of the field?    (answer)

What is colour? How is it detected?    (answer)

Does color affect the reflection of heat?    (answer)

Would CIECAM02 or CIEDE2000 be better at predicting spot color differences?    (answer)

How many colors does Munsell solid establish?    (answer)

Can mixed paint be measured while it is still wet? In our factory we mix paint, we want to measure it's color before painting parts.    (answer)

I would like to know if there is a way to determine the amount of ultraviolet light absorption by causing a change in the color of a particular substance and what the substance would be.    (answer)

I am trying to describe the colour of my sediment cores and have L*, a*, b*, and C* data from a spectrophotometer. I am looking for some directions on how to 'describe' the colour of my mud! Is there some tool or guide to convert numbers into a colour category?    (answer)

I painted a very pale yellow on one of my bedroom walls. I do not like the contrast with the country blue on the three other walls. Can I paint a brown that complements the blue over the yellow without affecting the brown color?    (answer)

I wish to have a white bedroom, where in the walls ceiling and floor are white. The windows doors and all wooden furniture will be painted white too. Kindly advise me on the suitability of the scheme. Should I be using stark white or would the use of ivory white be better. What should be the finish of the paint?    (answer)

Is it true that only some dreams are in color, while others are in shades of gray?    (answer)

Sign language interpreters have always been taught that they should wear colors that are in contrast to their skin tone to create maximum visibility and minimize eye fatique. Is there a more scientific way to teach these principles? What does research tell us about clothing color and eye fatique?    (answer)

I am trying to get the appearance of gold and silver on my monitor but they always look like yellow and silver. How do you get metallic gold on a monitor?    (answer)

How does one measure color of ink in its raw liquid form? I need to measure the color in that form. What tools are required? Are there standardised methods to sample ink to measure it?    (answer)

Somedays my eyes look green and other days they look more blue. What color of clothing or eye shadow would I wear to make them appear more green? What colors should I NOT wear if I don't want them to look blue?    (answer)

Each of our spectrophotometers has its own calibration standard. If all of the spectros are not calibrated to the same standard, aren't we calibrating in variation between the spectros? We can see anywhere from a .2 to over a .9 difference in our ΔE readings when we read the same areas of a sample on the different spectros. What would happen if we lost one of the standards since they are suppose to be unique to the manufacture of one specific specto?    (answer)

My customers set up the upper limit of ΔE=1. This a very difficult to match, and I've got the information that the human eye can't detect a deviation below ΔE=2. Which would you recommend to set-up? Also, what is the grayscale-measurement for plastic parts?    (answer)

I have read that a digital darkroom should be painted Munsell 8 gray. What should I tell my paint dealer so he can mix a color close to this?    (answer)

I have a paint is specified as Munsell colors and I need the RGB equivalents to display on my computer. Can you tell me the RGB for 1BG 6.3/1.4 and 4.6G 9.0/0.5?    (answer)

What is digital colour? The history of digital colour? Digital colour challenges? Problems encountered with digital colour?    (answer)

I've seen so-called UV energy beads change from white to various colors when exposed to UV light. What type of chemicals are embedded in those plastic beads, and are they toxic?    (answer)

I am testing whether colored (red and blue) backgrounds enhance or detract from a person's ability to assemble puzzles. Have these experiments like this have been done before? Any idea which age groups to test?    (answer)

I need a means to estimate the difference in general light reflection between walls in a windowless room painted matt magnolia (Munsell 10YR9/2), compared to matt brilliant white.    (answer)

What is the Reflectivity Index and what is the index for various colours, particularly silver?    (answer)

Blue colors wouldn't have to have higher UV reflectance than other colors and I am sure exceptions can be found. However, in general blue objects are reflecting highly in the short-wavelength end of the spectrum and that reflectance continues into the UV. Another way to look at it is that the wavelengths they tend to absorb are mainly longer than the the blue and UV wavelengths while other colors are largely absorbing the shorter wavelengths.    (answer)

Why does the color blue have higher UV reflectance properties than other colors?    (answer)

I am an artist, and I would like to display the color of the universe. Can you send me the RGB values?    (answer)

When I transform D65 illuminant values (in CIELAB) to RGB, I do not get R=G=B. Why?    (answer)

Various color systems (NTSC, SMTPE, CIE) use different white points. How are these defined?    (answer)

How precise are Munsell color sample meant to be read?    (answer)

Can you provide information on Ultralume U5000? Also, what are ΔE GE, ΔE Audi,and ΔE PQ?)    (answer)

Has research been done to determine how closely the color receptors in various species match what one might expect given their evolutionary environment?    (answer)

What are these devices: densitometer, spectrophotometer, and colorimeter?    (answer)

When driving at night, what colors on cars are easier to see and what colors are harder to see?    (answer)

Why was Munsell's colour system the most widely and globally accepted one?    (answer)

I want to scan the Ishihara plates and create the same colors on my monitor. Can you help?    (answer)

What is the equivalent RAL paint code for Munsell 3Y7.8/1.1?    (answer)

I want to write a paper on color measurement. Can you tell me the latest developments on this, and what we can do?    (answer)

I have a severe color vision deficiency. Can you help me modify images so I can see the world the way others do?    (answer)

Does color affect reflection of heat?    (answer)

To what degree is violet light magnetified to change into UV heat radiation?    (answer)

Can you help me separate Yu'v' values into Y, r-g, and b-y opponent channels for fourier analysis?    (answer)

Is there such thing as a perfect hue angle for Cyan and Magenta, in Lch?    (answer)

We design commercial kitchens with lots of stainless steel, white tile, and fluorescent lights. Why do our cooks prefer dark, mat finish tiles?    (answer)

What is LRV?    (answer)

What is the Pantone equivalent to color RAL 3020?    (answer)

I use a colorimeter that returns x,y,Y values. What units do they express?    (answer)

I have a densitometer that measures visual density. How do I convert the density values to CIE L*?    (answer)

Why are plants green. It seems they should be shades of black.    (answer)

I have a white printing on LDPE which is yellowing. How can I determinate the yellowing in a datacolor instrument?    (answer)

What is the differance in reflective properties between white and orange hard hats working in the sun? I know white reflects more but how much more does it reflect?    (answer)

In performing a mechanical task with several different colored backrounds, which colors would bring the most contrasting results in the efficency of which the task is performed?    (answer)

What is the maximum opacity for 1 micron thick white ink? is there a theoretical calculation?    (answer)

Is there a way to express Lch differences, in terms of units? (not referring to ΔL*, ΔC* or ΔH*) Hue for example is expressed in degree?s (eg 5°). What unit do I use to express the difference in lightness and chroma?    (answer)

The LAB values output by the GretagMacbeth Munsell conversion software are different than those I can input in Photoshop. Any solution for this?    (answer)

What is the best test for screening color vision in employees using penetrant fluorescent dyes to inspect manufactured metal items for defects?    (answer)

What is the best color to paint walls in a machine shop to enchance productivity?    (answer)

For color rendering/reproduction purposes, is it better to use a high-end CRT or LCD monitor for accurate color creation? What are the pros and cons of each system, and why have high-end CRT manufacturers discontinued their CRT products in favor of LCD?    (answer)

How can I transfer from Munsell notation to a single number indicator of overall color?    (answer)

I am working on matching a number of colours for plastic production. How do I convert my CIELAB values to colour pigments for production?    (answer)

What are the general norms for pale & pastel colours?Which are the colours (generic names) are considered as pale & pastel colours?    (answer)

If the fovea contains no S cones why don't humans have functional dichromancy in foveal vision?    (answer)

The freeware from gretagmacbeth.com cannot convert RGB values less than (34,34,34), the software tells me that the values are "Out of Munsell Range". Does Munsell support no color below (34,34,34)?    (answer)

How can I measure the color temperature of a image?    (answer)

How does the color pink affect the minds of males and females?    (answer)

Are you aware of an algorithm in the public domain for calculation of NCS notation from reflectance spectra?    (answer)

Can you give me a ballpark magnitude of color difference in ΔEcmc from monitor to monitor (crt) that one might experience?    (answer)

Which is the most appropriate measurement geometry for quantitative evaluation of metallic colors? What are the variables that impact the viewing conditions (size of sample, illuminant, surround, intensity) and is there any research that addresses this questions?    (answer)

Does the color of ice affect its melting rate?    (answer)

How do I get the value of Munsell renotation coordinates?    (answer)

Is there any standard Colorimetric values of this GSC (Gray-Scale Comparison Method) method used for visual assessment was used by Luo and Rigg?    (answer)

I am a geologist working with Munsell colour chips and need to know how accurate and precise manufactured chips are and how long they can be expected to last (i.e. before fading).    (answer)

Please explain to me what the Munsell Color Disc and Munsell Charts are. The discs used are: red (5 R 2.6/13), yellow (2.5 YR 5/12), black (N1), grey (N4). I need to measure the color of tomato paste by this method.    (answer)

Could you recommend a book that would serve as a good introduction to colour science for the lay reader? I am interested in learning the basics of colour science but am not a scientist or mathematician.    (answer)

Where I can find the exact value of Xn, Yn (the luminance factor for the illuminant or perfect white) and Zn?    (answer)

What's the minimum Δfreq or Δwavelength an average person can differentiate so as to recognize two different colors?    (answer)

Where I should look for for the energy distribution of commercially available sources?    (answer)

What is the best method (color space, sci vs. sce, degree observer, Illuminant,etc.) for calculating Light Reflectance Value (LRV) on a spectrophotometer?    (answer)

Why do we have color vision, and what is the evolutionary drive for color vision? It is striking how colorful the man made environment is compared to natural settings. What was the selective pressure that made individuals with color vision survivors-breeders in our natural habitat?    (answer)

Can you tell me the RAL Number which is most closely match with Munsell N9.5?    (answer)

How is color temperature of a monitor set to a particular temperature, say 6300k or 9300k? Is there any specific formula for this? How can I change RGB values of a particular temperature to anothertemperature? Is there is any concept of change in offset of R,G,B?    (answer)

How does color affect heat absorbtion?    (answer)

I am looking for color matching software for matching translucent materials. Are there any commercial packages that employ multiflux theory to aid in prediction and correction of CIELAB values as well as contrast ratio in formulations?    (answer)

When is white not white?    (answer)

Why is yellow the lightest color of the spectrum?    (answer)

How does the yellowing of the lens with age affect: colour vision, scotopic vision and the contrast of tests charts that are spectrally neutral?    (answer)

Where I can find the ultraviolet reflectivity index of various colors? How about the heat absorption index for various colors?    (answer)

In a chromatic adaptation transform, how can we measure the white reference of the incoming video signals?    (answer)

Is there a reference offering a method for the bi-directional calculation of densitometric quantities (particularly status M) and spectral transmittance to be used as weighting coefficients in the integration to solve for XYZ tristimulus values?    (answer)

What is the difference between perceptual colour gamut mapping and categorical colour gamut mapping?    (answer)

What is the basis for 18% reflectance being the center of the lightness scale in many different systems? For example: Munsell, Ansel Adams zone system, and CIELAB. Coincidence? I doubt it.    (answer)

How you can relate the color temperature to RGB values of video signals? Will the color temperature vary frame by frame or will it vary pixel by pixel of the signal? Can you give the mathematical equation by which color temperature and RGB values are linked?    (answer)

I measure animal colouration, in particular contrast, which is dependent on spot size, not just area coverage. I cannot measure the spots on a lizard belly, but I can get a numerical matrix from a digital photo. Can you help me calculate perceived contrast?    (answer)

Would you explain the meaning of ΔH*?    (answer)

Can visual color discrimination be taught? Does color discrimination become better through practice? What affect does the aging of a person's eyes have on color discrimination?    (answer)

What is the scientific termonology for when you fold a piece of fabric and two areas appear to be entirely different colors? I've seen this demonstrated: after folding, both sections of fabric appeared to be different colors.    (answer)

I need to find a way to measure the saturation and brightness of printed colors and pen ink. I need to select hues of equal brightness and saturation in my studies. Can you provide information about machines that can make such readings?    (answer)

I have used a spectrophotometer to analyse colour samples. How do you interprete the curves, for example prussian red, since there are many peaks shown?    (answer)

My technical director asked if I could find an "easy to understand" explanation of "CIE 2000." He may mean the CIE DE2000 mentioned in this publication. Is there a publication or expert that could assist us?    (answer)

Can you provide me a graph of grayscale Values (0-255) verses density? I need it to evaluate a grayscale calibration wafer.    (answer)

How can I specify a color so that manufacturers the world over will use the same color paint?    (answer)

Could you recommend a source for calibration tile standards for a camera-based color measurement system?    (answer)

How do I create a value Intensity scale illustrating three dimensions of colour? Could you define a cool and warm colour and whats a colour scheme? Could you give me examples of complementary, split-complementary colors?    (answer)

Where do I find a definition of the term CIEJab? I found the term CIEJab in the Microsoft Longhorn specification in their document "Gamut Boundary Description and Gamut Shell.doc"    (answer)

Did Munsell ever design and make public an eight-hue color circle? If not, such false facts are circulating on the internet. For example, see mauigateway.    (answer)

Why do painted walls of saturated complementary colors cause eyestrain when placed close to one another?    (answer)

In relation to Kodak absorption filter graphs; What does "Transmittance" & "Diffuse Density" mean? and the difference between them?    (answer)

Regarding the use of Kubelka-Munk theory and reflectance values, if I used the spectral reflectances for the Macbeth Color Checker, how do I determine the K and S values needed for the calculation (if I want to used the two-constant theory)?    (answer)

Outside my building, someone has spray painted the letters USAF with blue paint. The snow under the paint has melted putting the letters in relief. How come?    (answer)

A customer has asked for these colors: Light Green: 0.5G6.25/6.3 and 0.5G5.6/7.0 and 0.5G5.1/7.5, but I don't know how to translate it. He told me it's from Munsell and color is light green. How can I transfer to Pantone or NCS etc. to make a sample for him?    (answer)

Can I increase the opacity of a white Ink (at a given thickness) without affecting the color? I use TiO2. Are there other pigments that will increase opacity without affecting the whiteness index or CIELAB values?    (answer)

Digital image sensors (such as those used in digital cameras)use red, green, blue ink-based color filters to generate color. Do they therefore have a color gamut that limits the range of colors that they can detect?    (answer)

Do you have any training materials to illustrate color that I could use as an educational tool?    (answer)

I have made four boxes out of colored clear plastic and will be putting glass containers inside full of snow inside each one, then leaving them in the sun to see which melts faster. The colors are red, blue, yellow and clear. Can you help me find information on how color will make the snow melt faster?    (answer)

Can you provide spectral reflectance values for the Farnsworth-Munsell 100 Hue test?    (answer)

I need a teaching aid that uses three areas of colored cellophane (R,G,Y; or R,G,B) which is set on top of a background with text of different colors. How can I find the right cellophane and text color combinations that will allow the user to see only one group of text, while that same text is not visible through the other two cellophane colors segments?    (answer)

I am working on a digital conversion for raw files from RGB digital cameras. Can you assist me with a formula to convert floating point data from a digital camera into LCH space and help with transforming that space through a LUT to 4-channel printer separations?    (answer)

Is there an analytical method for calculating relative powers needed to achieve a specific white balance for monochromatic sources (eg: lasers) of known wavelengths?    (answer)

My spectrophotometer is getting old. I need a new instrument and software for evaluation and formulation of color paints and ceramics. What recommendations can you make?    (answer)

I have a reflectance spectrum of a soil sample. Can you help me convert this reflectance to CIE X,Y,Z and then to Munsell HVC?    (answer)

How can I determine the whiteness/blackness of CMYK inks?    (answer)

Can you help me convert from a Munsell color specification to a RAL color specification?    (answer)

I am developing a visual program to pick color harmonies of a color based on RGB values. Are there equations that could help me determine color harmonies?    (answer)

Would you explain what ΔE is and how is it measured?    (answer)

What is L-star?    (answer)

Why might the published measurements for Munsell neutral scale differ? For example, the reflectance values for the 1929 "Munsell Book of Color" are different in the 1933 Munsell et al article as compared to the 1940 Glenn article.    (answer)

What is the method for selecting the best combination of CMYK inks for a cmyk ink jet printer? What is the best way to determine the CMY values in order to get as large color gamut printer as possible?    (answer)

I do not have access to a spectrophotometer to measure paint reflectances. Where can I obtain the reflectance data for determining the Kubelka-Munk coefficients?    (answer)

I want to calibrate my monitor by eye. Are there color charts available for download that can help me do this? I require skin tone photo, color and gray scale patches.    (answer)

What is the established color difference tolerance for the plastics industry?    (answer)

What is a color management system?    (answer)

How should a color lab be designed? What colors should the walls and furniture be, so as not to influence the perception of color?    (answer)

Can you help me convert between RGB or CMYK and Munsell, CIELAB, or CIEXYZ?    (answer)

My two eyes see color differently. What causes this?    (answer)

What can you tell me about the blend mode algorithms?    (answer)

What are color vision deficiencies? How common are they?    (answer)

What is color?    (answer)

How do we see in color?    (answer)

What can you tell me about automotive paint pigments?    (answer)

What do we know about research done on colors & their meanings?    (answer)

What does it mean to be color normal?    (answer)

What parts of the eye are important for color vision?    (answer)

How do we select names for colors?    (answer)

How are cones organized in our eyes?    (answer)

What spatial and temporal processing takes place in the eye? the brain?    (answer)

What is chromatic adaptation?    (answer)

How do we characterize a person’s color vision?    (answer)

How many colors can we see?    (answer)



I bought a charcoal gray couch - love the color in the store. In my living room it looks dark blue! What color should I use on the walls and accessories to make it look gray again? (902)
To make something appear less blue (more neutral) you would need to surround it with objects that are even bluer. It is likely that the environment in your home (including the illumination) is more yellow than what you saw in the store and this makes your couch appear a bit more bluish through simultaneous contrast.   (Back to top)

Can fluorescent colors be printed with cymk printing system? I have Roland printer that uses eco-solmax inks. Are there any RGB or CMYK codes that will work? (901)
The only way to print fluorescent colors is to use fluorescent inks. While some CMYK inks might exhibit a bit of fluorescence, it is unlikely they are fluorescent enough to produce colors that we would typically call "fluorescent".   (Back to top)

In textile color matching, Is it possible to match target color in all light source without metamerism. If so what will be the possibility percentage? (900)
It is possible, but only when the spectral reflectance of the match and the target are identical. This requires that the properties of the textile substrate be the same and that the same colorants are used in the target and the match. If those conditions are met, then the probability of a spectral match depends only on the control of the coloring process. If those conditions are not met, then the probability of a spectral match is difficult to predict, but it would be quite low.   (Back to top)

What does a white balance actually do? (899)
It normalizes the RGB responses of a camera system to account for changes in the color of illumination. Ideally a proper white balance would result in R=G=B for neutral white and gray objects regardless of the illumination color.   (Back to top)

What makes a color bright? (898)
A color looks bright when it both reflects a lot of light and is very colorful. A white object under a lot of illumination will look bright, but a very colorful yellow object under a similar amount of illumination might look even brighter because it is colorful in addition to reflecting a lot of light.   (Back to top)

I study the topographic influence on snow. When an individual looks at snow in shadow, they are actually seeing blue light, yet they state they see white. Is this based on learned experience of color? What effect does the question have, i.e. "What color do you see", vs. "What is the color of the snow?" (897)
Great question! First keep in mind that color is a perception and not a physical property of light. There is a relationship of course, but it is not as direct as one might think. If they say the snow is white, then it is. The fact that a stimulus with more energy in the blue region of the spectrum (snow in the shadow) can still look white is due to chromatic adaptation. Our visual system adapts to changes in the color of the illumination and the result is that object colors like the white snow tend to appear relatively constant across the changes in illumination. Some observers can learn to separate the effects. Artists often do this and can distinguish easily between the color of the object (or material) and the color of the light reaching the eye.   (Back to top)

How does a flower´s color help it survive? (896)
The color attracts bees and other insects that pollinate, and therefor propagate, the plant. It also makes the flowers attractive to humans who then care for them and see that they survive to future generations.   (Back to top)

Many auto accidents happen in early morning and late in the evening when it is dark outside. Does the vehicle color have anything to do with this? What automotive paint color is easiest for the eye to see when it is dark outside? How about in daylight? (895)
I have not seen any statistics correlating car color with accident rates. Accidents are not common enough and there are two many other variables involved to get the required statistics. However, there is little doubt that visibility is one important factor in automobile accidents (this has been shown for motorcycle accidents since they are often "not seen" by other drivers). The most visible car color (and motorcycle helmet color for that matter) is white in low light conditions. This is because it reflects the most light and normally contrasts the most with the background (a snowy background would be an exception where a black car might actually be more visible). In general white is also most visible in the daylight because it contrasts most with the typical background.   (Back to top)

Although our sun is often depicted in artwork as "yellow", I have heard that it is actually "white", and that is why a white piece of paper appears white. Is this true? If so and we lived in a solar system with a different type of star, such as a red dwarf or a blue giant, would any objects appear "white", or would they take on the cast of their light source? (894)
Our sun is yellow in comparison with our blue sky. What looks white to us can be produced by a wide range of visual stimuli since our visual system is able to adapt to the color of the illumination. That adaptation is why a white piece of paper looks white under a variety of light sources (outside on a sunny day it is illuminated by the yellowish sun and the bluish sky together). If we lived under a sun of a different color, we would still adapt and objects would appear roughly the same as they do now (at least that white piece of paper would still look white).   (Back to top)

Imagine driving down a street toward a traffic light. How fast would you have to go so that the red light (700 nm) would appear green (500nm)? (893)
It would be approximately 2/5 times the speed of light. Faster than your car could go and stay intact. Sorry.   (Back to top)

Is there a way to measure gloss with a spectrophotometer or is it necessary to have a glossmeter? Is there a conversion between CIELAB values and gloss? (892)
You cannot convert CIELAB values to gloss as they are designed to measure the diffuse color and not the gloss. You can get some measure of gloss with an integrating sphere spectrophotometer by comparing the Y tristimulus values for measurements in specular included and specular excluded geometries. A diffuse sample will have no difference while a very glossy sample will have a difference on the order of 4% or so. It is better to have a gloss meter.   (Back to top)

How can I avoid metamerism? (891)
Metamerism cannot be avoided since it is really a property of the human visual system. Metamerism refers to the fact that two colors do not have to be identical in spectral power distribution in order to match in perceived color. You are probably thinking of illuminant metamerism in which two samples match for one light source (a metameric match in which the spectral reflectances differ) and do not match for another light source. The only way to avoid that is to produce spectral matches. (Sorry.)   (Back to top)

What are L* a* and b*? Are they constants? If not, how can I find those values? (890)
L*, a*, and b* represent the lightness, redness-greenness, and yellowness-blueness dimensions in the CIELAB color space. The values are not a constant, but rather are different for every object and illumination condition. They are found by measuring the spectral reflectance of materials (or spectral radiance of self-luminous stimuli) and doing some colorimetric computations. I would recommend a good introductory text on color measurement like Berns&apost; "Principles of Color Technology, 3rd Ed." to get a good overview of the CIELAB space.   (Back to top)

Where can I find calculator or software for LRV? (889)
I don't know of a specific LRV calculator or software, but it appears that LRV is the same as the CIE Y tristimulus value which is readily obtained from color measurement instrumentation.   (Back to top)

We are told that Red, Yellow, and Blue are the "primary" colors, and that you can make all other colors from them, but those 3 can´t be made by combining the others. In additive systems, it is red and green that combine to make yellow. Is there something inherently special about red, yellow, and blue, or are they considered "primary" only in the sense that the most basic medium of color manipulation is a subtractive system? (888)
They are but one set of subtractive primaries and red, green, and blue are the typical additive primaries. There is nothing special about them. Primaries are simply three lights (additive) or colorants (subtractive) that can make a range of colors and chosen such that none of them can be made by a mixture of the other two.   (Back to top)

When we compare luminosity of different hues, we find that blue is a relatively dark color, and yellow is a relatively light color. Do hues have an inherent luminosity independent of human perception? (887)
No. It is due to the spectral response of the human visual system. Anything you see in a rendered black and white image is caused by the spectral response of the imaging system ... which is often designed to mimic the human visual system.   (Back to top)

I am trying to emulate a smaller-gamut RGB color space on an LCD display using a 3x3 matrix, and I can not seem to figure out the general-purpose way of doing this. You reference Poynton´s book in a similar FAQ but he skips over the process and just spits out the answer for some important cases. (886)
You might try Berns´ "Principles of Color Technology, 3rd Ed." to get a more illuminating explanation. It is hard to explain it all in a short response, but you need to first linearize your RGB values, then convert to XYZ with an appropriate 3x3 matrix, then convert to the new (smaller gamut) RGB values with the appropriate 3x3 (this one will be different from the inverse of the first or you will make no change) and then do any correction for display nonlinearities (e.g. gamma).   (Back to top)

Is there is a device that can measure liquid gravure ink spectral transmittance? I need a method to confirm ink recipe components in a liquid ink sample. I could use a faster option than the traditional draw-down proofing method. (885)
Many spectrophotometers are capable of measuring the transmittance of liquid samples placed in a glass cell. You can inquire with instrument manufacturers to get an instrument with appropriate capabilities (or find out if you already have one). The only question would be whether the inks are transparent enough to allow a measurement. If they are translucent (scatter light), then the measurements might prove difficult.   (Back to top)

How many lights are metameric to white light reflected from a paper? (884)
There is no limit to the number of metameric lights that could be created.   (Back to top)

I use the Munsell Color Books to develop color harmonies for clients to use on short term projects. Is there an inexpensive way to get swatches or chips that match the Munsell notation? Can I print them? (883)
You can get authentic Munsell chips from X-Rite (they sell all Munsell products), but they are not particularly inexpensive. It would be difficult to print them accurately. I would suggest using some inexpensive samples such as the Coloraid papers and then using your Munsell books to visually determine a Munsell designation for the various samples. That would probably be the most cost effective method.   (Back to top)

Are there studies of floral arrangement preferences of dichromats? (882)
Unfortunately I am not aware of any such studies. However, you might want to look at the website vischeck.com. It allows you to upload images and then see what they might look like to people with color vision deficiencies. While the rendered colors might not be accurate, it would at least let you see which colors become indistinguishable. By testing some images of floral arrangements you would be able to see if the various flowers contrast more or less, etc.   (Back to top)

How did the CIE 1931 color matching experiments evaluate the whole gamut when we know that the RGB color gamut is a subset of that of the human eye? In other words, we know there are colors that cannot be matched by the RGB lights. How did they get around this? (881)
It is really quite easy. RGB primaries are/were used and there are certainly many spectral colors (monochromatic lights) that cannot be matched by positive amounts of RGB. (The number depends on the selection of RGB.) The key here is the word positive. What is done is that the light to be matched is desaturated with one of the RGB primaries and then that desaturated light is matched using the other two. For example, 500nm is a saturated cyanish wavelength that is outside almost any RGB gamut. What is done is that it is mixed with a little bit of R and that mixture is matched by a combination of B and G as follows.

500nm + R matches G + B

Grassmann´s laws tell us that additive color matches follow simple algebra (that´s why the whole system works at all) and that allows us to subtract the amount of R from both sides of the match resulting in

500nm matches G + B - R

Thus, we can have negative amounts of light to match every possible color. That is why plots of the color matching functions in terms of RGB go negative at some wavelengths. (Note: For clarity I have left out the distinction between the amounts of RGB and the definition of them ... essentially, I left of the units.)   (Back to top)

The sensitivity of the human eye to color difference is greatest at approximately 550 nm. However, in interpreting the MacAdam ellipses , it would appear that humans are least sensitive to differences in color in this region. Why? (880)
Humans are most sensitive to light at 555nm (when using their cones), but that is a response to seeing, or not seeing, a light stimulus at all, not to distinguishing a color difference. It really is pretty much impossible to say what color people are most sensitive to since any measure would depend on the color space used. MacAdam ellipses in xy are definitely not the way to go. First they represent the results of only a single observer and second they are just showing the non-uniformity of the xy diagram, which really has no direct physiological significance with respect to color discrimination.   (Back to top)

I measure timber colour using a Minolta Chromameter CR-400. I want to compare my values with those of other woods whose colors are listed in percent Luminance, Dominant wavelength (λ)and percent purity. Can I convert these values over to CIELAB? (879)
You are in luck. The computation is possible, but it is a little tricky. First, the % luminance is your CIE Y tristimulus value. Dominant wavelength and purity are directly related to the CIE xy chromaticity coordinates. Dominant wavelength is the wavelength at which a line from the white point (xy) through the sample (xy) intersects the spectrum locus on the chromaticity diagram. Purity is the fractional distance from the white point that the sample lies in the xy diagram. In other words, the dominant wavelength and white point define a line in the chromaticity diagram and the purity defines where on that line the sample falls. That would allow you to get xy chromaticities for your samples. Then together with Y (% luminance) you can convert to XYZ using the following.

X = Y(x/y)
Y = Y
Z = Y((1-x-y)/y)

With XYZ you can compute CIELAB coordinates. I would recommend you refer to a colorimetry text to get all the necessary details. Purity and dominant wavelength are discussed on p.61 of Berns Principles of Color Technology, 3rd Ed. You can also get all the details and a great reference book in Wyszecki & Stiles Color Science.   (Back to top)

Is it possible to scientifically determine the original colors in an old black and white stereoview photograph if some of the colors are known? (878)
Unfortunately, no. You might be able to make some good guesses based on the objects in the photographs, but color is three dimensional and in a black and white photograph it is mapped into one dimension. So, for example, a light red and a dark blue might map to the same gray level in photograph and you have no way to tell which color the object was without some additional information from outside the photograph. And unfortunately, knowing about some objects does not tell you about others.   (Back to top)

How does aging affect color perception? Are older people able to discriminate brighter colors or softer colors better? (877)
As we age, the lens in our eye begins to absorb and scatter more blue light (it becomes yellower). This causes a decrease in visual sensitivity to shorter wavelengths that make us less sensitive to blue colors and less able to discriminate purple and red colors. There also tends to be more of a negative effect of glare as we age. So really, no colors are discriminated better as people get older and whether brighter or softer colors are preferable would probably depend on the particular person and the illumination and viewing conditions.   (Back to top)

What wavelength(s) are used in the calculation of Gardner color? (876)
The Gardner Index is computed from CIE chromaticity coordinates (Yxy) and is therefore based on the entire visible spectrum of wavelengths from approximately 380nm to 760nm.   (Back to top)

Is it possible to explain color to a blind person if thay have never experienced it? Can the brain of a blind person assign a color to something if they know the shape but not the color? (875)
We can not say for sure, but I would think this would be impossible. It is very difficult to describe colors of objects to a seeing person and all of the definitions of color use examples. If one has never experienced the examples, then it seems it would be extremely difficult, if not impossible, to give them an impression of color appearance.   (Back to top)

I need to predict CIELAB of a color at different thickness. The color is transparent and .01 inches. How do I predict LAB values at thicknessof .121? (874)
It can be done if you have the spectral transmittance data for your material. It cannot be done from the CIELAB values alone. You would basically want to use the Bouguer-Beer Law that relates the transmittance of a material to the colorant concentration (fixed in your case) and the thickness. In the simplest terms, for each doubling of thickness, you square the spectral transmittance. However, you should look at the details in a textbook such as Berns Principles of Color Technology, 3rd Ed. (pp. 157-161). This is sometimes referred to as simple subtractive mixing.   (Back to top)

Why do different pure hues have differing lightness values? (873)
The perception of lightness is complicated and depends on many variables. However a simple way to look at this question, that does explain most of what is observed is to think about our relative sensitivity to light of various wavelengths through the visible spectrum. In general we are more sensitive to wavelengths in the middle of the spectrum (approximately green) than to those at the ends (approximately blue and red). A pure green hue will be made up of light that we are very sensitive to and thus generally have a higher lightness than a pure red, blue, or purple (which is made up of red and blue). Of course it is possible to create stimuli that do not follow this trend, but for reflecting objects, or lights with equal amounts of energy, this general rule will hold. Usually highly saturated greens and yellows have a relatively high lightness, while reds, blues, and especially purples have a relatively low lightness.   (Back to top)

In his 1943 OSA paper "Specification of Small Chromaticity Differences" MacAdam describes constants g11, 2g12, g22 and gives values for them in graphical form. Is there a source for this data in conveniently tabulated form? (872)
The data required to compute the ellipses can be found in tabular form in Wyszecki & Stiles' "Color Science" book. They provide orientation angles and axes lengths rather than the gij coefficients, so it might not be exactly what you are looking for, but it is a commonly used source for this information. As you are using the ellipses, be sure to keep in mind that they represent data for only a single observer!   (Back to top)

I need a device that will give me color readings at an observer angle of around 45 degrees or so that will pick up almost 100% specular reflection. (871)
You are correct that most color measurement instruments are designed to measure angles away from the specular reflection. There are gloss meters that measure the specular reflection, but they do not measure color. To do both you need a goniospectrophotometer that measures spectral reflectance at any combination of illumination and view angles. Murakami makes one such instrument and here is a link to some information from the US distributor.   (Back to top)

Why is it not possible to get an accurate ΔE colour measurement on a metallic powder coating? (870)
It is possible, but the result is limited to the geometry of illumination and view present in the spectrophotometer. Metallic materials exhibit geometric dependencies in their color that are not easy to capture and represent with spectrophotometric measurements (and therefore ΔE*). Sometimes such materials are measured at several combinations of illumination and view angle to try to characterize these properties. The other potential limitation is that the metallic highlights have reflectance factors that significantly exceed those of normal reflecting materials and this results in CIELAB coordinates outside the normally well-understood range (e.g. L* can be much greater than 100). While such values can be computed and used in a ΔE* calculation, the meaning of such values remains very uncertain.   (Back to top)

At what luminance (Candela per meter squared) in the ambient environmental light does scotopic vision turn to mesopic vision, or at what point can we start to see color? And at what point can we see the majority of colors? (868)
The specific answer would depend on the individual observer, viewing conditions, and the state of adaptation. However at approximately 1 cd/m^2 the responses of rods and cones are equal, so this is essentially the midpoint of the mesopic region; some color is visible. As a rule of thumb, you could assume that reasonably good color vision (majority of colors) is present at 10 times that luminance (10 cd/m^2) and that no color vision is present at 10% of that luminance (0.1 cd/m^2).   (Back to top)

What is the most common first color that children recognize? The second? (867)
I don't think I can answer any better than this website. Vision works on contrast, not individual colors. The first is light-dark contrast, so you could say that infants can see white, black, and grays first. This is probably followed by red-green discrimination and then yellow-blue discrimination.   (Back to top)

We have a WWI aircraft we are recovering with fabric that requires a dark green paint for the wings. This aircraft is flown a lot and displayed to the public outside quite a bit. The problem is that this paint absorbs sunlight heat dramatically which reduces the life of the doped fabric, causing it to shrink prematurely and it is fairly expensive to replace. Would a primer coat of silver dope or white help reduce the absorption of the heat into the fabric under the dark green paint? (866)
Unfortunately that won't help since the dark green will have already absorbed the light and converted it to heat (a temperature increase). The white or silver layer would only work if it was exposed to the light and then, of course, your plane would be white or silver instead of green.   (Back to top)

Do you know the origin of a measurement called the "flop index", which is defined as flop index=2.69(L15°-L110°)^1.11/((L45°)^0.86). My Xrite M68II reports this metric, however, X-Rite does not explain the source of this equation. Do you know where I might find the source of this equation, or another good way to mathematically explain the color difference at several angles? (865)
Unfortunately I cannot find a source for this, or any, flop index equation. It appears to be some form of empirical fit, so there must have been an experiment done somewhere. I would suggest you contact X-Rite to see if they can provide a source for the equation. This particular equation only depends on L* (measured at various angles), so it is only telling you about lightness differences. If you are interested in full color differences, you can compute normal CIELAB ΔE* color differences across the view angles. You might get some unusual values in comparison with color differences computed within a single geometry, but with care, the computed values could still be useful.   (Back to top)

What is the differance between additive color and subtractive color? (864)
There is no difference in the colors themselves, the difference is in how they are produced. The following answers come from WhyIsColor:

Q: How does additive color mixing work?
A: Additive mixing happens when two or more light sources are superimposed by either illuminating the same spot or by being so close together in space and time that oure visual systems cannot distinguish them. What we perceive is the sum of the energy from each of the lights. This is how computer displays and televisions reproduce color. Red, green, and blue are common additive primaries since it is easy and efficient to makea wide variety of colors with them.

Q: How does subtractive color mixing work?
A: Subtractive mixing happens when two or more dyes or pigments are combined by either layering or mixing them. Each dye or pigment absorbs certain colors (wavelengths) and what we perceive is the light that remains after each colorant has absorbed its part. This is how some printing systems and paint mixtures produce various colors. Cyan, magenta, and yellow are common subtractive primaries since it is easy and efficient to makea wide variety of colors with them.   (Back to top)

I am turning my formal dining room into an art gallery. We painted today and it is too bright. The way it looks now all you will see is the paint color and not the art. What are the best colors to paint a gallery, given that all the pictures are of different color schemes? (863)
The best colors for walls tend to be of medium lightness (perceptually half way between white and black). That way both the light and dark areas of the artwork can contrast with the background. Theoretically, the ideal color is also a neutral gray, but that can become monotonous, especially in a home. The selected color is not nearly as important as the lightness, but it is best to avoid any very saturated colors. Pick a color of medium lightness, that is a hue you like, but not very saturated.   (Back to top)

Scientifically speaking, is black a color? Is white a color? (862)
There is no question that black and white are colors.

The technical definition of color that is internationally agreed upon includes them as colors and, specifically, there is a definition of achromatic colors as follows: "A color lacking hue; white or grey or black".   (Back to top)

In comparing light bulbs based on their color temperature, how much difference in color temperature is needed before an average person can notice that difference? (861)
It would depend on the viewing conditions. For example, if the two bulbs were viewed side-by-side, then a smaller difference would be perceptible than if the bulbs were viewed one at a time. However in general, it is probably reasonable to assume that a difference of about 100K or greater is perceptible. (The actual value will also depend on the initial color temperature as well with the change required to see a difference becoming larger at higher color temperatures.)   (Back to top)

Are there any specific details in 45:0c reflectance measurement, such as the effect of distance between detector and sample or distance between light source and sample? Are there restrictions on the circumstances, like the color of the floor on which we put our sample? (860)
The specifications are in CIE Publication 15:2004. They include restrictions about illumination and view angle and solid angles, but nothing about distances. They also do not restrict the backing of the sample, although you might want to be careful of that if the sample is such that light might pass through.   (Back to top)

Is there any approximation to convert between Hunter Lab (illuminant C, 10 degree observer) and CIELAB (illuminant D65, 10 degree observer)? (859)
There is no unique solution since there are many spectra that can produce a given set of colorimetric coordinates (metamerism). You could make a rough approximation by using the inverse HunterLab equations to convert back to XYZ tristimulus values and then compute the CIELAB values for them (perhaps just using Ill. C since it is close to D65 and this will be only an approximation).   (Back to top)

I received data from two sources. The first measured Hunter Lab on light source C under 10 degrees, the second measured CIELAB on light source D65 under 10 degrees. I don't have the spectra. Is there any approximation with which I can convert between them? (858)
There is no unique solution since there are many spectra that can produce a given set of colorimetric coordinates (metamerism). You could make a rough approximation by using the inverse HunterLab equations to convert back to XYZ tristimulus values and then compute the CIELAB values for them (perhaps just using Ill. C since it is close to D65 and this will be only an approximation).   (Back to top)

What observer for XYZ values can be used in CAM02, 2 degree or 10 degree? Some articles use 2-degree observer, the others use 10-degree observer. (857)
CIECAM02 was derived using the CIE 1931 2-deg. color matching functions, so they are the best choice. However, it will still work well with 10-deg. tristimulus values but the results will not be identical.   (Back to top)

I am looking for the differences between red, blue, green, and yellow dye. Can you tell me anything different about them, other than they are different colors? (856)
The dyes will have difference chemical structures that cause them to interact with light differently. For example, a yellow dye absorbs blue light while a blue dye does not absorb that light, but would absorb green and red light. It all comes down to the chemical structure.   (Back to top)

What part of the spectrum helps grass grow? (855)
Chlorophyll in the plants absorbs light and converts that energy into the forms required for the plant to grow. Since chlorophyll is normally green, it is mainly the blue and red wavelengths in the visible spectrum that would be most strongly absorbed to provide this energy. However, a significant amount of ultraviolet energy is also utilized by the plant and even some of the green light is absorbed.   (Back to top)

Why does the color of a crayon or colored pencil look a different color on paper? For example, some purples show up blue on paper. (854)
Because the colorants in the crayon interact with the paper depending on the amount of wax you put down (how hard you press) and the lighting. It is possible to make a wide variety of colors using a single crayon. As more wax is applied to the paper, the color should begin to look more and more like the crayon itself.   (Back to top)

Would a spectrophotometer be able to accurately read the color differences between chrome plated surfaces? (ie. mirror-like finish) What settings or type of instrument would best achieve this? (853)
Yes, but it would take a special spectrophotometer designed to measure the specular (or regular) reflectance, which is the main component in a chrome surface. You could probably get a reasonable measurement from an total reflectance geometry (integrating sphere with specular component included), however their might be differences in the geometric distribution of the reflected light that would be masked in that measurement so you might also want to include an SCE measurement as a second confirmation. It is a challenging measurement, but with some care you might be successful.   (Back to top)

Is it possible to quantitatively describe a color just by its reflectance or radiative spectrum? (852)
Perceived color depends on the reflectance of the object (or the radiance of a source), but it also depends on the illumination, the viewing geometry, and the response and adaptation of the human observer. The spectral properties alone are not enough to fully describe a color.   (Back to top)

How a mixture of R, G & B single wavelength sources (such as RGB laser) can produce white light even though they do not cover the whole spectrum? (851)
Three appropriate lasers are sufficient to stimulate the three types of cone receptors in our visual system to the same degree that they would be by a continuous spectrum. Thus, we are not able to perceive the difference. This property is known as metamerism.   (Back to top)

Is there a formula for calculating Delta E in Munsell? (850)
This person answered their own question before I got to it, but It seems worth pointing out the Nickerson Index of Fading on our FAQ. Here's what she wrote...

"Hello Dr. Fairchild,
   : I've submitted another questions to your wonderful "Ask a Color Scientist" page, but I thought I would also send a note to you on the same topic, but with a bit more detail.
   : I am looking for an easy color difference formula for Munsell. I know that it won't be as spot-on accurate as the advanced formulas used with more modern color spaces, but that's OK, I want something that is generally reliable, and that will be good enough.
   : I've done a bit of Googling on this and the only thing that I have found is the 1936 Nickerson "Index of Fading" formula:
   : ΔE = 2/5CΔH + 6ΔV + 3ΔC

Where H/V/C are Munsell coordinates.   (Back to top)

I would like to convert from CIELAB coordinates into the approximate spectral red green and blue component curves. Is this possible? (849)
It's not really possible since a given set of CIELAB coordinates can be produced by an essentially infinite variety of spectral power distributions. The only way this problem can be solved is to assume a limited form of the spectral curves and then compute mixtures of those properties.   (Back to top)

Why do we see colors when we spin a disc that contains figures in black & white? (848)
These colors are referred to as Benham's colors or Fechner-Benham colors. Here is a nice explanation of the Benham top. Also, if you do a web search on those terms you can find a lot of information and theories.   (Back to top)

When job requirements demand color discrimination, how often should employees be tested on their color perception? (847)
A person's overall color vision (normal vs. defficient) rarely changes in their lifetime. However color discrimination ability might. So everyone should be checked at least once and it is probably reasonable to repeat the tests every few years, but not really necessary to do it more often than that.   (Back to top)

Is there a color model which would allow me to do the following? Given L*a*b*/XYZ/whatever coordinates of a color stimulus, given specified viewing conditions and color, what is the shape/size of the JND "ellipsoid" around the color, and what are the directions of the hue/chroma/lightness axes? (846)
The CIELAB color space would be your best bet as a starting point. The L*a*b* rectangular coordinates can be converted into L*C*h cylindrical coordinates to represent lightness, chroma, and hue angle respectively. Predicting the size and shape of JND ellipsoids is another matter that is a bit more complicated. You might want to look into the CIE2000 color difference equations to understand the relationships between color difference perception and appearance specification in CIELAB.   (Back to top)

Is there still a copyright on the Munsell color system? If so, who owns it? (845)
X-Rite currently produces and sells Munsell products. The colorimetric coordinates of the colors have been published, so the colors themselves are not copyrighted. However, it is likely that X-Rite does have the various products protected by copyright. It would be best to check with X-Rite.   (Back to top)

Which light colors are absorbed by a yellow tulip? (844)
Blue.   (Back to top)

A one dimensional halftone cell has 50% coverage with reflection density 2.0 and 50 % coverage with reflection density 1.0. How is L* calculated for this cell? (843)
You first need to convert from visual density, D, to luminance factor, Y for each cell. (Y = 10^-D). Then you would average the two Y values (since both are 50% coverage, otherwise you would do a weighted average according to the areas) to get the overall Y value, which is then plugged into the L* equation.   (Back to top)

Are you aware of any software packages or even just charts, that list Munsell colors by both code and name? (842)
I can't vouch for the the completeness or accuracy, but I have found an online table of the ISCC-NBS color naming system with Munsell designations. It might be helpful for you.   (Back to top)

What colors (in order) would best absorb a green 529nm laser light? (841)
You haven't provided enough information to answer that question. You would need the spectral reflectance of the material (or transmittance if it was not opaque) for each color and then you would just order them from least reflective to most. For example, a black object would absorb almost all the energy at any wavelength, but a red material might well absorb even more at that particular green wavelength. You can't tell from just the color names.   (Back to top)

Could you please tell me if there is any function that computes the chromatic adaptation and the color appearance for the various types of color deficiencies? (840)
I am not aware of any models specifically designed to compute chromatic adaptation and color appearance for color deficiencies. The closest I can think of is the model implemented and described at vischeck.com. While it does not produce predictors of appearance, one might take the simulated output of their model as calibrated RGB input into a color appearance model such as CIECAM02 in order to obtain approximate appearance.   (Back to top)

How could I provide (or display) the approximate color of a star given it's Kelvin temperature? (839)
Here's a website that describes how to approximate various color temperatures in sRGB.   (Back to top)

I am interested to convert a hex html or decimal rgb value to cie 1931. How can I do this? (838)
You might try easyrgb.com.   (Back to top)

Is 0.05ppm a suitable tolerance for measuring absorption on a spectrometer for beverages? When is it no longer a visible difference to the naked eye 1ppm, 0.1ppm, 0.01ppm, etc? (837)
This would depend on what color the beverages are and what you are measuring. The only way to evaluate visual tolerances is with colorimetry, PPM on spectral absorptance functions tells you very little (perhaps nothing) about visual perception.   (Back to top)

What is the best color to paint behind a High Defintion tv mounted on the wall? (836)
The best thing to have back there is a little bit of light that doesn't fall on the front screen (therefore washing out the image). If the lights are off in the room, then a small light behind the TV is helpful. This lightness helps to increase the perceived contrast of the display over what you see in a completely darkened room. If the room is illuminated, a light grey is probably the best choice. Light, but not too bright like a white, and neutral to not bias the color perception of the display.   (Back to top)

What dyes are mixed to get Dark Shell Gray? (835)
I'm sorry but that's really impossible to answer for a couple of reasons. First, color names are generally not defined precisely so "dark shell gray" could be a wide range of colors. Second, the dyes used would depend on the type of materials being used to make the color and even within a single material type it is possible to make the same color with many different combinations of colorants.   (Back to top)

I am a retinal surgeon. We sometimes stain the retina with trypan blue in order to highlight superficial membranes that need to be peeled (over the retina). Is there a colored contact lens that I could wear that would highlight the blue spectrum more so that it would be easy to see faint staining on trypan blue on the retina? (834)
If you are trying to see a light blue on a pale background, then the best thing to do would be to use light that is absorbed strongly by the blue, but not by the background. That would be yellow or red light (which would also be reflected strongly by any red tissue). You can accomplish the same effect with either lighting or lenses, although it might be a little easier to discriminate by briefly changing the color of the lighting since you won't adapt to the color change as much as you would wearing colored lenses.   (Back to top)

I would like to come up with a color scheme that assigns an absolute color value to common color words. In this scheme I would want scarlet to have a distinct and absolute value different than crimson or puce. Is there any site or program that has assigned absolute color values to the English names of colors? (833)
For this purpose, I would highly recommend the "ISCC-NBS Dictionary of Color Names". It is well out of print, but used copies can still be found online and in libraries. It provides Munsell designations for a wide collection of common color names. However, you should be aware that color names are very imprecise and there is a range of designations for each name. It is quite likely that scarlet and crimson will have some overlap.   (Back to top)

We measure several prints for our printer characterizations. Two questions: (1) what is best space to average - spectral reflectance, LAB or XYZ and (2) if we wanted to do a weighted average to reduce the weight of data which tended to be "inconsistent", how would we best do that? (832)
There is no single "correct" answer. If you are interested in color appearance, then it makes most sense to average in a perceptual space like CIELAB. If you are interested in the physical characteristics of the printer, then it makes more sense to average in spectral reflectance. (However it would make even more sense to average in toner amounts after deriving an accurate model of the printer!). For color applications, CIELAB is probably the best choice. To do a weighted average, you could compute color differences from the mean measurement for each color and then recompute a weighted mean using a weight that is inversely proportional to those differences.   (Back to top)

In the CIELAB color space, what is the approximate difference for each of L*, a*, b*, and ∇E that most people would not percieve as a different color. (831)
It depends significantly on the color in question and the viewing conditions and could range anywhere from less than 0.5 to as much as 3 or 4 units. The general rule of thumb is about 1 CIELAB unit.   (Back to top)

Are there guidelines or rules of thumb for how colors are perceived as "dominant" in an image? Are there differences in the perception of color dominance among different colors? If so, how is this described in the CIELAB color space? (830)
I am not sure what you mean by "dominant", but it would likely be the colors that occupy most of the image area and would probably be defined by hue (as in ... there is a lot of orange in that image). I don't know of any algorithms, but I would suggest looking at a histogram of hue angle in CIELAB and finding any dominant peaks. You might also search for the "Color Reproduction Index" that was published by Pointer and Hunt which does a similar division of colors.   (Back to top)

Where can I find a chart showing color names, the colors themselves and CIELAB color coordinates? Ideally, this would also show the RGB color coordinates. I have found many RGB charts like this but none with the CIELAB coordinates. (829)
I don't know of any since it is a very difficult procedure to calibrate such a chart and RGB coordinates are generally undefined. I would suggest taking one of the RGB charts you have found and performing a conversion from sRGB values to CIELAB values (along with viewing them on a calibrated display).   (Back to top)

Are there established color values for the color of skin for various ethnic groups (like Lab or Munsell for example)? This is for a makeup manufacturer who wants to design packing for specific groups of people. (828)
I am not aware of any specific standards although some might exist. You might look at some of the color imaging test charts (e.g. the Munsell Digital ColorChecker SG from X-Rite that has several skin-tone samples, see this web page to get an array of reasonable colors.   (Back to top)

I dyed 100% cotton red, yellow and blue and placed them in direct sunlight for a week. The red appeared to fade the most, but I can't explain why. Can you help? (827)
It's hard to say since it depends on the specific colors and how you measure "fading". The yellow one wouldn't look like it faded much because it is hard to see yellow fading toward white (they are already similar colors) and the red one might have faded more than blue because it is absorbing more blue light, which is made up of the shorter wavelengths, which have more energy and tend to cause more chemical changes such as fading.   (Back to top)

Why does red disappear when viewed behind red glass? (826)
It actually doesn't disappear at all ... it still looks red doesn't it? What happens is that red text (or other patterns) on white backgrounds disappear since the red glass makes the white background appear red as well and no contrast remains. If the red text or pattern was on a black background, it would remain just as visible through the red glass.   (Back to top)

Are grey shades actually constant, because they are nearly achromatic, or is there something about eye biomechanics that create a visual perception not in agreement with spectral readings? (825)
Grays, like any colors can be very color inconstant. It really depends on the combination of reflectance characteristics, light sources, and observers. The most likely samples to be nearly constant would be grays with flat reflectance curves (known as nonselective materials). However, even those are likely to not be perfectly color constant.   (Back to top)

I need to know the Munsell color for 'school bus yellow.' The unsourced quote I have says it is 9.4YR, 7.5/9.2. (824)
I'm sorry, I don't have the standard in terms of Munsell coordinates, but the Yxy values are 40.2, 0.4882, and 0.4205 respectively (From Color Standard SBMTC 008, 1997). Your Munsell coordinates seem about right, but I can tell from the Y value of 40.2 that the Munsell Value should be 7 instead of 7.5. The rest can be converted using the Munsell Conversion Freeware available from X-Rite. Unfortunately that won't run on my computer!

Update!
From The Physics and Chemistry of Color:The Fifteen Causes of Color. Second Edition by Kurt Nassau. John Wiley & Sons, Inc. 2001 p 395: "A full designation for an orange-yellow school bus in the sequence H V/C and using interpolation might then be 9.4YR 7.5/9.2."   (Back to top)

What does LCC stand for in the color science world? (823)
To my knowledge, it stands for nothing. I did a little online searching and found a few references in patents to an LCC color space as a "luminance-chrominance" space. It appears the term might be used in a generic sense to refer to "any luminance chrominance space".   (Back to top)

Where can I purchase a poster size print of the CIE 1931 Chromaticty Diagram? I realize that the diagram is only a 2D projection of 3D matching data however I still find it useful to illustrate some of the other attributes of the data depicted (color mixing, color temperature, color gamuts)? (822)
Not only am I not aware, but I probably wouldn't tell you if I was!

Seriously, we really don't like them because they badly misrepresent the meaning of a chromaticity diagram. The diagram tells us nothing about color appearance since it is only based on matching data. It only tells us whether two colors match, but not what color they appear.   (Back to top)

At what distance, target size and viewing conditions (illumination level/type) does the HVS's ability to resolve color breakdown? Put another way, what is the "chromatic" resolving power of the HVS and how is that defined in terms of distance, size, viewing conditions? (821)
In your observed scene, there are two things happening. The stimuli are getting smaller, but they are also becoming physically more similar due to the intervening atmosphere. If they were far enough away, all you would see is atmosphere (or imagine the atmosphere was more optically dense, like on a foggy day) and you couldn't discriminate them at all. So, first of all, that physical change needs to be accounted for. After that, there are changes in your visual system as well. Viewing conditions make all the difference in the world and cannot be explained in a short answer (I wrote a whole book on that entitled "Color Appearance Models"). However, as the stimulus becomes small in viewing angle, you do lose your ability to distinguish color. Once the stimulus is smaller than about 0.25 deg, you are close to becoming a dichromat (it's called small area tritanopia) due to the small numbers of blue-sensitive cones. Then when it gets even smaller, maybe 1-2 minutes of arc, you really can't discriminate color at all (only brightness). This is why stars look far more colorful in images than they do to the naked eye (even those that are bright enough to see with cones).   (Back to top)

Is black a natural color or is it just a very dark brown that people just see as black? (820)
Technically, color is defined as a perception, so if something appears black to you, it is black. Beyond that, there are many naturally occurring materials that we would consider to be black (not just dark brown or other color). Obsidian is one thing that comes to mind (although it does occur in colors other than black as well). So, yes, black is a natural color.   (Back to top)

We would like to know the complete Reflectance Measurement principle and formula for the dual beam color spectrophotometer including Light trap, PTFE standard and sample. (819)
I would suggest texts like Berns' "Principles of Color Technology, 3rd. Ed." for a fundamental introduction and Wyszecki and Stiles' "Color Science, 2nd Ed." for more details and references.   (Back to top)

Is there a relationship between visual lightness (when we judge lightness of color) and Light Reflectance Value (a measurement that is expressed mathematically? (818)
Yes, they can be related mathematically. One way is through the CIELAB L* equation. L* is intended to represent perceived lightness (your grayscale judgement) with a perfect white at 100, a perfect black at 0, and a perceptually middle gray at 50. It is a function of the Y tristimulus value, or luminance (which is also your LRV). That perceived middle gray with an L* = 50 has Y = 20. The particular equation is a cube root function with an offset. L* = 116(Y/Yn)^(1/3) - 16.

Yn is the Y value for a perfect white under the given viewing conditions. I hope this helps.   (Back to top)

I am a massage therapist. After a massage a customer said that when I had massaged her on a certain part of her body she could see a certain color, for ex. red, & at another spot she saw the color blue. Is there a reason to this? (817)
There are two possible reasons that I can think of. One is something called a pressure phosphene. They usually happen when you gently touch the side of your eye and you can see some colors. It is possible that the massage in different areas cause differing pressure on the eyes (depending on the position your client was in). A second possibility is a phenomenon called synesthesia. This is when stimulation of one sense produces a response in another sense. For example massage in certain areas might produce the red impression along with a feeling of slight pain (as a random example) while the massage in another area might have produced a blue sensation along with a soothing feeling (another random example).   (Back to top)

How do you find a RAL equivalent of an NCS colour reference? (816)
The RAL system is proprietary, so it is not easily possible to convert to/from RAL from/to any other system. That is even true with one that has been published, like NCS. The best I can recommend is to purchase the RAL swatches and visually match to the desired NCS color (you could also do the matching instrumentally).   (Back to top)

Why can't humans see ultraviolet or infrared energy? (815)
There are a few reasons for the range of wavelengths that we can see. One is that much of the interesting interactions between energy and objects happen in those wavelengths, so there is a lot of information for us to see there. There are also more "practical" reasons. UV energy is often damaging to biological tissue, so it would be potentially dangerous for our visual systems to absorb that energy. Some insect respond to UV energy, but they don't live nearly as long as us, so maybe the potential damage is not so much an issue for them. At the other end of the spectrum it becomes difficult for biological photoreceptors to respond reliably. Basically, because of the temperature of our bodies, receptors that could respond to IR would also be very noisy (IR cameras are often cooled for this reason) and it would be difficult for us to differentiate noise produced by our visual system from objects out there in the world.   (Back to top)

What color is chroma key paint for green screen back drops? (814)
Green! Seriously, it can be just about any color that stands out from the foreground objects or people. A high-chroma green is most commonly used, but sometimes other hues are selected. The camera/processing system is set up in the studio to use the selected color as the region to substitute in other video content. Here is a link to one source of green and blue chroma-key paint.   (Back to top)

Is it possible to determine the ink densities (or transmissivities) in a small area (~20 mm^2) of a four color image (CMYK) from its reflectance spectrum? The relative areas of coverage and overprint of the inks are not known. Illuminant and substrate spectra are available. (813)
Yes it is possible. However, in addition to the information you mentioned, you would also need to know the characteristics of the inks and their interaction with the substrate. Essentially, you need to have a model of the printing system and you could use that to determine the CMYK coverages needed to produce any given color. It is not a simple matter, but it is possible.   (Back to top)

How would I measure the yellowness of the sclera (whites) of the eye? Also, what instrument would be an appropriate measure haziness of the cornea? (812)
The best instrument would probably be a spot spectroradiometer (also sometimes called a telespectroradiometer). You point it at the object of interest like a you would a camera and measure the indicated spot. This would allow you to choose the appropriate spot on the sclera (or cornea) to measure. With controlled lighting, or a reference white measured next to the eye, you could get quite reliable measurements.   (Back to top)

What is the color temperature that makes the road most clear during driving, even under unconditional weather? (811)
I am not familiar with any research on this topic, but some might exist. My understanding is that moderate color temperatures (say around 4000K) are being used as a trade-off between the traditional halogen lamps that are too yellow to render colors well and the bluer discharge lamps that tend to produce a lot of visual glare for oncoming traffic. That might well be the best compromise.   (Back to top)

How do I match the actual fabric color in PhotoshopTM? Images are digitally shot, and the final output is four color offset printing. (810)
This is not a simple matter, but it can be accomplished with carefully calibrated and characterized imaging systems (camera, display, printer, and software). This is the domain of color management and I would suggest you look further into that area to learn more about it. "Real World Color Management" by Fraser et al. is one book that provides a useful introduction.   (Back to top)

What is the theoretical principals of the color change test in chemistry? (809)
How Stuff Works provides a great explanation and experiment.   (Back to top)

I am interested to convert a hex html or decimal RGB value to CIE 1931. How can I do this? (808)
You might try this site easyrgb.com   (Back to top)

Is 0.05ppm a suitable tolerance for measuring absorption on a spectrometer for beverages? At what concentration is the difference not perceptible? (807)
This would depend on what color the beverages are and what you are measuring. The only way to evaluate visual tolerances is with colorimetry, PPM on spectral absorptance functions tells you very little (perhaps nothing) about visual perception.   (Back to top)

What would an acceptable max display luminance setting be for a display that does not see direct sunight or much ambient light so that colors and text are easily readable? (806)
There is no set, agreed upon, answer. However it certainly is possible to make displays that are uncomfortably bright in dim surroundings. The useful maximum is probably somewhere between 500 and 1000 candelas per square meter.   (Back to top)

What is the unit of the viewing angle? Is it degree, radian or steradian? (805)
"Degree" is the unit typically used. However degrees and radians are interchangeable (like yards and meters they measure the same thing). Steradians, on the other hand, are used to measure solid angles like cones and are not appropriate for viewing angles.   (Back to top)

Using the color bar on Powerpoint 2003 I drag the brightness bar on the Device RBG mode, I get a darker color of apparently the exact hue. Is the hue is truly staying the same? Also, if I drag from R 200, to R150 to R50, is it decreasing in the amount of red equally in each interval? (804)
No, hue is not staying the same. Display devices are not linear, so that causes one problem, and even if they were, constant ratios of linear RGB wouldn't necessarily appear the same hue since the human visual system is nonlinear (although they would be closer). The only colors for which this will be approximately true are when you have only one non-zero RGB (i.e., just red, just blue, or just green being adjusted). On the second point, equal RGB intervals are not equal intervals in either amount of light (luminance) or perceived amount (brightness).   (Back to top)

"The Desktop Color Handbook" mentions using a "light source color rendering card" which has patches that look the same under light of the appropriate CCT, but different under other lights. Do you know who makes such cards, or how one could create one? (803)
I have seen such cards, but I don't know of any current manufacturer. "color rendering" really isn't the correct name. These cards are based on a pair of metameric samples that will match each other under the appropriate lighting. They are produced by having the samples prepared with differing spectral reflectance functions, but designed to match under a certain light. For example, gray metameric pairs designed to match under a chosen light could be made on a CMYK printer by printing one sample with black ink only and the other with a combination of cyan, magenta, and yellow (but no black).   (Back to top)

I am a Color Technician for a woman's retailer which specializes in black, white, and neutral only clothing. We test our associates with the Munsell 100 Hue test. Is there a similar test to evaluate for neutrals only? (802)
There appear to have been some developed. If you do a search on "lightness discrimination test" you can find some references. However, I am not aware of a commercially available test similar to the Farnsworth-Munsell test. It wouldn't be difficult to create one of your own. You would just need to make a set of gray samples closely spaced in lightness (perhaps 100 or so from white to black) and then ask people to put them in order. You could score it in the same way as the normal Farnsworth-Munsell test.   (Back to top)

How can I convert RGB or CMYK shade to Pantone? (801)
Pantone is a proprietary system, so unless you license their software (or buy software from someone who has licensed their conversions), you cannot make this conversion. In addition without accurate display or printer characterization, the RGB or CMYK values would be inaccurate.   (Back to top)

Is there an accepted universal standard for the calibration of color Spectrophotometer? Are there white standards available with certified reflectance values? (800)
The universal standard is the theoretical perfect reflecting diffuser (PRD). A PRD is a perfect reflector (reflects 100% of the incident light) and a perfect Lambertian diffuser. No such material actually exists, but pressed PTFE (sometimes called Halon) is a good approximation. Materials are calibrated by national standardizing laboratories to provide reflectance factor data relative to the PRD for a given illumination and viewing geometry. In the USA the national laboratory is NIST. Other examples are NPL in the UK, and NRCC in Canada.   (Back to top)

Are there maximum/minimum values for a* and b* like the min and max for L*? (799)
No, there are not specific limits. The limits for given types of materials (or lights) would depend on both their material properties and the viewing conditions. You might look at the MacAdam Limits to see what some theoretical limits for reflecting objects look like. The a*b* limits depend on the hue and lightness of the object. In imaging applications, limits for 8-bit encoding are often set as the range from -127 to +128 in both a* and b*. This is adequate to cover the gamut of most systems.   (Back to top)

Is color a quality in physics? (798)
The main definition of color is that it is an attribute of the human perception of light. It is not a property of physics (although physics can be used to describe the light stimulus), but a property of human perception. So, according to that definition, the answer is a very definite "no". However the word color is unfortunately sometimes used with other definitions. For example the term "color" is used in physics to describe a property of the theoretical subatomic particles known as quarks. In that sense of the word, "color" would be a quality of physics.   (Back to top)

I have noticed a couple of different species of early-flowering trees have pink blossoms which turn white literally overnight. It is the speed of the process which is intriguing. Do you know how it works? (797)
I don't know the mechanisms for sure, but it could be that the pink colorants are very light sensitive and fade shortly after the flowers bloom. Also, it could be that they are transported quickly to different parts of the flower or spread across the petals as the petals grow (thus diluting the color from pink to more of a white). Plants grow incredibly quickly this time of year.   (Back to top)

Do you know where I can purchase Hess Ives Color standards, both physical standards and papers publications? (796)
I'm afraid I don't know of a source, but I would suggest contacting Tintometer since they make instruments capable of measuring Hess-Ives units.   (Back to top)

How can tulips be so many different colors when they are the same plant? (795)
It is for the same reason that people look different from one another. Part of our appearance (and that of a tulip) is genetically programmed and another part is due to environmental factors. The genetic code of the tulip has the information necessary to produce the chemical colorants in the petals of the flower (or lack thereof) allowing different tulips to express different colors. Humans have spent many years selecting tulips for color and other features to assure that certain tulips have the desired genes. In humans, things like eye color, skin color, etc. are encoded in the genes we inherit from our parents.   (Back to top)

Is there such an instrument as a hand-held spectrometer for measuring the color temperature of light sources? If so, how much do they cost? (794)
Yes, there are handheld colorimeters from companies like KonicaMinolta that are capable of such measurements. They range in price from several hundred to several thousand dollars. At the higher end, there are portable spectroradiometers from companies like PhotoResearch that are in the tens of thousands of dollars range, but also provide spectral radiance data in addition to color temperature.   (Back to top)

Densitometers can be purchased with or without polarizing filters. Why are both types used? Which type provides the best correlation to perception? (793)
The polarizing filters help eliminate gloss in the measurement. This means less light is being measured and therefore density is higher. This measurement is used sometimes to allow the measurement of wet inks that are still glossier than the finished product, or to compare surfaces with different gloss characteristics. Observers tend to move the samples to minimize gloss when judging color.   (Back to top)

How do you convert ΔL ΔC ΔH values for colour differences in CIELCh to the equivalent ΔL Δa Δb colour difference values in CIELab, when you do not have access to the absolute values for the original measurements? (792)
Unfortunately, you can not.   (Back to top)

Are there some basic averages for the LRV of human skin? (791)
I don't know of any specific data and there would be quite a range, but an old photographers trick is to use the back of their hand to measure the light level if they don't have a standard gray card with them. This is equivalent to assuming that the skin has a reflectance of about 20% and that might well be a reasonable assumption on average.   (Back to top)

At what age do children develop good color perception? (790)
The visual system of infants is still developing after birth. It is difficult to say exactly how long it takes color vision to become "normal", but by about 6 months of age the visual system is essentially the same as an adult. More significant, probably, is that visual acuity improves rapidly during those first six months and stimulation of all types from the visual world does aid in this early development. Here is a link to a good page on infant vision.   (Back to top)

Can you define what is Multiflux math model used in color mathing? (789)
Here are a couple of suggested references from our faculty:

  • H. G. Völz, Industrial Color Testing: Fundamentals and Techniques, 2nd ed, Wiley-VCH, New York, 2001.
  • Articles by Willard Richards
   (Back to top)

I have used three online color space conversion calculators and I get three different sets of numbers when I convert from XYZ to RGB. What's happening? Who's right? (788)
It is quite likely that they are all accurate, however they all might be using slightly different definitions of RGB or assumptions on how the XYZ values were obtained. This is one problem with RGB; it is not specifically defined and is device dependent. It is probably best to just choose one converter and stick with it.   (Back to top)

Can light be a "Brown" color? If not, why not? (787)
This is one of my favorite questions. The short answer is "no". Brown cannot be perceived as a light source because it is only perceived as a related color that is "dark" and "low in chroma". This can only occur for colors that are less luminous than the white we are adapting to. Here is some more detail from one of my other websites.

Q: What is brown?
A: Brown is dark, low-chroma (desaturated), orange. In other words, an orange light that is perceived in an environment that makes it look dark and less saturated will appear brown. A brighter surround is such an environment. Brown is a special sort of color perception that requires this relationship to its environment in order to be perceived. That's why you can't go to a hardware store and buy a brown light bulb!"   (Back to top)

What is the RAL number for PMS 268 plum? I've attempted to find a cross-reference tool and have not been successful! (786)
Both RAL and Pantone PMS systems are proprietary. They make their money on selling the samples that embody their systems (or software to do conversions like you are looking for). They are both protective of their systems in order to retain their market. That is why you cannot find a conversion tool and also why I can't help you.   (Back to top)

When purchasing an encapsulated Haz-mat suit, Level A, what colors have the best visibility for the different environments in which they might be used, i.e, sandstorms, snow, heavy rain, thick smoke, etc.? (785)
The best color for each situation will be different. The thing to keep in mind is that the visual system functions on contrast, the differences between colors of objects. For example in a snowstorm with snow on the ground, black would be by far the best color (most contrast with white), even at night. In thick smoke or heavy rain at night, black would probably be the absolute worst color. White would be the best then with respect to contrast. However a secondary consideration is that you want them to stand out from other common objects. In that case, you would want a very light color that is rare (like blaze orange or fluorescent yellow-green).   (Back to top)

Roughly how large is the overall remaining perceptual non-uniformity of color tolerances in CIELab space, when using the ΔE94 and ΔE2000 color distance formulas? (as compared to the 6:1 non-uniformity of simple ΔE*ab)? (784)
It is a serious estimate, but if you are assuming 6:1 in CIELAB ΔE*ab, I would say that it would be about 3:1 or 2:1 in either ΔE94 or ΔE2000. Whether or not ΔE2000 is a significant improvement over ΔE94 is questionable. Both are significant improvements over ΔE*ab.   (Back to top)

How can I have someone create a paint for me using a theoretical spectral reflectance curve? (783)
There are computer color matching systems that are capable of determining the best spectral match possible for a given paint medium and colorants. In any given paint system, there are limitations, but many spectra can be matched. The best advice is to find a manufacturer of the type of paint in which you are interested and send them the spectrum. They should be able to compute the best match they could make for you.

Hardware and paint stores have color matching systems that can be used to measure a sample and formulate a match. However, it is likely that such systems are aiming for color matches, which are not always spectral matches. That would be an easy way to get something close if you have a sample of what you are interested in producing.   (Back to top)

How does chameleon paint (i.e. paint which color depends on viewing angle) work? What is its composition? (782)
Such "effects pigments" work on the basis of interference in the layers of material that are dispersed in the paint. This is the same effect that causes soap or oil films to exhibit a range of colors. The wavelength of constructive interference varies with the angle of illumination and view and that results in the range of colors we see. This website provides a nice overview. You might also search for terms like "interference pigment" or "pearlescent pigment" to learn more.   (Back to top)

How do I calculate the dominant wavelength of a color sample with X,Y,Z or x,y? I do not want to draw it in the colorspace. (781)
I am not aware of any code to do this directly. You would have to do the computation in terms of xy. The task would be to define the line that connects the sample xy with the white point xy and then solve for the intercept with the spectrum locus (which is defined by the color matching functions and not analytically). It would have to be some form of numerical solution. There is also some information and suggestions from visionscience.com.   (Back to top)

Why does your hair change color during the season? (780)
I found this nice answer on the MadSci Network.   (Back to top)

How to convert CIELAB data to Yellowness and Whiteness index? (779)
The equations are available in most textbooks on colorimetry, such as Berns'"Principles of Color Technology, 3rd Ed.". You will have to first convert the CIELAB coordinates back to CIE XYZ values and then compute the yellowness and whiteness indices you are interested in (there are several) from there.   (Back to top)

Which minimizes solar heat absorption better, polished aluminium or white paint on it? (778)
It would depend on the specific materials, but in general a good polished aluminum will reflect more light than a typical white paint. The aluminum should be well above 90% reflectance while the paint will be between 80% and 90% reflectance. You also have some control over where the reflected energy goes with the mirrored surface whereas it is reflected diffusely in all directions from a white surface.   (Back to top)

How does the eye determine the various colors of visible light? (777)
Our perception of colors comes from a combination of the sensing of light in the eye and the processing of that information in the brain. The first step is that we have three types of cone receptors in the eye that respond to different wavelengths of light. Approximately, they respond to red, green, and blue light respectively. It is the responses of these three receptor types, in various proportions, to the light present in a scene that initiates the process of color vision.   (Back to top)

Could you please tell me, what color would 1.2Y 6/11 be? (776)
Since it is a Munsell designation, which is a published color system, I can. Munsell also has the advantage that you can estimate the color appearance directly from the notation. This color would be a slightly greenish yellow that is fairly light and very saturated. This link includes a nice explanation of the Munsell system.   (Back to top)

Why do black clothes appear blue in the artificial light of a clothing shop? Then when you take the item into natural light it is black? Why is that? (775)
There are many types of artificial light and the interactions of light with objects can have very significant effects on the perception of the object color. It all depends what the material is made of and how it is colored. However, you might be seeing a purely perceptual effect. If the lighting is yellowish (like incandescent lamps), then there is a visual contrast effect (technically called the Helson-Judd effect) that makes darker colored objects appear bluish. What is happening is that the in contrast to the overall yellowness of the scene, our visual system adapts and where there is little light (the dark objects) our we notice the perceptual opposite of yellow, which is blue. It is always best to judge colors of objects under the variety of lighting in which they will be used (or worn).   (Back to top)

What type of Pantone Guide shall we refer to & which instrument is suitable to measure the values of colour on aluminum foil with a flexo printing process? Since Aluminum has glossy as well as the matt finish then is there any need to change the settings of the instrument? (774)
I can't help you with the Pantone guide; I'd recommend contacting Pantone on that one.

On the measurement geometry, that is difficult with a metallic substrate. I suspect you are interested in the color of both the diffuse reflection and the specular reflection (especially if your ink is transparent). You really do need to make two measurements to evaluate both. I would suggest that you might use a traditional 45/0 geometry to evaluate the diffuse reflectance and a diffuse/0 (specular included) measurement to include the specular reflectance. It might also be insightful to look at the differences between the two measurements. As an alternative, you could use the specular included and specular excluded measurements on a single integrating-sphere instrument and compare those.   (Back to top)

We print on Aluminum foil with a flexo process. What type of Pantone Guide shall we refer to & which instrument is suitable to measure the values of colour? Since Aluminum has glossy as well as the matt finish then is there any need to change the settings of the instrument? (773)
I can't help you with the Pantone guide; I'd recommend contacting Pantone on that one.

On the measurement geometry, that is difficult with a metallic substrate. I suspect you are interested in the color of both the diffuse reflection and the specular reflection (especially if your ink is transparent). You really do need to make two measurements to evaluate both. I would suggest that you might use a traditional 45/0 geometry to evaluate the diffuse reflectance and a diffuse/0 (specular included) measurement to include the specular reflectance. It might also be insightful to look at the differences between the two measurements. As an alternative, you could use the specular included and specular excluded measurements on a single integrating-sphere instrument and compare those.   (Back to top)

How do I convert from spectral reflectance (from a hyperspectral imager) to CIELAB colorspace? (772)
You integrate the product of the reflectance, a selected illuminant, and the CIE color matching functions with proper normalization to obtain CIE XYZ tristimulus values. These values are then used in the computation of CIELAB coordinates. A colorimetry text such as Berns' "Principles of Color Technology, 3rd Ed." explains this procedure in detail.   (Back to top)

Can a consumer grade flat bed scanner be used as a colorimeter? (771)
The general answer is no, but you can make a reasonable approximation if you know the characteristics of the material you are scanning. For example, if you are always scanning photographic prints that are made of the same three dyes, then it is possible to derive an accurate conversion from the scanner readings to XYZ values for that material. However, when you scan other materials, the conversion would not be accurate.   (Back to top)

The lighting goal for our new indoor shooting range is to have 100 footcandles of light on each target. Our question is this: should the walls and ceiling around the target be light in color or dark in color? (770)
I would make them light in color since this will increase the perceived contrast of the targets themselves and make them essentially more visible. Although with the intense focus on the target that usually accompanies shooting, the effect might be very small.   (Back to top)

Can you suggest an ideal color scale for a digital elevation map to be printed in a scientific paper? Is it possible to have a color scale that looks good in color and in black and white? (769)
I'd suggest you check out the information at colorbrewer.org. It is based on good perceptual studies and should help with your needs. What you need is a scale that is monotonic in luminance/lightness so that the information is preserved in black and white images.   (Back to top)

Suppose I introduce the same amount of noise in individual channels of a YUV image of 420 format (chroma has been downsampled). Which image is the most noticeable, the one with noisy Y, U, or V? (768)
Noise in the Y dimension will be most noticeable. However, YUV is often poorly defined and the differences in noise perception are often not as large as expected since there is luminance information in the U and V channels.   (Back to top)

Can you point me to the actual formula the Photoshop Hue/Sat tool is using to change given colors in an image?Can you point me to the actual formula the Photoshop (tm) Hue/Sat tool is using to change given colors in an image? (767)
Sorry, I can't. The inner workings of programs like Photoshop are usually kept proprietary and it is not always obvious at all what these controls do.   (Back to top)

What are the colors of a complete spectrum? (Starting with the color with the longest wavelength.) (766)
The classic answer is ROYGBIV. That's shorthand for red, orange, yellow, green, blue, indigo, and violet. However, it really isn't that simple. When humans view the spectrum, they don't see just 7 discrete hues, but rather a continuous range of hues from red through violet. The number of distinct hues we can see would depend strongly on the specific viewing conditions, but it is safe to say that it could be well over 100! When naming colors, we tend to group them into categories of similar colors and that is why the ROYGBIV shorthand is so popular.   (Back to top)

What color measurement system would be best to define colors for a liquid, to be described in a US patent? (765)
First, you would have to measure the spectral transmittance of a sample and define the measurement conditions such as the path length through the liquid that you are measuring. You could then do normal colorimetric computations with the measured spectral transmittance. You would have to select and appropriate illuminant and observer and then you could compute CIE XYZ and/or CIELAB coordinates to define the color.   (Back to top)

Why is blue ink most commonly used for writing? (764)
As with many historical questions, there are probably many factors involved. This website gives some history on ink and suggests that blue ink was the first color developed after black. That probably goes a long way toward explaining its popularity. Also, the utility of ink is in its legibility (in most applications) and legibility comes from contrast. After black, blue would provide the most visual contrast on white (and light) papers and thus be the easiest of the non-black colors to read. Beyond that, blue has also traditionally been one of the most popular "favorite" colors. It is likely that all these factors, and more, combined to make blue ink popular for writing.   (Back to top)

What is the difference between the L*a*b* values and the L a b values when using a Minolta colorimeter? (763)
L*a*b* refers to CIELAB coordinates that are commonly used as the basis for color difference measurements. Lab refers to an older color space known as HunterLab. It was a predecessor of the CIELAB space and, unless someone specifically asks for HunterLab values, it shouldn't be used. The values are not equivalent.   (Back to top)

Do you do research on ink jet printer color consistency? We are interested in printing solid colors for visual evaluations. We have a high-end ink jet and use photo paper, but we see color differences of up to 0.5 Units ΔE* between prints using the same printer, inks, profile and paper. (762)
We do some research on related topics. Given the variability in papers, inks, and the printing process, I would be very surprised to see performance better than what you are quoting. In fact, I would suspect it is difficult to print the same color on two edges of a piece of paper within a tolerance of 0.5 ΔE*. You should be very happy with the performance you are seeing.   (Back to top)

My spectrodensitometer states its measuring geometry is 0/45, and its standard observers are 2 and 10. Are these angles related? Which should I use? (761)
0/45 refers to the geometry of illuminating the sample (0 degrees from the normal, or perpendicular) and detecting the reflected light (45 degrees from the normal). That is unrelated to the two and ten degree observers. Those refer to the field size when the original experiments were done to determine the standard observers for colorimetry. Think of them like have two different people look at the matches. Either observer would be appropriate for your application. It is best to be consistent, record which one you use, and use whatever is requested by your customers/suppliers or any standards you are following. More on all these topics can be found in books on colorimetry such as Berns' "Principles of Color Technology, 3rd Ed."   (Back to top)

Is there a way to determine what a symmetrical circle 1% dot, 120 line screen should measure? I am looking for a published table or a equation as I need to determine this on several different screen rulings. (760)
Well. that would depend on what you assume a 100% dot is. If you assume 100% means that the dots just touch when they are diagonal from one another (adjacent dots overlap), then you can take a right triangle with two sides equal to the dot spacing, compute the hypotenuse and divide that by two to get the radius of a 100% dot (skip the divide by two if you want diameter). Then dividing that by 100 will give you the radius of a 1% dot. Of course, this ignores any sort of irregularity in the dots and dot gain.   (Back to top)

I am working on a plastic matched automotive black (GM 848) where the color is visually darker, but it measures LIGHTER than the standard. Can you please explain why? (759)
It's difficult to say without seeing the samples, but two possibilities come to mind. One is simply that there is some sort of problem with the measurements or the instrument. Assuming that is not the case (e.g., both samples measured at the same time, on the same instrument, in the same way), then I would suspect that there is a difference in the surface characteristics of the two samples. For example, the one that looks darker might have more of a glossy (or less matte) surface than the one that looks lighter. Depending on the instrument geometry you use, this difference might not show up in the measurements. If you take a glossy and matte surface that measure the same for total reflectance (0/d), the matte surface will usually look lighter. If you measure the two on a 0/45 instrument, the reading for the matte surface will be higher, more in line with the visual assessment.   (Back to top)

What is the mathematical equation to convert Lab or XYZ to Density? (758)
I'm sorry, there isn't a direct conversion from CIELAB or XYZ to density. CIELAB and XYZ are based on visual color responses, while densitometers are designed to measure material properties (ink or dye amounts) of various systems.   (Back to top)

I sometimes catnap at my computer or while reading and when I wake everything looks green tinged for about 20 seconds. Why? (757)
This can be explained by chromatic adaptation. If you close your eye and look toward a light source you will notice that you can perceive some red light passing through your eyelids. When your eyes are exposed to this red light for a while (while you nap), they become relatively less sensitive to red light and therefore relatively more sensitive to green light. When you open your eyes, they are exposed to the world of fairly neutral light, but since your eyes are more sensitive to green light, everything appears to have a tinge of green for 20 seconds or so. This is the same effect as chromatic afterimages that cause you to see one color after staring at another for a while.   (Back to top)

Does the color of a laser affect the velocity of the light wave projected by the laser? (756)
In a vacuum, the answer is "no". The speed of light is the same for all wavelengths (laser colors). In other materials, the speed of light does become a function of wavelength which is why we have dispersion and prisms can separate white light into a spectrum. The change would depend on the material and is defined by the material's index of refraction and how that index varies with wavelength. The index of refraction of air is essentially identical to that of a vacuum for visible wavelengths, so for all practical purposes the answer in air is also "no".   (Back to top)

What is the physics behind a blue-yellow polarizer such as the Singh-Ray Gold-N-Blue filter which photographers use to add yellow or blue highlights to polarized parts of a scene? (755)
I am not very familiar with those particular filters and I couldn't find any details on them. However, it sounds like you are halfway there and what you need is a second polarizer on the other side of the cellophane. When you rotate one of the polarizers, you will get a range of colors coming through the whole sandwich and it will work in either direction. Here is a little experiment from the Exploratorium that does something similar.   (Back to top)

Is is possible to convert R, G, B values of an image captured using a flatbed scanner to densities? I can convert R, G, B to CIELab using the ICC profile of the scanner. Is there a way to convert CIELab to Densities? (754)
Since the spectral sensitivities of your scanner most likely differ from those for a given density standard, it is very unlikely you would be able to directly compute densities from the RGB measurements. The best you could do would be to construct a lookup table that would be appropriate for a given type of input medium (much like the ICC profile you mentioned). The same goes for a CIELAB to density conversion. It would be medium dependent since the two are derived with different spectral responses.   (Back to top)

Where could an art reproduction facility obtain an optical device that used spectral-based imaging? (753)
There isn't a commercial implementation as yet. Several companies are considering such a device including Sinar and Geospatial Systems. At this point, you would need to implement this on your own. See the Art-SI page for details.   (Back to top)

We know density is derived from the transmitted spectral power distribution. Can you suggest a reference that provides the responsivity functions for Status A and Status M densities, as well as the specific function for the calculation of density? Also, what is the proper illuminant to use? (752)
The standard procedures for computing density are published by ISO (ISO 5 Photography - Density Measurements). It appears that part 3 (ISO 5-3) includes the spectral details. The procedures and data are also described in Hunt's book, "The Reproduction of Colour, 6th Ed." in chapter 14.   (Back to top)

What is "camera gamma" and its relationship to NTSC/HDTV video? (751)
Gamma is the nonlinear relationship between the light intensity in the scene and the encoded camera responses that is normally described with a power function. The exponent of that power function is called "gamma". In video, the camera signal is encoded in this nonlinear way to compensate for a similar nonlinear relationship between video signal and display intensity in traditional CRT displays. However the compensation is rarely complete since it is often desired to increase the physical contrast of the video images. Hunt's text, "The Reproduction of Colour" provides much more background on this topic and Poynton's FAQ provides many answers on the confusing use of the term "gamma'.   (Back to top)

How does coloured text affect accommodation? (750)
There are two ways that the color of text impacts accommodation. The first is simply through luminance contrast. Text that has more luminance (or lightness) contrast is easier for us to focus on. For example black on white has far more contrast than yellow on white (or blue on black). Secondly, there is chromatic aberration in the eye, so if we are focused on text of one color, it is quite possible that text of another color will be out of focus and require us to accommodate again to read it.   (Back to top)

How can I meaure the color of clear solutions? We want an objective measurement (wavelength) of colors of various juices and wines. (749)
You would want to use a spectrophotometer or colorimeter capable of transmittance measurements using cells that can hold the liquids. There are a number of manufacturers of such instruments. Two that are well-known for these types of measurements are Hunterlab and Tintometer.   (Back to top)

When choosing an umbrella, what color is best to protect yourself from UV light? (748)
Technically it's UV radiation, not UV light, since the term "light" is only used for visible wavelengths. There is not a direct correlation between color and UV absorption/reflection so there is no simple answer to your question. I would suggest you stick with an umbrella that allows no, or very little, light to pass through (e.g., you can't see the sun looking through it) and it will also be very likely to stop the UV energy as well.   (Back to top)

I am teaching color theory to our press operators and I am wondering if there is a full color spherical L*a*b model illustration that I can download, and if necessary purchase. (747)
If you do a google image search on "CIELAB", you will find a collection of images. I will leave it up to you to determine which have copyright restrictions.   (Back to top)

I would like to know if the color of the water (by adding food color dyes) will affect the absorption rate of water and thus the color of the white flower over time. (746)
There is no reason to think that the color of the water will change the rate of uptake by the flower. However, the color imparted will appear different for different colors of dye. Some simply make more visible changes than others. It will also depend on the amount of dye that you put in the water and this is a difficult thing to equalize across different colors. What you are seeing is the different strength of the dyes to produce a visibly noticeable effect. There are many websites with experiments on coloring flowers this way (carnations are a common choice), for example KidZone.com.   (Back to top)

What is the Kubelka Munk Theory? What its use in textile dyeing process? Would you please provide me any literature on the Kubelka Munk theory? (745)
Kubelka-Munk theory represents a series of mathematical models that can be used to predict the spectral reflectance properties of materials from measured absorption and scattering characteristics of the medium and colorants. Predicting color matches in the textile industry is one application of the theory. Much has been published on Kubelka-Munk theory and computer colorant formulation (or color formulation). A good starting point is an introductory textbook on colorimetry such as Berns' "Principles of Color Technology, 3rd Ed.".   (Back to top)

Is there an existing paint industry standard system for expressing (and thus potentially matching) all the visual characteristics of a metallic or metallic flake paint, whether one-coat or two-coat (colored transparent over metallic or flake)? (744)
I am not sure if there are any industry standard procedures for these measurement and matching procedures. I would recommend checking with ASTM for the existence of such standards. However, there are commercial multi-angle instruments available for characterizing these materials. One example is the the X-Rite MA-68. You might contact X-rite to learn more about that instrument and any related standards and applications.   (Back to top)

I am trying to calculate the colour of a coating. I have a graph of wavelenth versus reflectivity. Is there a simple way to convert this graph into RGB values or some similar standard? (743)
Unfortunately this is not quite so simple. RGB values are not standardized, so their meaning as a color specification is dubious at best. There are fairly straightforward colorimetric calculations that are performed to specify color matches (CIE XYZ) and color appearance (CIELAB) from spectral reflectance measurements. These might be helpful in your application. I would recommend a good introductory text on Colorimetry (such as Berns' "Principles of Color Technology, 3rd Ed.") to learn more about the details of these computations.   (Back to top)

Since a mirror reflects most of the light that falls on it, as does any white body, what is the difference between the two? (742)
This is a matter of geometry. A perfect mirror reflects all of the light that strikes it, but reflects it as regular, or specular, reflection. That means all the light is reflected at an angle equal to the angle of incidence and opposite the normal to the surface. A perfect white also reflects all the light incident on it, but reflects that light diffusely. In other words, the white scatters the incident light in all directions. That's why a white object looks white from all angles, but you can only see yourself in a mirror when you look at it directly (in line with the normal to it's surface).   (Back to top)

I know that the color of a body depends upon the color that it reflects. What causes some bodies to be transparent, others translucent still others to be opaque? (741)
There are many factors involved, but the main one is scattering of light. A material with no scattering can be transparent, one that scatters a little is translucent, and one that scatters a lot is likely to be opaque. And the amount of scattering depends on various material properties such as surface roughness, homogeneity of the material, changes of index of refraction within the material, etc. Also, another important factor is the amount of light absorbed. Something that doesn't scatter at all, but absorbs 100% of the incident light, will also be opaque.   (Back to top)

I found a source that says an RGB of 194, 32, 11 for Calder Red. Can you tell me what proportions of red, yellow, and blue paint should be mixed to get that RGB? (740)
Unfortunately not. Neither RGB, nor red-yellow-blue paint, are standardized specifications of color appearance. Both would have to be well calibrated and characterized to define a match. Your best bet is to find a sample of the color you are looking for and then experimentally mix the paint to make a visual match (or take the sample to a paint store for matching if you are interested in large amounts of paint).   (Back to top)

Where can I buy Baker-Miller pink paint? (739)
I don't know of any particular source for Baker-Miller pink paint or even a standard definition of what it is. Your best bet would be to find a sample of the color you want and then go to a paint store to have them custom match it for you. However, you might want to do some more research on the topic as well. The reason there is no standard color is probably because the effects of calming people are not consistent from person to person and the pink exposure has also been shown to enrage people if they are left in pink rooms too long. I think the effect is more folklore than well-understood science. There are certainly emotional effects of color, but they are not consistent from person to person. Faber Birren's book "Color and Human Response" is a good introduction to the topic. There is also this Color Matters page with a little more information on Baker-Miller pink.   (Back to top)

I want to make a slate grey color from white exterior latex paint. What additional colors and quantities of color will I need to mix? (738)
You would need to mix in some black paint (or more simply some black colorant). The amount would depend on just how dark you think "slate gray" is. You would probably need to do some experimenting. I would also recommend mixing all the paint together to get consistent color. Since that would be one big vat of paint, it might be easier for you to go to a paint store and ask them to make a match for you. They could add colorant to each gallon in a consistent manner and convert that paint from white to gray for you.   (Back to top)

This pertains to colors being used for home theater projection screens. Neutal grays have been suggested as the best color since they should not shift the color of the reflected image. Munsell grays are reported as neutral for illuminant C. What would the RGB value be for Munsell N8 and N9 under D65? One source lists N8 as 202 202 202 (L*ab- 81.3256 0.0044 -0.0087, Yxy as 59.0619 0.31272 0.32900). Is this correct? (737)
The Munsell neutral samples are quite nonselective, meaning they will remain neutral under a wide variety of illumination levels. Your numbers seem reasonable, but entirely too precise. As a good approximation, N8 will have L*a*b* values of 80, 0, 0 and N9 will have L*a*b* values 90, 0, 0. Conversion to RGB values will depend on the particular display characteristics and setup, but your values of 202,202,202 are not unreasonable. You might want to adjust them all up or down slightly if you would like a bit lighter or darker background.   (Back to top)

I am an artist interested in painting with photochromic inks or paints. Do you know of a supplier? (736)
I don't know of any specific vendors, but a search seems to suggest that some are available. See this Google search.   (Back to top)

We have two items painted with Munsell N7 which are significantly different in shade. Is this normal? How can I measure if the differences are within specification? (735)
It is not unusual for materials that are supposed to have the same color to have perceptibly noticeable differences. Whether or not they are within specification depends on the tolerances set for a particular application. Such tolerances are normally established by setting acceptable lightness, chroma, and hue ranges in a color space such as CIELAB and using spectrophotometry to measure the samples. Alternatively, tolerances are sometimes setup visually. You could select the darkest and lightest samples that are acceptable to define the range that you would accept in your application.   (Back to top)

I am building a pit solar greenhouse and need to decide what color to paint the non-glazed walls. White would be the best for reflection onto the plants but I am also looking for more pleasing colors. What is the best color for growing plants? (734)
Most plants are green, which means they are reflecting more green light than other wavelengths. Those other wavelengths are being absorbed by the plant to help them produce energy. Taking away the green light (which the plants don't use as much) leaves you with purple. So while you are correct that white would result in the most light getting to the plants, as a second choice I would go with a light purple.   (Back to top)

Why isn't E point (x=0.3333 - y=0.3333) used as a standard illuminant for color matching and ΔE? (733)
It is used on occasion, but since it represents a purely theoretical illuminant (equal energy at each wavelength) it never occurs in a natural viewing environment. Therefore many prefer to use something like an average daylight distribution (such as Illuminant D65).   (Back to top)

I am working on honeybee color vision. Using a honeybee specific color diagram, we know how to calculate dominant wavelength. How do I calculate the dominant wavelength of a color sample which resides in my color diagram in the "magenta" (or purple) zone. (732)
The way it is done in normal colorimetry is to draw a line from the color through the white point to the spectrum locus (rather than the other way) and then the wavelength of intersection is called a "complementary wavelength" or "complementary dominant wavelength". Thus you will end up with "green" complementary wavelengths for those "magenta" colors.   (Back to top)

Why are the colors of Christmas typically red and green? (731)
There are various stories and theories, but this explanation seems to capture the essence of several of them.   (Back to top)

I work for an automotive finishing company and use an X-rite MA68II for measuring color. Which should I use, L*a*b*, or L*C*h°? Everyone seems to use L*a*b*, but I'm not sure why. (730)
The two represent different ways to represent the same CIELAB coordinates. L*a*b* are the rectangular coordinates and L*C*h are the cylindrical coordinates of the same space. So, in a sense, it doesn't matter which you use. L* is the same in both cases and correlates with our perception of lightness. Some people feel that L*C*h is more intuitive for describing colors and tolerances (C* representing chroma, and h representing hue) and choose to work in those coordinates. However, at times it is simpler to work in the rectangular coordinates where a* represents redness-greenness and b* represents yellowness-blueness. It really is a personal preference based on the application and user's experience, but normally L*C*h are a little bit more intuitive and effective (especially for tolerances).   (Back to top)

How long does it take for your brain to recognize color? (729)
This is not an easy question to answer since it will depend on many variables including the way the color is presented and the response required from the observer. For example, you might be able to recognize a color (or color change) in a very short pulse of light, but it could take you significantly longer to produce the word required to describe the color. Unfortunately there is no simple answer for this question. However, if you type the words "color", "reaction," and "time" into google, you will find lots of resources that describe and demonstrate various experiments that might be helpful.   (Back to top)

Can you provide a mathematical formula to convert a RGB color value in CMYK color value? (728)
Unfortunately there is no single simple conversion formula to go from RGB to CMYK. It depends on the particulars of the devices and their primaries. If you do a search on "RGB to CMYK Conversion" on the internet, you will find a number of resources explaining the procedures. Here is just one example that might get you started.   (Back to top)

How do mood rings work? (727)
They are liquid crystals that change color with temperature. A nice explanation can be found at owstuffworks.com .   (Back to top)

At what illuminant temperature are Munsell neutrals (N6, N7, etc.) designed to be neutral? (726)
The Munsell samples are specifically designed to be viewed under CIE illuminant C (simulated daylight with a correlated color temperature of about 6774K). However the actually samples are quite spectrally nonselective (i.e., flat spectral reflectance curves) and should appear neutral under a variety of white light sources.   (Back to top)

Obviously having a single colour on two different stimuli (each encompassing a different meaning) on a workstation will cause confusion. What are these problems from a psychological, cognitive, or ergonomic perspective? (725)
I received the following suggestions from a colleague far more knowledgeable than me in this area....

Here's a relevant article: Smallman, H. S. & Boynton, R. M., Segregation of basic colors in an information display, J. Opt. Soc. Am. A, Vol. 7, No. 10, 1990.

This site is also very helpful: colorusage.arc.nasa.gov

Also of interest: colorbrewer.org

There is also a book by Colin Ware called Information Visualization: Perception for Design that is supposed to be quite good.   (Back to top)

Are the colors that we see during the day, present at night - only we cannot see them? Or are the colors that we see during the day not present, or altered, because of the low light? (724)
The physical stimulus for color is still there, it's just that the amount of light is reduced to the point that we can no longer perceive color. For example, if a photograph is taken with long enough exposure time the colors will look just like a daytime photograph. So in terms of your question the "colors" are still there, we just cannot see them.   (Back to top)

What are the names of pigment suppliers who mfg or distribute metameric pigments? (723)
They all do! Metamerism is not a property of individual pigments, but a property of pairs of color samples (they match under certain viewing conditions despite spectral differences). You can make them out of all sorts of colorants.   (Back to top)

What are the evolutionary advantages and disadvantages of impaired color vision? (722)
It is thought that normal trichromatic color vision provides advantages for finding healthy food and healthy mates, both of which are selective advantages for evolution. However, it is clear that people with color vision deficiencies can function quite well in the world and therefore there hasn't been enough of a disadvantage of these deficiencies to make them fade away through evolution. There are even reports of some situations in which color deficient observers can see patterns that are masked by all the color variation that normal observers might see.   (Back to top)

I am developing paint color regulations to help buildings constructed on mountainsides blend into their surroundings to minimize their visual impact. What maximum LRV do you recommend for an environment typically consisting of darker browns, grays, and greens as the "base" colors in order to keep buildings from "standing out"? What would be the most appropriate instrument for measuring the LRVs of paint/stain for enforcement purposes? (721)
You would want the paint LRV to be similar to that of the background environment. In general this is taken to be about 20% for natural scenes. I would use that as a guideline and perhaps allow slightly higher values as well. Perceptually, a 20% reflectance appears to be midway between white and black, so this is a reasonable number. There are a variety of instruments that could perform this measurement, but a handheld spectrophotometer would be the most accurate, flexible, and easy to use choice.   (Back to top)

How does the color of a room affect people's moods? (720)
Emotional responses to color can be very real, but they do vary in type and magnitude from person to person. Many times these responses are from learned associations. Faber Birren's book, "Color and Human Response" is a good source of well-grounded information on this topic.   (Back to top)

What are the equations for McAdams ellipses? Are they location dependent in the 1931 chromiticity diagram? (719)
There are no equations for MacAdam's ellipses. They represent data on the variability of color matches for an observer when matching lights of various chromaticities and yes, they are location dependent in the 1931 xy diagram. I would suggest reading about this type of work in Wyszecki and Stiles' reference book "Color Science" and then exploring the original MacAdam papers on the topic if you need further details.   (Back to top)

It makes sense that I should want window glass with the highest Color Rendering Index available in the performance category that I need; but how do I judge the relative CRI when all options are between 87 and 95? (718)
Color Rendering Index is computed for light sources, so I assume you are referring to daylight transmitted through the various glass samples. In your case, there isn't much to compare since all your CRI values appear quite high. If CRI is the most important variable in your application, then simply choose the highest. If there are other issues, such as cost, that would incline you to lean toward the lower CRI, then you won't be losing too much in this case.   (Back to top)

What mixture of acrylic painiting do I need to achieve a copper tone? (717)
The appearance of metallic objects, like copper, depends not only on the diffuse color, but the color of the highlights. Metals look like metals because their highlights are colored. That means that you can't directly mix a non-metallic paint to have the same appearance as copper. You would need to have a reddish-brown color and then paint a representation of a 3D object that illustrated the metallic highlights. In that sense you could mimic the appearance of a metal.   (Back to top)

Can CAM02 to predict Appearance Correlates of a color on different colored backgrounds? (716)
CIECAM02 is only capable of accounting for changes in the relative luminance of the background, not its color. To account for background color changes you would have to adjust the adaptation white point to be some weighted combination of the color of the light source and that of the background (essentially that is the same as incomplete adaptation to the background).   (Back to top)

Is it proper to state a Munsell notation for a metallic or pearlescent color, or is Munsell a solid color only notation system? (715)
It can be done, but it should be done with great care. With metallic or pearlescent materials, the color changes with changes in illumination and view angles. Thus, if you wanted to use Munsell notations for such materials, they too would have to change with illumination and view angle and the material would have quite a large number of Munsell notations.   (Back to top)

Is it possible to draw plankian line in CIE diagram? How? (714)
Yes, it is possible. The full procedure would be to use Planck's equation to compute spectral power distributions for a range of color temperatures and then compute the desired CIE coordinates from those spectral distributions. This is described in several places in Wyszecki and Stiles reference book, "Color Science". Conveniently, they also have a table of the xy chromaticities for a range of Planckian radiators in chapter 3 of that book.   (Back to top)

Is there any source of spectral reflectance data for samples in the Munsell Book of Color? (713)
I don't know of any and the reflectances are not uniquely defined, so different books might have difference reflectance properties (while still having the colorimetry of the renotation).   (Back to top)

Does the Munsell system account for the Helmholtz-Kohlrausch effect? (712)
No. The Helmholtz-Kohlrausch effect is an anomaly in the Munsell system. A gray at value 5 will look darker than a high-chroma color at value 5. At some point in the process of defining the Munsell system and renotation, it was decided that value would be directly related to luminance and that created this issue. It is best to think of the Munsell hue, value, and chroma scales as three independent scales, rather than as a three-dimensional space to avoid this issue. In other words ... only compare value when hue and chroma are constant, etc.   (Back to top)

How closely do the Munsell Renotation data reflect the actual tristimulus values of samples in the Munsell Book of Color as viewed under Standard Illuminant C? (711)
The Munsell samples are made to very tight tolerances with respect to the Munsell renotation data. There is some indication of this accuracy level mentioned in the Munsell books themselves.   (Back to top)

Why does the sheen of a finish affect the appearance of a color? Do the wavelengths of color get magnified, refracted, or intensified as the pass through the layers of a paint film? (710)
The overall perception depends on both the diffuse reflectance of the material (what we often call color) and the surface properties (sheen or gloss, which is not colored). For a glossy material, all that surface reflection goes off in one direction and we can then see the nice saturated, or dark, color of the underlying material. As the material becomes more matte, more of that surface reflection is scattered in all directions and that results in the material looking lighter and less saturated no matter how it is viewed. Consider a black car and a white car both with equal levels of sheen on the final finish. The black car appears to be more shiny. Here, the sheen of the white is masked by all the diffuse reflection that makes the material look white. In the black material since there is really only surface reflection (the sheen), it is very apparent.

Generally for normal materials, there is no effect on the wavelength composition of the light.   (Back to top)

Can you explain the difference between value and luminance? Is Light Reflectance Value different than luminance? (709)
LRV is related to the percent of light reflected and is proportional to luminance. Luminance would refer to the absolute amount of light, while LRV refers to the percentage that is reflected by the paint regardless of how much light is present.   (Back to top)

I understand that the visible spectrum is comprised of the wavelengths red, orange, yellow, green, blue, indigo and violet. Combined they make up white light. So does that mean that white is then a wavelength too? Do all the other colors/wavelengths add up to something that we recognize as white? (708)
There is actually a continuous range of wavelengths between violet and red. The seven names are just a convenient way to divide up the spectrum. White light cannot be described as a single wavelength, but is instead a combination of many wavelengths. Interestingly, you don't need to have energy at all of the wavelengths to make white (for example some displays can make white out of a combination of red, green and blue wavelengths). To answer your last question, yes, all the wevelengths can combine to make something we recognize as white.   (Back to top)

Does the color of your hair affect it's ability to keep your head warm? (707)
If you are in the dark, it won't matter at all. If you are out in sunlight, then darker hair will absorb more of the sunlight and convert it to heat ... making you feel warmer. However, I would guess that the amount of hair would have a larger influence than the color in most circumstances.   (Back to top)

What's a good reference for information on the Munsell system? (706)
I'd suggest this article from American Scientist to get an introduction to Munsell and his system along with references to more details.   (Back to top)

Where can I buy Color Standard for measurement calibration? (705)
Measurement standards are general sold by national standards laboratories such as NIST in the USA, NRC in Canada, and NPL in the UK. There are also companies that sell more affordable secondary standards that are traceable to the national labs. If you do a Google search on terms like "reflectance standards", you can find a lot of information.   (Back to top)

To measure process color is it better to use a spectrometery or density, hue, and gray? (704)
It is better to use spectrophotometry if you are interested in measuring the color appearance, but it might be better/simpler to measure density if you are only interested in the amount of ink present (and you don't measure different types of inks). Densitometers are designed to measure amounts of colorant (ink, dye, pigment, etc.) and not what the color looks like to humans. Spectrophotometers can be used to provide colorimetric parameters that correlate more closely with human perception. Thus, if you are measuring different sets of inks or different types of materials it is possible for density readings to match when the color doesn't.   (Back to top)

Where can I find absorption or reflectance data for inorganic chemicals or pigments? (703)
Sorry, I don't know of any specific source for such information. The best I can suggest is contacting some of the pigment manufacturers to see if they have data they can share or suggestions about where typical data can be found. You might also inquire with these folks. I'm not sure if they include spectral data or not.   (Back to top)

Is there an index for the degree of yellowing? I want to characterize the degree of yellowing in trees as an indicator of poor health from aerial RGB photographs. (702)
There are yellowness scales that could be used. For example, there is a description on page 70 of Berns' "Principles of Color Technology, 3rd Ed." You could also look at color changes in a color space such as CIELAB (also described in the same book). The difficulty you will run into is calibration of your system to consistently convert from your RGB images to device-independent colorimetric coordinates. If the imaging system is not stable, or calibrated, you might have more variability in the RGB images than is present in the foliage of interest. Looking through Berns' text (or a similar text on colorimetry) will give you a sense of the issues involved.   (Back to top)

Please give an example of how to begin with a tertiary color,subtract one color and then subtract another color but don't end up with a primary color. (701)
Well, it depends on how you define "tertiary color". There are a few definitions out there. If you define it as a mixture of 3 primaries, then removing two of them will always leave you with a primary. I've also seen definitions that consist of mixing two secondary colors or mixing a secondary with an adjacent primary. So it really all depends on how you define "tertiary" and how you define the "colors" you are removing. It also would depend on how the colors are being mixed.

Looking at the most common definition, a tertiary only has two primary colors in it, so if you remove all of one, and then all of the other, you are left with either black (additive mixing) or white (subtractive mixing) and that would answer your question.   (Back to top)

Where can I buy the Munsell color chart that has the 14 samples used for CRI tests? (700)
Munsell products are sold by GretagMacbeth. I don't think there is a specific chart with all the color rendering samples, but it is possible to by individual Munsell samples.   (Back to top)

Where do the beautiful colors of fireworks came from? (699)
Various chemicals in the fireworks produce colors due their temperature of burning or atomic/molecular emission. There is a nice article on fireworks here and if you go to the second page there is a link with many more details on light and color in fireworks.   (Back to top)

Why does the greenery of parks and gardens look beautiful to our eye? Please elaborate with regard to perception and function of the eye. (698)
Those same green colors might look quite ugly in a different context. It is the context of the objects, their setting, their meaning to us, and our associations of colors with all of those features that helps us perceive beauty. Ultimately, all of those stimuli are being associated with with pleasant experiences. It could also be considered that the perceived beauty of the plants is an evolutionary advantage for them because it encourages humans to take care of them.   (Back to top)

Do you a reference for this equation used to get color decimal value from RGB values: "color_code = (r*65536) + (g*256) + b" (697)
I don't have a reference for that equation, but looking at it what it is doing is converting 3 8-bit RGB values (0-255) into a single 24 bit number where B is encoded as the least significant 8 bits, G the middle 8-bits, and R the most significant 8 bits. If that number was then expressed in hexadecimal notation, you would get the normal hex color codes that are used on the internet.   (Back to top)

How precise areMunsell color charts meant to be read? (696)
One step in Munsell Chroma is approximately 5 CIELAB units (very approximately). In general , people accept that approximately 1.0 CIELAB unit is a visual threshold (again very approximately and dependent on the color in question). Thus, observers should be able to fairly reliably discriminate about 0.2 Munsell Chroma steps under the best of viewing conditions. So what are the best of viewing conditions? A nice bright daylight booth with fairly large samples set up right next to each other.

Now, I've seen a few of the Munsell soil books, and generally they are ... "soiled". I would be very surprised if the samples in the real world could be considered precise to much better than one Chroma step. On top of that you need to factor in the varying lighting and observers. Certainly with all those variables there is no way the judgements can be considered precise to 0.1 Chroma step. Your "opposing viewpoint" is the one that makes sense to me as a color scientist. It is certainly in line with what I would expect if I was doing the judgements.   (Back to top)

What makes colors fade in plastics? What part or parts of the light spectum? (695)
A precise answer would depend on detailed properties of the material, but it is probably fairly reasonable to say that any of the wavelengths absorbed by the material will contribute to its fading. Thus, the wavelengths most strongly absorbed are probably doing the most relative damage.   (Back to top)

Are there any instruments or methods which measure the intensity of gray color? (694)
Yes. These measurements are usually performed in the field of colorimetry using instruments called spectrophotometers. Spectrophotometers measure the percentage of light reflected by an object and then the results are used to compute colorimetric coordinates. In the case of grays one could use the Y tristimulus value to look at the relative luminance of the grays or the CIELAB L* parameter (which is a nonlinear transformation of Y) to have a number that correlates better with perceived lightness. All of this can be found in more detail in texts on colorimetry such as Berns' "Principles of Color Technology, 3rd Ed."   (Back to top)

What the physical meaning of sharper cone reponse in CIECAM02? (693)
There is no direct physical meaning to these sharpened responses in terms of cone responses. They are not cone responses at all (as is clear from the negative parts of the curves). Instead, they represent combinations of cone responses that could potentially exist at higher levels of the visual system. The result is that these responses, together with multiplicative normalization, seem to fairly well model the overall processes of the visual system. Sharpened responses produce a chromatic adaptation transform with predictions closer to perfect "color constancy" and it makes sense that von Kries scaling in the actual cone responses combined with other mechanisms of adaptation at higher levels would also result in such responses.   (Back to top)

How do paint colors affect the room temperature? (692)
The paint color probably doesn't have a huge physical effect on room temperature overall. However, when there is plenty of light in the room, darker colors will absorb more light and convert that to heat so there could be some effect. There might actually be larger perceptual effects. Some colors are perceived to be cooler than others (but this will vary from person to person) and therefore people might feel that the temperature is higher in a red room (a warm color) than a blue room (a cool color). I have heard that this perceptual effect can be significant (and applies to lighting color as well).   (Back to top)

How can I mathematically find the best match for a CMYK color from an array of CMYK colors?As you have discovered, this is not an easy task. What you really want to do is convert your CMYK colors into a perceptual color space like CIELAB and then use color difference equations to find the nearest selections. This would require either some for of characterization or profile of your printing system.As you have discovered, this is not an easy task. What you really want to do is convert your CMYK colors into a perceptual color space like CIELAB and then use color difference equations to find the nearest selections. This would require either some for of characterization or profile of your printing system. (691)
As you have discovered, this is not an easy task. What you really want to do is convert your CMYK colors into a perceptual color space like CIELAB and then use color difference equations to find the nearest selections. This would require either some for of characterization or profile of your printing system.   (Back to top)

I have some images taken with a digital SLR at the wrong white-balance setting (tungsten instead of daylight). Is there a fixed set of RGB correction factors that I can apply to the entire batch? (690)
Unfortunately not. There are nonlinear steps between the in-camera white balance adjustment and the final output image. Thus it is not possible to obtain the same results after the fact with a simple RGB scaling (unless you happen to have camera raw data, which is saved prior to white balance and other processing). This is illustrated by the fact that you can't get satisfactory results by trial and error. You probably can come up with a reasonable set of RGB scalars, but the results won't be the same as images collected with the proper setting. I'd suggest finding one image of the set that has something that you want to make neutral and using that to get approximate factors to apply to the rest as a first step.   (Back to top)

Why do boys choose blues, grays, black, and browns when coloring and girls choose more brighter colors like greens, reds, oranges when coloring? (689)
I don't know of any research on the topic. There is some information on color popularity on the Crayola website, so there might be some information there. I would suspect the preferences are not well separated by gender at a young age.   (Back to top)

Do some people, through genetics, have dramatically different "rods and cones" in their eyes and see colors totally differently than "most people". This does not include colorblindness, but that some people might see red as yellow and blue as orange, etc. Is this true? (688)
I am not aware of any research that would suggest such unique visual systems, so to answer your question I'd have to say "no" it's not true. Beyond typical color vision deficiencies, there are small genetic differences in the color sensitvities of the three cone types, but these are very small differences and nothing that would produce qualitiatively different visual percepts (like seeing blue as orange, etc.). Of course, we can never be sure that everyone's internal perceptions are identical, but there is plenty of evidence to suggest that our overall responses to color stimuli are very similar.   (Back to top)

I am trying to establish a color system criteria for silicon parts which are white. What do you suggest in setting up a criteria for the color white? (687)
I'd suggest treating it like any other color. Choose a standard to aim for and characterize it colorimetrically (perhaps under multiple light sources) and then use your knowledge of the process and/or customers to set reasonable tolerances in CIELAB coordinates or using a color difference equation. There's nothing unique about white to make this procedure different than it would be for any other color.   (Back to top)

What is meant by plankian locus? What is its importance? (686)
The Planckian locus is the curved line on a chromaticity diagram that represents the colors of Planckian, or blackbody, radiators. As a blackbody radiator is increased in color temperature, its color changes from red, through yellow, to blue and the Planckain locus maps out this change. These color temperatures are also used as descriptors of the colors of other types of light sources. I'd suggest you read about blackbody (Planckian) radiators, color temperature, and correlated color temperature in a text on colorimetry such as Berns' "Principles of Color Technology, 3rd Ed."   (Back to top)

Are there any estimates of the probability that a photon impinging upon a cone photoreceptor will be absorbed by the visual pigment within the receptor? How does this probability change as the radiance is increased so that more of the pigment is in the bleached state? (685)
This question is not as easy to answer as it might seem. I am not aware of any specific estimates. For the optimal conditions with a cone dark adapted, optimal wavelength, etc. the probability that a photon incident directly on the cone will be absorbed is probably quite close to 1. That probability would gradually reduce to zero as the photopigment is bleached, but it takes an extreme amount of exposure to bleach a significant amount of photopigment. The real limits on visual perception are actually getting the photons to be incident on the cone in an optimal way. The probability would depend on the direction and location of the photon in addition to its wavelength. The classic work of Hecht, Shlaer and Pirenne, "Energy, Quanta, and Vision", The Journal of General Physiology 25, 819-840 (1942) describes how photons are lost in the visual process and how single photons incident on each a collection of rods are adequate to produce a visual response. It is generally accepted that cones are only slightly less sensitive to light, but respond individually, rather than in groups and therefore need more photons in a single receptor. You might also look at this website for a brief overview and chapter 7 in the classic text "Vision and Visual Perception" edited by Graham also provides some more details.   (Back to top)

Can a person with a color deficiency learn colors and shades and be able to distinguish differences even if they are not able to see the exact color that a normal vision person might see? (684)
Yes. Many color deficiencies still allow the observers to see quite a range of colors and learn to associate appropriate names with those colors. There will still be some cases where there is confusion (depending on the particular deficiency), but it is really quite amazing how well people can get by. You can learn some more and see some images at vischeck.com.   (Back to top)

Would it be possible to correct color blindness (for computer users) by measuring a user's color sensitivity at various wavelengths, then adjusting the output of the monitor to compensate for it? (683)
Unfortunately not. For some observers, a simple boost in one of the primaries might help, but it is more likely that their own mechanisms of chromatic adaptation have already taken care of that. For dichromats, they are missing one of the cone responses and there is nothing you can do with the stimulus to correct for that. The best you can do is make sure that the stimulus doesn't contain colors they would confuse with one another. You can find lots more information on this topic at vischeck.com.   (Back to top)

How do I calculate whiteness index (WI by ASTM standards) if I don't have a spectrophotometer but am in possession of reflectance data for materials that have <95% reflectance @ 600nm? (682)
I would recommend two texts to get more information on whiteness indices and colorimetric computations. These are Berns' "Principles of Color Technology, 3rd Ed." and Hunter and Harold's "Measurement of Appearance, 2nd Ed." The general form for computing a whiteness index is:
W = Y + 800(xn-x) + 1700(yn-y)
where Y is the sample relative luminance (Y tristimulus value), x and y are the sample chromaticitiy coordinates, and xn and yn are the white point chromatcities. The Yxy values can be computed from your spectral reflectance measurements using standard colorimetric procedures described in the texts. You might also want to refer to the original ASTM standard for more details.   (Back to top)

I am a massage therapist trying to do research on what color is best to have in a massage room and how it affects the client, such as improves relaxation, promotes healing. Any guidance? (681)
There is no single answer. It would really depend on the particular client. You are probably best off with a muted color (near neutral) that is not likely to seem offensive to anyone. Blue is the most popular color as a "favorite color", so maybe a grayish-blue would be good. You then will probably have the best results by allowing the client to decide the lighting level (again keep the color fairly neutral to avoid being offensice). Personally, I would close my eyes and the color of the walls wouldn't matter at all.   (Back to top)

Does a sheet of colored glass reflect, refract or absorb light? Or all 3? (680)
Yes, it does all three. It will reflect light at its surface, refract the light that enters the material, and absorb some of that.   (Back to top)

Could you possibly tell me the formulas for the harmonic equivalents (tones) of red, orange, yellow, green, blue, violet? (679)
To my knowledge, there is no scientifically valid link between color and pitch. However a lot of mythology and non-scientific theories exist. You might choose one of the relationships described on this web page. harmonics.com.   (Back to top)

I need a fairly fool-proof way for a moderately skilled technician to measure a large number of samples and present the data using the CIECAM02 coordinates. I am willing to buy a new instrument/software. Any thoughts? (678)
There are some examples of research code available on the internet. One option would be to adapt one of those to your needs and write the code in house. Since you are willing to buy a new instrument, it might be easier to convince the manufacturer to add the code to their system, if someone hasn't already. To my knowledge, vendors often add features to their software to make a sale. I'd suggest checking with several manufacturers to see if one hasn't already added CIECAM02, or would be willing to to get your business.   (Back to top)

Is pink a shade of red? (677)
Generally "shades" are colors produced by adding black to the color and "tints" are those obtained by adding white (in a subtractive system like paint). Thus, pink would be considered a "tint" of red and not a "shade". See practicalpainting.com   (Back to top)

I am studying the colour of abalone shells. How can I statistically differentiate cbetween two shells? Eg: this shell is bluer than that one. I plan to use digital photos, D65K light with the camera at the normal angle. (676)
As long as you keep your illumination, geometry, camera settings, and processing constant, then the LAB values in Photoshop would be adequate for your purposes. As far as statistics, you can use any normal statistical test on the LAB data. I would, however, suggest using multivariate tests on all three dimensions at once. You might also consider reducing your data down to color differences between shells (or some other standard). The equations for color difference computations can be found in any good text on colorimetry such as Berns' "Principles of Color Technology, 3rd Ed.".   (Back to top)

Does the color of one's eyes (light colored vs dark color) have any effect on vision? (675)
There is no evidence that eye color has an effect on visual performance.   (Back to top)

Can the color of the bedroom walls prevent proper sleep? My husband sleeps fine in a blue room, but has trouble in a red room (same bed!). (674)
Can the color of the bedroom walls prevent proper sleep? My husband sleeps fine in a blue room, but has trouble in a red room (same bed!).It is possible, but not likely just becuase of the color stimulus. For example, if he entered a room that was already dark he would have no way to know the color and it could not possibly affect his sleep. However, that is not the case here. I am sure he knows the color before he tries to sleep and it might have some impact. Perhaps he is just less comfortable in a pink room. Since you have asked the question, this might indicate that it is an issue for him (for whatever reason). Also, you shouldn't necessarily jump to the conclusion that it is the color since I am sure there are other things that are different about the two rooms ... it might be something else. Some even think the direction the bed is pointing matters.   (Back to top)

Are car color choices determined by age, gender or ethnic group? (673)
Almost certainly "no". There would definitely be societal preferences and since people often tend to group themselves according to the dimensions you listed and "like what their friends like", you could probably find some correlation. However, it is quite rare that someone purchases a car that is their preferred color. First of all, not that many people special order a car. Instead they purchase what is on the lot and available for a perceived better price. Secondly, most cars only come in a limited range of colors. These two facts of the automobile market mean that measures of the colors sold and peoples' preferences bear little relationship to one another. It is an interesting topic and there are those who spend a lot of time "predicting" what colors people will like in forthcoming products. However these predictions are self-fulfilling prohpecies since the manufacturers use the predicitons to put the products out into the market and people are forced to purchase what is available. They will capture longer-term trends, but not short-term predictions. One organization involved in this sort of market research is the Color Association of the U.S. See colorassociation.com to learn more about them. Also, here ppg.com is an interesting article on recent automobile color preferences, or at least sales numbers. One other thing to note is that dealers like to stock "conservative" colors like white, silver, gray, etc. since they are more likely to be "not objectionable" to a larger group of potential buyers. I might prefer red, and you green, but we both might be OK with silver.   (Back to top)

What is linear tiff data. What does it record? (672)
Generally when someone refers to linear TIFF data, they are saying that the image data (normally RGB) is encoded linearly with respect to the amount of light in the scene (be it real or synthesized). Since most displays are nonlinear, it is common for image data to be nonlinear to compensate. Thus normal images are nonlinear, but in some applications it is more useful to have linear image data.   (Back to top)

What are the differences in perception of color by males and females? (671)
The most significant difference is in terms of color blindness. Color blindness is a sex-linked genetic trait that is carried by women and normally expressed in men. So while about 8% of males have some form of color vision deficiency, there are almost no females with color vision deficiencies. There are a few other differences, but they seem to have little meaningful impact on perception. For example, it is possible for a woman to have 4 types of cone receptors instead of the "normal" three. However, there is no evidence that they make any special use of them. Their color vision is still trichromatic (3 dimensional) and the fourth type is very similar to one of the others anyway.   (Back to top)

Does the color of glass effect the index of refraction? (670)
Generally, it is assumed that colorants in glass do not affect its index of refraction. However this cannot possibly be true. Depending on the type of colorant and how it is dispersed within, or on top of, the glass, it is almost certain to have some effect. I suspect the effect is often quite small however, but it could be very significant if colorant concentrations were high.   (Back to top)

Why do colors abosorb and/or reflect heat? (669)
That's similar to asking why colors are colors? The chemical structure of atoms and molecules allows them to interact with different wavelengths of electromagnetic energy differently. Some absorb, some transmit, some reflect. There is nothing else that can happen to the energy. I can't say "why", that's just the way nature works.   (Back to top)

What trends are typical when Munsell testing a group of people? Are there effects due to age, gender, education, or ethnicity? (668)
I haven't noticed anything systematic like that in our testing over the years, but we haven't looked for such effects either. You might inquire with the folks at GretagMacbeth about whether there are data on such effects (much of this sort of thing is described in the manual that accompanies the tests). I've never seen data on age vs. results, but as people age their lens yellows, so that would suggest that the blue colors would become harder to discriminate with age. However, a little more light in the blue end of the spectrum might counteract that effect. That brings me to one thought on your results. You might be seeing a systematic trend to more errors in the blue due to some aspect of your viewing conditions being different from normal (e.g., maybe your daylight sources are at a lower correlated color temperature or the luminance is low). There are definitely more errors at lower luminance levels. There should be no correlation with ethnicity or education, but there can certainly be a correlation with motivation. Could it be that your observed correlations are really correlations with some other variable, like motivation to perform the test. If one is not interested in it, they can have wonderful color vision and still score quite poorly.   (Back to top)

Why doesn't Pointer's gamut (CR&A, 1980) fully cover all real points in Munsell system as defined by real.dat? (667)
You should look at the Munsell colors in the file "1929.dat" on style="#0000aa"> available here, to compare reasonably with the Pointer gamut. Those in "real.dat" are not necessarily "real" at all. Those are any colors within the MacAdam limits. Those limits were defined by theoretical reflectance spectra that are 100% or 0% at every wavelength. This range is far more saturated than any object colors that can actually be made. The Pointer gamut is accepted as a reasonable approximation of object colors that can actually be produced.   (Back to top)

I heard that HDMI for HDTV's can have billions of colors but I also heard that our eyes can only see around 10 million colors. Does this mean all that extra color doesnt matter or will it seem clearer in some way? (666)
The number of colors you can see at any given instant is fairly limited, perhaps in the tens of thousands, but your visual system is capable of adapting to different viewing conditions to make those tens of thousands depend on what is around them. For example, in a very dark scene in a movie, you might be able to distinguish many dark colors that would all look alike in a bright scene. There are also issues about how the color information is encoded, processed, and displayed that make those seemingly extra colors helpful. The bottom line is, yes, the added capabilities do indeed improve image quality.   (Back to top)

What color do most people answer when asked to name a color quickly? (665)
I am not aware of any research on that specific question, although some might exist. This website suggests that the answer might be "red" since it is usually the first color name to evolve in a language after black and white. That makes some sense and is based on classic work on categorical color naming by Berlin and Kay. Another reasonable guess might be "blue" since that tends to be the most popular "favorite" color. You might also look into the research in this paper (Boynton, R. M. and Olson, C. X. (1987) Locating Basic Colors in the OSA Space, Color Research and Application, 12, 2, pp. 94-105.) in which people were asked to name colors as quickly as they could and people were quicker and more consistent when the using Berlin and Kay's eleven basic color terms.   (Back to top)

How can I get spectral reflectance information about Color-Aid samples? (664)
Unfortunately, I don't know of any source for these data. The best solution would be to buy a set of Color-Aid samples (very inexpensive) and then measure them with a spectrophotometer (unfortunately relatively expensive). Perhaps you can find someone that will allow you to use a spectrophotometer if you don't have one readily available.   (Back to top)

Is there any standard by which Munsell colors are called "light" or "dark" or are those terms that are too subjective so that they don't get used? (663)
I'd suggest that you take a look at the "ISCC-NBS Dictionary of Color Names" for the most systematic relationship between Munsell designations and common color names. It is out of print, but can often be found from used book sellers and in libraries. Also, to clarify, in Munsell Value 0 is perfect black, Value 10 perfect white, and Value 5 a middle gray perceived to be halfway between white and black. Thus anything above Value 5 would be a light gray until it is called white (maybe above Value 8 or so) and anything below Value 5 is a dark gray until it is called black (maybe below Value 2 or so).   (Back to top)

Do you know of any freely available color matching software? (662)
I am not aware of any free formulation software. The website matchmycolor.com does provide an inexpensive subcription solution. Other than that, you can obtain "free" software from many of the instrument manufacturers when you purchase an instrument.   (Back to top)

sRGB has a gamma of 2.2. Why do the equations have an exponent of 2.4? (661)
The simple answer is that the equations include both linear and power function parts and in combination they approximate a simple power function with an exponent (gamma) of 2.2. In other words, the 2.4 in the sRGB equations is not a "gamma" since it is part of a more complex function. Here is a more detailed explanation.   (Back to top)

Can you comment on how does the following colors affect human psychology when considered in relation to fashion designing: red, yellow, blue, green, orange, violet, brown, pink, white, black, grey? (660)
The psychological/emotional effects of color in any context (fashion design or other) are not really that systematic and precise. There is no question that there are psychological responses to color, but they are very individual and come from different learning situations (e.g., society, personal experiences, etc.). You will probably be able to find books that give you whatever answer you want for the colors you listed. I'd recommend taking a look at Faber Birren's "Color and Human Response" to get a well-written and technically-balanced summary of these types of effects.   (Back to top)

Are there any filters that can be placed over the eyes to make a substance, which is invisible to the naked eye, visible through the filter? Can you give an example? (659)
Sure, there are plenty. For example you could print a fine pattern in yellow on a white background that would be normally invisible and then view the object through a blue filter which would make the yellow areas very dark. My daughter has a game that has hidden answers unless you look through a red filter. The text is cyan on a white background with a high-frequency red masking pattern on top of it. The red filter makes the white and red match (the masking pattern goes away) and the text becomes plainly visble. You could also use metameric pairs that match for a certain viewing condition. When the viewing condition changes (i.e. you look through the filter), the colors would become discriminable. Lastly, you could use a fluorescent material and then changes in either the illumination, or the illumination with filtration could make the material visible.   (Back to top)

Can you provide me with a formula for RGB values given Munsell coordinates? (658)
Actually, I can't. First of all, RGB is not defined and depends on the monitor, operating system, etc. Even if you had calibrated RGB, there are still no formulas to convert to/from Munsell. A lookup table is required. GretagMacbeth provides some conversion freeware and you might also look at the tools at easyrgb.com to get some approximations.   (Back to top)

Is there a range of Munsell or L*C*h coordinates that would describe browns? (657)
Yes, there is a range, but I don't know of a strict definition. I would recommend a very interesting paper on the topic (CJ Bartleson, Brown, Color Res. Appl. 1, 181-191 (1976)) that includes scaling of brown and defines the boundaries of brown in Munsell space. You could also just have a few people look at samples and estimate boundaries yourself. You might also take a look at the "ISCC-NBS Dictionary of Color Names." It is out of print, but an internet search may find copies.   (Back to top)

With all things being equal, is there any reason to see an increase in black dot gain simply by changing the print sequence from CMYK to KCMY? (656)
Yes! There is every reason to think that the absorption and spreading of the black ink would be very dependent on what ink (or lack thereof) has come before. It makes perfect sense that you would see more dot gain if black is printed first since the black ink might spread in the paper more than it would if there were already three ink layers down.   (Back to top)

What is the ideal working space for digital painting in Photoshop and painter is. I tried using Adobe RGB but my reference images look so saturated. (655)
The "ideal" space depends on the user and application. If you are finding Adobe RGB results in images that are too saturated, you might try sRGB, which has less chromatic primaries.   (Back to top)

What color is best to paint a room with hardwood floors to enhance productiivity? (654)
There are plenty of theories on these sorts of things, but very little hard science. I would say that the best color is one that makes you comfortable and keeps the room fairly bright (but not uncomfortably so). When there is more light, you see better, there is less eye strain, etc. and all of that should make you more productive. It also saves energy since lighter paint will reflect more light and require less output from your lamps.   (Back to top)

Is there a guideline, perhaps application-based, for the number of patches needed to make adequate ICC profiles for printer output? Is there an upper limit on the number of patches beyond which more patches do not necessarily improve the ICC profile? (653)
There are no set rules. I have heard of people being successful with 5x5x5x5 sampling of a CMYK process (or 5x5x5 for CMY) as long as they are careful in selecting the samples and in how they interpolate between them. It is not unusual to measure as many as 11x11x11x11 to build a good profile. The number required really depends on the printer's behavior (e.g., linearity, stability, etc.)   (Back to top)

I am looking for products to protect my eyes from UV-C light (254 nm). What substances are opaque or reflect to UV-C light? How harmful is UV-C light to human skin and eyes? Can you suggest any protective measures I should take? (652)
I did a google search on "UVC Safety" and found many products and a lot of information. UVC is extremely harmful radiation, so you should be careful with it and take every possible precaution. In nature, it is absorbed by the atmosphere and does not reach the Earth's surface. In human hands it is used to do things like kill bacteria because it is so good at destroying biological tissue. Apparently it can even cause changes in DNA structure. Here is a link to a document that outlines some safety procedures. Good luck with your work and be careful; protect both your eyes and your skin.   (Back to top)

hat is the correlation between Hunter whiteness (L, a , b) and CIE whiteness (L*, a*, b*)? Can I relate them mathematically? (651)
The HunterLab and CIELAB color spaces to which you are referring (they are more than whiteness metrics) are both computed from CIE XYZ tristimulus values for the sample and the illuminant. To go from one to the other, you would need to invert the first space to compute the sample XYZ values (assuming you know the illuminant values) and then use the normal forward equations for the second model. These could probably be concatenated into one set of equations, but I have never seen that and there would be little benefit. I would recommend Hunter and Harold's "Measurement of Appearance, 2nd Ed." as a good reference for details on these spaces.   (Back to top)

I have a Minolta 2600d portable spectrophotometer. Can you tell me the best way to measure the fluorescence of teeth in vivo? Also, can I use the 2600d to measure the opalescence of both natural teeth and dental materials? (650)
The KonicaMinolta website doesn't give many details on that instruments and I am not personally familiar with it. However, the website does mention UV adjustment, so I assume it is possible to make measurements with and without UV energy in the illumination. Such measurements are one way to evaluate fluorescence. Any difference between the two indicates that the UV energy is being absorbed and re-emitted as visible light through fluorescence. As far as measuring the color of fluorescent materials, keep in mind that the measurement is only valid for the light source in the spectrophotometer. (The website doesn't say, but often these are D65 simulators.) I assume by opalescence, you mean changes in color with changes in illumination and view angle. There is little you can do with this particular instrument, but you could compare the specular component included and excluded measurements to see if there are any significant color changes across that change in geometry.   (Back to top)

Is there a certain color that has been proven to be least tiring to the eye on web page backgrounds? (649)
I don't know if any research has been done on web pages specifically, but it is well established that dark text on a white background is least fatiguing for extended amounts of reading. That's why most computer systems arrange the text that way. For presentations in a darkened room (and short amounts of text), bright text on a dark background is easiest to read.   (Back to top)

What are the calculations used to convert spectrophotometric spectral data to density, CIE XYZ, and RGB variables/values? (648)
All of these calculations share the same basic structure. You take the spectral data, weight it (multiply) by a set of responsivity functions, and then integrate to get the result. In the case of density, you do a logarithmic transformation after the integration and in the case of RGB, you have to do a nonlinear transformation (often) to account for display properties. The weighting functions are different in each case. The best way to learn about these calculations is through a good text such as Berns' "Principles of Color Technology, 3rd Ed." and Hunt's "The Reproduction of Colour, 6th Ed.".   (Back to top)

Why can't humans see colors that fall in the UV or IR part of the electromagnetic spectrum? (647)
It is difficult to answer briefly, but it has to do with the visible range of wavelengths being were a lot of the important information about our world is and with the reactions of biological tissue to electromagnetic energy. UV is damaging to tissue and is best absorbed to protect us rather than being used in our visual system. IR is also produced emitted by warm objects, like our bodies, and it is difficult to overcome this background emission (noise) to detect IR signals in the world.   (Back to top)

Could you please tell me the equivalent Federal No. (Std 595) for Munsell No. 2.1 YR 5.6/16 (Orange)? (646)
I don't know of a conversion table, so I really can't ... but looking at this page, the only orange that is close is FS 32473. You can buy the FED-STD-695 fan deck at chassis-plans.com and make a visual match to a Munsell book. Again, looking at that page (and my Munsell book) I would say that the only one that is close is FS 32473.   (Back to top)

How can I convert NCS color mode to RGB mode in Photoshop? (645)
The NCS system is not defined by any equations that could be used to directly relate it to RGB (or other color specifications). The conversion would have to be made via look-up table. NCS provides some products and software that might help. See ncscolor.com.   (Back to top)

Can you explain how detergents would cause color fading? (644)
Fading from detergents can happen in several ways, but the most likely causes are simply that the detergents are removing the colorants (chemicals producing the color stimulus) from the material or that the detergents are facilitating a chemical reaction that changes the colorants into a form that is colorless.   (Back to top)

Do HSV and HSI refer to the same model? If not, what is the difference? (643)
They are slightly different and both examples of "color spaces" derived from device-dependent RGB color specifications that bear no real relationship to accurate colorimetry or color perception. They are very gross approximations, but sometimes more useful than the simple RGB specifications. You can learn more about them in texts on computer graphics or get a quick overview here.   (Back to top)

How often should color vision testing be assessed if the ability to see colors is important in one's occupation? (642)
Most color vision deficiencies are acquired and do not change through our lifetime. For those cases, once is enough to diagnose the presence or absence of a color vision deficiency. If you are interested in color discrimination ability (e.g. some of the information given by the Farnsworth-Munsell 100-Hue Test), then that can change with both age and motivation. I would suggest that doing that exam once every two years or so would be more than adequate. (As a note, I have done the test for more than 20 years and my results have not significantly changed when I am motivated to do the exam carefully.)   (Back to top)

I would like to make a children's computer program emulating colour mixing of paints. Since coputers generally use the RGB colour model, I don’t know how to achieve this. Can you help? (641)
The technical details of paint mixing are quite complex, but you can make an approximation with simple subtractive mixing. The trick will be to convert from the subtractive model for paints to the additive model for your computer program. What you need to do is abstract the color combinations in the subtractive model and then convert the result to RGB. For example your "blue" paint is generally really a cyan color (G + B to display it) and yellow is G + R. If you did additive mixing of lights, then the result would be R + 2G + B (just add up the values). However, a subtractive mixture behaves differently. You have to look at the light that is missing. The cyan has removed the R and the yellow has removed the B, so starting with white (R + G + B) and removing those amounts you end up with (R+G+B) - B - R = G (the green you are looking for). You then have to factor in various amounts of these mixtures.

I hope that is helpful. There are also some demos at the SDC Colour Museum website. You have to click on the little floating icon to get to the demo.   (Back to top)

Can chromatic discrimination change over time or can it improve through practice? (640)
It can certainly change over time, but I am not aware of any data that suggest an improvement with practice. What might improve with practice is the awareness of certain attributes or the motivation to be concerned with the differences. The raw color discrimination capability doesn't improve with practice, just the ability to do related tasks.   (Back to top)

Any correlation between age and chromatic discrimination ability? (639)
In general, as we age our color discrimination ability decreases (except for young infants where it is still improving). This is largely due to the gradual yellowing of the lens in our eyes, which also results in more scattering and reduced luminance sensitivity.   (Back to top)

Do any illnesses/physical characteristics/disabilities impact one's chromatic discrimination ability? (638)
I have heard of illnesses or various other injuries impacting chromatic discrimination. For example, there are cases of tumors in certain locations in the brain that cause the patient to have achromatic perception (a black and white world). I don't know much about details, but it is possible.   (Back to top)

How can a color display with three monochromatic lasers produce a finely rendered colorspace, with what seem like the appropriate pastels and everything? (637)
This is because our eyes cannot tell how a stimulus is made. We have three types of cones in our retinas and as long as the energy absorbed in the three types is equal for two stimuli (e.g. a pastel made with paint and illuminated with daylight vs. a pastel made with three lasers, then the colors will match. This is the definition of metamerism, which is the basis of modern colorimetry.   (Back to top)

What are the different textures of colour? (636)
Texture is usually considered separate from color as the spatial distribution of colors, the spatial distribution of gloss, or the spatial distribution of the surface height of the object. Color is normally treated as a distinct measurable value (a perception).   (Back to top)

How can I convert CIELCH to CIE 1931 x,y coordinates? (635)
The first step is to convert CIELAB L*C*h (there is no such thing as CIELCH) back to CIELAB L*a*b*. That is a simple coordinate transformation from the cylindrical coordinates (L*C*h) to the rectangular coordinates (L*a*b*). You will then need the CIE XYZ tristimulus values of the illuminant (which were used to compute CIELAB coordinates). With those, it is fairly straightforward to invert the CIELAB equations to compute the CIE XYZ values of your sample. From there you need to convert XYZ to xy in the normal way. All the necessary equations can be found in any good text on colorimetry such as Berns' "Principles of Color Technology, 3rd Ed."   (Back to top)

What is the utility of converting tristimulus values to L*a*b* values? (634)
Converting to CIELAB (L*a*b*) allows you to better describe what the samples look like, their lightness, chroma, and hue, and to set tolerances for the production of those colors (i.e., measure color differences). It is another way to represent the same information, but it is a potentially more useful way.   (Back to top)

Can my company's color references be accurately reproduced 10 years from now based on the tristimulus values we maintain ? (633)
Your references will be quite stable over 10 years. The CIE just celebrated the 75th anniversary of the 1931 system and it is still very widely used and will certainly be around for a good long time. No worries there.   (Back to top)

How do the eye and the brain work together to create the chromatic adaptation 'illusion' effect with colours? Also, why does looking at certain stimulus for certain lengths of time effect the time span of the adaptation? (632)
Here's a nice little demo of chromatic adaptation .

To try to answer your question. The eye accomplishes chromatic adaptation through adjustment of the sensitivity of the three types of cone receptors based on their previous exposure to light (more exposed to blue, the receptors become less sensitive to blue). This is like an automatic exposure control (or more precisely and automatic white balance) in a digital camera or camcorder. The brain helps by interpreting the world and discounting illumination effects (such as shadows or clearly colored light sources) to help us better recognize objects (which are usually more interesting to us than illumination). This is called "discounting-the-illuminant" and is essentially a sub-conscious cognitive effect (it can be learned and unlearned in certain situations ... normally in the form of illusions).

The time-course of chromatic adaptation is not really dependent on the stimulus. It is essentially complete in about two minutes. However, often when looking at adaptation effects, we don't take the time to fully adapt and the illusion, or after-effect, goes away in roughly the same amount of time we took to adapt. There are some higher-level after-effects that can take longer to go away. You might search on the "McCullough Effect" to learn about one of those.   (Back to top)

What makes wet grass greener than dry grass? A scientific explanation of more than just refractive index would be much appreciated. (631)
Actually, refractive index doesn't explain it very much at all. There is surface reflection at the interface between grass and air that is due to the change in index of refraction (grass different from air). The index of refraction of water is closer to that of grass than air, so it helps the situation. Surface reflection is not colored (not green in the case of grass), but the same color as the illumination. Dry grass has a fairly diffuse surface that scatters that surface reflection in all directions so what you see is a combination of the green (subsurface reflection) plus the white (surface reflection). When the grass is wet, it becomes glossy since the water smoothes the surface. That means all the surface reflection goes off at one angle and becomes a glossy highlight. At other angles all you are left to see is the subsurface (green) reflection and thus the wet grass looks greener (more chromatic) than dry grass.   (Back to top)

What does the ratio b/a give or mean? Here a is negative and b positive. (630)
I assume you are asking about CIELAB a* and b*? The ratio itself has little meaning, but the inverse tangent of the ratio is called hue angle and is a good indication of the color's hue. When a* is negative and b* is positive, you are in a range of hues between yellow and bluish-green.   (Back to top)

Can you provide list of non toxic pigments that are insoluble in water measuring about 1 micron particle diameter? (629)
The definitive list of dyes and pigments (colorants) and their properties is the "Colour Index International".   (Back to top)

I am preparing a 3 band fluorecent lamp powder recipe for color point x=0.312, y=0.336, Ra= 82,SDCM<3. Can you provide any useful recipe development procedures, methods or any useful website for me about the color coordinates adjustment? (628)
This is a very specific application and I would suspect that very little information is in the public domain regarding this topic as it is probably a competitive secret among lamp manufacturers. I am not sure how the fluorescent powders interact, but if you know the color of the individual phosphors (Yxy) then you could predict the color of additive mixutres by simply summing the tristimulus values (XYZ) in absolute units. You could use the same procedure to predict the amounts (or luminance levels) of the three phosphors required to produce your aim chromaticity. This all assumes the phosphors don't interact when they are coated simultaneously.   (Back to top)

Can you help me transfer color temperature to 1931 CIE xy-coordinates? (627)
You would use Planck's equation to compute the spectral power distribution of a blackbody at 6500K and then use the CIE color matching functions to compute the chromaticity of that spectral power distribution.   (Back to top)

I am shopping for a new motorcycle helmet and want to know the color's that would keep my head cooler in the sun. Where do colors such as grey or silver fit in as far as reflecting light/heat and staying cooler? (626)
The coolest (temperature wise) will be white because it reflects all the light. A good shiny silver would probably be close. Black will be the hottest and gray will be in between (probably hotter than silver). For colors, it is hard to say because the color might not necessarily correlate perfectly with heat absorption. However, they will all be hotter than white. Red, for example is nearly as hot as black because it absorbs a lot of energy (all the blue and green light and only reflects the red).

If you really want to keep your head cool ... go with white.   (Back to top)

Is there any research on changing the colors of a light to improve a surgeons abilility to see in different surgical enviroments? Can you improve their contrast sensitivity like skiers do with colored lenses. (625)
I am not aware of any research on this topic and couldn't find any in a brief internet search. It seems the main concerns in surgical lighting are the elimination of shadows, high luminance (improving acuity and color discrimination), and white (best for rendering all colors). A specific color other than white might be helpful for certain types of surgery (depending on the colors of the features being operated on), but it would also change the appearance of everything else and that might make it less comfortable/familiar for the surgeon.   (Back to top)

How do I assign a RAL number to a standard color used by my company? (624)
RAL is a proprietary color naming system. You would have to find out from them how to set a designation. See ral.de.   (Back to top)

I'm measuring several 3000K white lamps. I'd like to know the color variation of these lamps. Is there any other way to measure color variation of a population of lamps, aside from standard deviation and MacAdam ellipse? (623)
You can use the CIELAB color space and color difference equations for lamps, but you will have to make a selection of one to use as a reference white. Perhaps the ideal 3000K lamp could be your reference. You would then use its tristimulus values as the CIELAB white point and the other lamps as stimuli. You could then compute CIELAB color differences between each lamp and the reference, or between various lamps. If there are differences in absolute luminance this computation might get tricky, so I would encourage you to normalize all your lamps to a relative luminance of 100 (any number would do) before the CIELAB calculation. This will result in every lamp having an L* of 100 as well, but you can examine the color differences between the lamps by looking at the a* and b* differences that will remain.   (Back to top)

I require formulation for a Paint that absorbs magnetic rays or RF energy used by RADAR and do not reflect back. (622)
This is not really a color question since absorbing radar and producing color happen at different wavelengths and they need not be related. There is a description of radar-absorbing materials here.   (Back to top)

Is it possible for a liquid subtance to appear clear or colorless when placed on a white piece of paper with the naked eye, but will appear a unique color when seen through a filter? (621)
The only way to do this would be if the substance was opaque (like the paper) and had a spectral reflectance curve metameric to the paper for the first viewing condition, but not metameric when viewed through the filter.   (Back to top)

I am interested in obtaining a very accurate spectral match of my color sample. Some of the color matching systems I have used in various paint stores do a pretty good job of matching the color but not necessarily the spectrum of my sample. (620)
Many, if not all, of the commercial color matching software packages (such as what you find in paint stores) use some form of spectral matching algorithm and such algorithms can be quite effective. However, the only way to get accurate spectral matches is generally to use the same material and colorants as the original. For example, if you were to match house paint with one of the systems in a paint store, you would have a good chance of getting a spectral match. In many cases you don't have the luxury of using the same materials and colorants so you have to settle for a colorimetric match (probably metameric).   (Back to top)

Can you explain which coloured dyes change colour or fade and why when used as a gamma radiation dose indicator? (619)
Well, I don't know anything about this topic (and I don't think it is familiar to anyone else in the lab), but I found this webpage that seems to explain it pretty well.   (Back to top)

What is multispectral image? (618)
"Multispectral" is an ill-defined term in imaging. In general it refers to an image that has more than 3 channels (which are typically RGB) sampling the visible spectrum (and it could extend to other wavelengths as well). When the image is sampled a relatively fine increments through the spectrum (say 20nm or less) with a bandpass equal to the sampling increment, that can be referred to as simply a "spectral image" (just like we talk about spectral reflectance or spectral power distributions).   (Back to top)

What is the problem if a person sees both gold and silver as silver? This person also has red-green defects. (617)
Since you mention that the person has a red-green deficiency, that really answers the question. A red-green deficiency can be consistent with a confusion of silver and gold. Although it would depend on the illumination, the discrimination between silver and gold (which is a color discrimination) could well fall along a line of confusion for a person with red-green color blindness. You might take an image with silver and gold in it and process it through the tools at vischeck.com.   (Back to top)

What is the top that is black and white and makes pale colors when spun? (616)
It's called Benham's top, or Benham's disk. It's easy to find information on it on the internet. Here's an example.   (Back to top)

I would like to perform the Farnsworth-Munsell 100 hue test on my monitor. Will this work? Can I have the values of each colour caps to form the colours? (615)
You could, but you would have to be very careful about monitor calibration/characterization, adapting conditions, and luminance level in order for the results to mean anything. It is probably cheaper and easier to simply buy the real test from GretagMacbeth. I don't believe they publish the color definitions, but there might be some academic papers on the topic with data. I would suggest a search in Google Scholar to see if you can find references.   (Back to top)

I am creating a colorant database for my matching software. How do I reduce the bronzing of Pth Blue at high concentrations? (614)
The usual cause of this is that you have reached too high a concentration of colorant for your substrate and it is coming to the surface. Since this is happening, you are perhaps trying to construct your database at levels of concentration that will not be usable in your final products. You might well be able to build a usable database without going to such high concentrations.   (Back to top)

Which colored paper reflects more light? (613)
White.   (Back to top)

The color of an object depends on the reflection and the absorbtion of light. How? (612)
Actually, the color of an object depends on three things, the light source, the object properties (as mentioned in the question), and the human observer. All three are necessary for an object to have "color." As far as the object itself, it is the property of absorbing different amounts of the various wavelengths of light that impart color to the object. Whatever light is not absorbed is either reflected or transmitted and that is what we see.   (Back to top)

What are good books to get detailed information on both the Munsell and CIE systems? I'm an artist and have a general education of both systems but would like to know indepth knowledge of each, including the math and reasoning behind the constructions of each system. (611)
A good starting point for the CIE system is Berns' "Principals of Color Technology, 3rd Ed." and it also includes some background on the Munsell system. Specifically on Munsell, there is "The New Munsell Student Set" by Long and Luke (which also includes an abridged set of samples) and you can still purchase "A Color Notation: An Illustrated System Defining All Colors and Their Relations" by Munsell and Farnum.

If you want to get deeper into the subject you might look at "Color Space and Its Division: Color Order from Antiquity to the Present" by Kuehni.   (Back to top)

I am building a fiber glass airplane. The kit mfg says paint it any color you want as long as its white due to heat build up in the sun. Any idea of how far off-white I can get? How can I calculate the increase in heat absorbtion if I go a little blue or yellow off of white? (610)
This is not a simple question to answer since it depends on more than just the color. Heat build up will come from light absorption (color), but also from absorption of ultraviolet and infrared radiation (which might have little correlation with color). So the answer can't be given simply in terms of color. However, if you select a paint that is a fairly light shade (near white) as you suggest, then it's properties in the UV and IR are likely to be similar to those of the same type of white paint. That is because there simply is not that much colorant in the paint to make a change at any wavelength.   (Back to top)

Is there a specific color that could be called Munsell green? What is its Munsell designation? I understand this color is commonly used at places like university campuses for exterior electrical equipment enclosures. (609)
I understand why you are perplexed. There is no single color known as "Munsell Green". There is a principal Munsell hue called green that would have the hue designation of 5G. However, even when narrowed down to that single hue, you have many colors because you can still vary value (lightness) and chroma. You would need a designation of all three to have a specific color.   (Back to top)

How is the location of an illuminant on the Planckian Locus and R-G Axes related to colour vision tests? (608)
The illuminant location defines the appearance of white in a given viewing condition. The appearance of samples in a color vision test is then determined relative to the adaptation point. Since these tests are designed to probe certain color discrimination properties of deficient observers, it can be important that they are used with the proper illumination.   (Back to top)

What is the "straight line rule" when referring to the CIE 1931 Chromaticity Diagram? (607)
It refers to the fact that the chromaticity of additive mixtures of two colors fall on the straight line between the chromaticities of those colors. The exact location along that line is proportional to the relative luminance to each of the two colors in the mixture.   (Back to top)

Which RGB values or others make color that is visible only under ultraviolet ray on the white paper? (606)
Making a color that is visible only under UV radiation is not a matter of RGB values, it is a matter of selecting a material that is fluorescent when illuminated with UV, but matches the background under normal visible light. In that case, the RGB values would be the same as the background, but you would only use the fluorescent material for the parts you wanted to be visible under UV.   (Back to top)

If one measures same color on various spectrophotometers the spectral profile is the same,but there are differences of 2-3 % in reflectance. Can you explain why? Which is the most correct reading? (605)
The most correct reading is that obtained by a national standardization laboratory on a reference instrument. Results from different instruments vary for many reasons. These include subtle differences in illumination and viewing geometry, sample area, sample presentation, calibration differences, and systematic errors in the instrument (e.g., wavelength, bandpass, photometric scale linearity, etc.). For fluorescent objects, the light source in the instrument will make a difference as well.   (Back to top)

Can I use BCRA standard tile for calibration of spectrometer? Where can I buy it? (604)
Yes, they are available from the National Physical Laboratory in the UK.   (Back to top)

What are the advantages and disadvanatges of chromaticity diagrams? (603)
The chromaticity diagram provides an abridged method to specify the hue and saturation of an unrelated stimulus or of metameric matches. That is really its only meaningful application. It has far more disadvantages such as having no representation of luminance, having no relationship to appearance, and having perceptually nonuniform spacing. I would recommend a review of the topic in Berns' "Principles of Color Technology, 3rd Ed" for more details.   (Back to top)

Can you please define "dominant wavelength" and "wavelength of maximum absorbance"? Which should be used in the calculation of strength? (602)
Dominant wavelength is a colorimetric measurement from a chromaticity diagram. If you draw a straight line on a chromaticity diagram from the white point through the chromaticity of the sample to the spectrum locus, the wavelength at which this line intersects the spectrum locus is the dominant wavelength. The wavelength of maximum absorbance would be derived from simply finding the maximum on a spectral absorbance function. Dominant wavelength would have no correlation with strength and neither would the wavelength of maximum absorbance. However, the absorbance value at that wavelength might be useful in a calculation of strength.   (Back to top)

I am writing a story about colour for children. Can you help explain (in simple terms) how a rainbow works and how the mixing of just a few colours in printing pictures in papers works? (601)
I like howstuffworks.com for reasonable explanations of many things. That link is for rainbows and I'm sure they have one on printers, too.

As far as a simple explanation, I just like to say the different colors of light are bent to different angles by the raindrops in the air (for a rainbow). For color printing, you can say that we have only three types of color receptors in our eyes and the primary colors in a printer work to control the responses of those three receptor types. Since there are only three receptors types, only three primaries are required.
<>br> Another good source is the "Magic Schoolbus" books on color and the senses.   (Back to top)

Would you recommend a source for standards tile for calibration of spectometer? (600)
There are a series of National Measurement Laboratories around the world, some of which provide standards for spectrophotometry. For example NIST in the USA, NPL in the UK, and NRC in Canada provide these services. I am sure there are others as well. Also, some instrument manufacturers provide calibration services.   (Back to top)

How long does it take to perceive color? Are some colors perceived more quickly than others? (599)
It takes about 1/10 of a second to perceive any visual stimulus. But that is the latency for the signal to reach awareness. But the visual system can follow changes, such as flicker, at very fast rates depending on their color and intensity. So even though there is a lag for the signal to reach consciousness, the visual system itself can follow rapid change.

Your question is hard to answer because the answer depends on the state of adaptation of the eye and the intensity of the flash of light. It really doesn't matter how brief a flash of light is if it is bright enough because the response of the eye is accumulated over time.

But it is safe to say that under certain certain laboratory conditions, one can show that red and green are perceived more quickly than blue and yellow and that white/black differences are the fastest. But under normal viewing conditions, these differences will not be observed.   (Back to top)

I have an RGB digital SLR camera. Is it possible to find relationship between the camera output and the spectral reflectance of objects? (598)
It is possible if you have some more information about the objects. For example the spectral reflectance for many objects can be fairly accurately represented with three basis functions. If you know these three basis functions, then you can use the RGB responses of the camera to determine the necessary weightings to recover a spectral reflectance curve. It would be an approximation in most cases and you can do better with more responses.   (Back to top)

How can I determine color names corresponding to hex color values? (597)
This is easy to figure out yourself (your names are the best for your purposes) since there are several tools on the web for conversion between decimal and hex RGB notations. You just need to parse the hex numbers such that the first two are R, the second two G, and the last two B and use a tool like easyrgb.com to view the colors.   (Back to top)

What is the meaning of NET profiler of a color spectrophotometer? (596)
Netprofiler is a commercial software application sold by GretagMacbeth.

Check the GretagMacbeth site for many more details. Briefly, this application communicates with GretagMacbeth via the internet. Information is exchanged which tries to improves the measurements and maintenance of your spectrophotometer.   (Back to top)

When I measure delta L on low-gloss (matte finish) parts, I notice more variation between measurments than with higher gloss parts. Is there a scientific reason for this? Does the gloss play a roll? (595)
The measurements of the lower-gloss parts might be more sensitive to variations in measurement geometry. That would mean that differences in instrument geometry, sample presentation, sample flatness, etc. would be more likely to add variability to your measurements.   (Back to top)

How can I extract a specified color from an RGB image using Matlab? (594)
There are two parts to this question. First, I assume you have an RGB image file to extract the data from. This file could be output from a camera, scanner, or simply an image you found on the web somewhere. Second, you need to transform the RGB data into a color space, such as CIELAB.

To extract the RGB data from an image file, use the Matlab function imread(). Details on this function can be found on this Mathworks page. This is a smart function which looks at a file and determines which procedure to use to read in the data. It will automatically handle jpeg, tiff, gif, and many other image formats. Imread() will usually return a 3D array, M rows, N columns, 3 image planes. For example: myImg = imread('myImageFile.jpg'); The RGB coordinates of a pixel are myImg[m,n,1], myImg[m,n,2], myImg[m,n,3], respectively.

To extract the actual color of that pixel, you will need more information. If you know the image is from certain scanner or camera, you can derive a characterization for that scanner which will predict CIELAB or CIEXYZ from the RGB data. If you know the data are sRGB, there are transformations to convert the data to CIELAB. If you have no other information about the RGB image file, then you cannot recover the color accurately. RGB values are device-dependent, and without information about the device, RGB data cannot be processed any further.   (Back to top)

How does one go about using use color measurements to determine the concentrations of colorants/dyes in aqueous solutions? (593)
This is essentially the topic of the area known as color, or colorant, formulation. The relationship between colorant concentration and spectral transmittance (in this case) is characterized for all colorants of interest and then an appropriate model (the Beer-Lambert Law in this case) is used to predict the characteristics of mixtures. Given a mixture of known colorants (unknown concentrations), it is possible to figure out the concentrations by inverting the model. Berns' text, "Principals of Color Technology, 3rd. Ed." provides a good overview of these procedures.   (Back to top)

I evaluate llighting systems by measuring u'v' with a spectroradiometer. How can I calculate deltaE color difference from this data? (592)
It is a tricky calculation, but what I would recommend is normalizing the sources to the same luminance (Y=100) and then use Illuminant D50 (with Y=100) as the CIELAB reference point (XnYnZn). Then convert your u'v' measurements for other sources back to XYZ (scaled to Y=100) and use the test source as the stimulus (XYZ) in the CIELAB computation. You can then compute the delta-E between the reference D50 (L*=100, a*=0, b*=0) and your test source (which would be slightly different). This delta-E will be equivalent to the idea of illuminating side-by side white samples with the reference and test sources and assuming you adapt to the reference source. That is a completely valid and meaningful computation to do.   (Back to top)

How is the Light Reflectivity Value (LRV) measured? Why do building codes require a certain percentage of LRV in the materials used? (591)
LRV is ill-defined, but the best metric appears to be the CIE Y tristimulus value (or the luminous reflectance). I am not familiar with the building codes, but I would suspect that it is an issue of energy conservation since lighter building materials would result in less energy required for achieving desired illumination levels and to cool the building interior.   (Back to top)

Do people with light colored eyes have better night vision than people with dark colored eyes? (590)
I don't believe there are any data to suggest that eye color has a significant systematic effect on visual performance.   (Back to top)

Do you know of a color/temperature chart showing various colors and their related heat reflection/absorption properties? (589)
Unfortunately, I am not aware of any such chart and it is unlikely that it is even feasible to make one. Heat absorption properties do depend on color, but they also depend on the material's properties in the ultraviolet and infrared parts of the spectrum and the nature of the illuminating source. So there is no way to consistently match up color and heat absorption properties without knowing other details of the material and illumination.   (Back to top)

What sorts of jobs would a color scientist do? (588)
Thanks for your inquiry. For one thing you made me realize we have to make a page on our website that gives examples of the types of jobs our graduates accept. We do have a page listing our sponsors and companies that students have gone to work for (there is a big overlap between the two).

Most of our graduates at both the M.S. and Ph.D. level end up going into industrial research and development positions. There are a variety of fields represented by the list I mentioned above. Recents grads have ended up working on things like printing/color reproduction of greeting cards at Hallmark, formulation of paints at Benjamin Moore, imaging systems at HP, cell phone cameras at Qualcomm, display systems at TI, electrophotographic printers at Xerox, imaging software/hardware at Apple, television quality at Philips and Samsung, etc. Many have gone on to help found technology companies or to very high level research positions at places like Kodak, HP, Microsoft, etc.   (Back to top)

What is the relationship between the CIELAB a*-b* opponent axes and the perceptual unique hues? (587)
The unique hues do not directly line up with the a*-b* axes. One reason for this that we perceive different numbers of discriminable hues between each of the four unique hues (e.g. we see more purple hues between unique red and unique blue than greenish-yellow hues between unique yellow and unique green). In terms of CIELAB hue angle, the unique hues fall at approximately R:24 deg., Y:90 deg., G:162 deg., and B: 246 deg. Only unique yellow happens to line up with a CIELAB axis (positive b*).   (Back to top)

When the 3 hands on a spinning toy (which are 3 different sizes, long, medium and short) spin around really fast, they leave 3 "trails" of light in concentric circles. Why do we see 3 complete circles of light all the time? (586)
What a great question! The effect you are seeing is called "Persistence of Vision". A web search on that topic turns up a bunch of good explanations. Here is one experiment about it from the Exploratorium.

Essentially, our eyes take a certain amount of time to respond to stimuli in the world. It is roughly 1/30 of a second. So if your lights make a complete rotation in less than 1/30 sec. then your eyes basically add up all the light for that time period and produce a single image (the circle formed in that time period). It's the same reason that things moving quickly look blurred. You should be able to see similar trails of light by just moving lights around with their hands ... the faster they move the lights, the longer the trails. If they make a full circle quickly enough, then it will appear like a full circle of light.   (Back to top)

Why do colors fade in the sun? is it the heat or the light? (585)
There are a lot of causes of fading, but it is probably more common that it is the light exposure more than heat exposure. Beyond that, exposure to ultraviolet energy is even more damaging in most cases (this is the same stuff that gives us sunburns).   (Back to top)

Do humans have a natural affinity for certain sorts of colors more than others as compared to other creatures? (584)
Our affinity for colors is very much influenced by society, so you could say that we do since our society is different. If there are inherent affinities, then they might well be similar for other animals that have similar visual systems (which turn out to be relatively few in number).   (Back to top)

Do insects that have UV sensitivity in their visual system see the UV portion of the spectrum as "color"? (583)
As far as insects, it is really impossible to say for sure, but it seems that there visual systems are designed such that the UV part of the spectrum gets processed as another color response. Of course it is possible that they don't see "color" at all and just use the different responses for different functions (sort of different sets of black and white images for different purposes).   (Back to top)

Is color limited to the interaction of light with an object and our eyes? (582)
Yes, we need to have our eyes involved in color but we do a lot of manipulation of lighting and objects to control those color perceptions. So there is plenty of color science that just involves the light and objects without worrying about the eye too much. You need light and the eye, but you don't necessarily need an object ... lights can be colored all on their own.   (Back to top)

If no light is falling on an object, does it still technically have a "color"? (581)
Color is technically defined as a perception and if there is no light to initiate that perception, then there is no color. So I would say that if there is no light falling on an object it doesn't have a color. If there is light on other objects in the scene, but none on that one particular object, then its color would be black.   (Back to top)

How does a color TVthere is a great website describing how TV works at . work? (580)
There is a great website describing how TV works at How Stuff Works.   (Back to top)

How can I know the spectral sensitivity of a common CCD camera? (579)
You could ask the manufacturer. They might have published specs for the camera and/or sensor. Other than that you can measure them yourself, but it takes a rather elaborate laboratory setup to do so.   (Back to top)

Does the color green inspire thought? (578)
No more so than any other color. Affective responses to color are very real, but they are not consistent from person to person. If green inspires thought in you, that's great, but it might just put someone else to sleep.   (Back to top)

Do objects that are the same color have the same chemicals (elements) present? For example if I looked at the chemicals in red paint would I find the same ones in a red flower? (577)
Generally no. Simply put, there is more than one way to make the same color. For example, grass is green due to chlorophyll, but my color TV can make that same green color with a combination of red, green, and blue phosphors and a color printer can make grass green with cyan, magenta, and yellow inks or dyes that include no chlorophyll at all. There are lots of different materials capable of producing any given color.   (Back to top)

How I can mathematically convert from CIELAB (D65,10°) to XYZ (D65,2°) or RGB? (576)
You can't. CIELAB can be converted back to XYZ using the simple inversion of the CIELAB equations, but there is no way to change from the 10° observer to the 2° observer in the process. As far as conversion to RGB, that requires a characterization for the monitor you are using. A common choice is to convert to standard RGB (sRGB) values and there is a set of equations defined for that conversion.   (Back to top)

How do the colors you wear affect your appearance? What colors make you look certain ways? (575)
Really, the colors you wear affect your appearance however you believe they do. There are no specific scientific rules that apply in all cases. Some people look and feel good in certain colors, while others will have the same experience in completely different colors.   (Back to top)

What is an easy way to create a color scheme using an elliptical path and a Munsell conversion program? (574)
I assume you mean an elliptical path through the color space to select the colors in your scheme. An easy way would be to draw (either by hand or electronically) the polar coordinates of the Munsell system and then select the range of hues, etc you want to traverse and simply sketch out the path. There is no need to have a precise ellipse. You can then select the Munsell notation that your path crosses and use the conversion program to convert those over to RGB, CMYK, or whatever other coordinates you would prefer to work in.   (Back to top)

Is the temperature the same in shadow under a dark colored fabric awning as under a a light colored awning? (573)
As long as you are some distance from the awning and/or their is plenty of ventilation then it wouldn't matter at all. However, a dark awning is going to heat up more (it absorbs light and converts it to heat where the light one reflects most of the light) and then re-radiate some of that heat. Thus, if you are close to the darker awning, or their isn't good ventilation under it, then it will definitely feel warmer under the darker awning.   (Back to top)

Sailors know from experience that darker colored fabrics last longer in full-sun exposure than white or very light colored fabrics. I am specifically referring to Sunbrella bimini and sail cover fabrics. Why? (572)
I am not familiar with the longer lifetime of the fabrics you mention, but it makes perfect sense that the colorants might well protect the fabric itself from harmful radiation (light and UV). The colorants probably end up fading first and then any damage that the light/UV causes the fabric would begin.   (Back to top)

How do grey scale images differ from color (RGB) images? (571)
Grayscale images have one dimension of information for each pixel (light-dark) while RGB images have three dimensions (channels) of information (amount of red, green, and blue). There is a wide variety of methods for deriving grayscale images, but generally they are equivalent to some weighted combination of the RGB channels of a color image.   (Back to top)

How can I match a paint color to Munsell N8? (570)
You could purchase a Munsell N8 sample from GretagMacbeth and then take that to a paint store to be matched. This is usually very effective and accurate. Alternatively, if the store can match a numerical specification, Munsell N8 translates into CIELAB values of L=80, a*=0, and b*=0 under daylight. You might be able to provide these numbers to the paint matcher and they could enter them into their system to formulate the match.   (Back to top)

I'm looking for a Circular Spherical Vision Spectro Colorimeter for analyzing luminance and other parameters (axis etc...) of reflective materials in different colors for road construction. Can you help? (569)
It sounds like you are looking for a 3D goniospectrophotometer. To my knowledge, there are none available commercially but rather research labs custom build instruments for their own use. There are 2D multi-angle instruments on the market that are used for applications like metallic automotive finishes. (2D means that the illumination and measurement angles are always in the same plane relative to the surface.) One example is from Datacolor, but there are others from manufacturers like GretagMacbeth and X-Rite. Perhaps one of those instruments would be helpful for your application.   (Back to top)

Is there a source for a neutral gray paint designed to be used on floors and/or walls in a TV broadcast studio? (568)
I am not aware of a specific standard or source for gray paint for TV studios. If you take a sample of the desired gray to a reputable paint store, they can measure it and produce a very close match. In your situation, and 18% photographic gray card might be a good choice to match. That is a bit darker than typical viewing booths, but I would think a slightly darker surround would be good in a TV studio.   (Back to top)

I would like to find pigments with relatively narrow spectral aborption bands. The goal is to create paint which offsets the peak emission lines of different artifical light sources. Can you help? (567)
I've never come across such pigments. In general it is difficult to produce such narrow absorption bands with the exception of some materials like rare earth metals. This is really a chemistry question and I am not sure who can best answer it. There is a department of colour chemistry at the University of Leeds. Perhaps someone there can point you in the right direction.   (Back to top)

As an Interior Design student I know that paint manufacturers, geologists, anthropologists, and color designers use the Munsell system of color notation. What other industries currently his system to code their color? Automobile industry? Textile Industry? (566)
I think you covered most of them. The system is also used in imaging (color reproduction) to help test and improve imaging systems. You might look at this paper I recently co-authored on Munsell and the system for American Scientist.   (Back to top)

Why do we recognize uniqueness only for four colors, blue, yellow, green, and red? Is there any color map of unique hues in a visual system? (565)
There seems to be a lot of physiological and psychophysical evidence supporting the special nature of the unique hues in the human visual system. I'd suggest a google scholar search to find lots of interesting references. "Why" is a difficult question, but it is probably related to the nature of the cone photopigment absorptivities and the transformation of them necessarily to maximally decorrelate the spectral signals in the natural world. It is hard to say there is an exact physiological locus for the unique hues, but there are certainly various types of opponent encodings that have been identified and there is certainly a map somewhere in the visual system because the response is such an easily accessible percept.   (Back to top)

How do we see metallic colors like gold and silver? (564)
We see metallic colors like gold and silver just like we see any other colors. It turns out the difference between metallics and other colors is a physical, not a perceptual, difference. The highlights (where the light sources are reflected) on metals take on the color of the material, while the highlights on other objects take on the color of the light source. That's due to the physical nature of how metals, as opposed to other materials, interact with light. There's a little bit more on this in another FAQ answer.   (Back to top)

Why is a red Popsicle red? (563)
Because, in our culture and language, "red" is the name chosen for the color perception generated by that Popsicle.   (Back to top)

What is the difference between value and chroma? If I add black or white to a color I am changing its value. How do I change its chroma? (562)
Value (or lightness) refers to the perceptual difference between white (high lightness or value) and black (low lightness). Chroma refers to the difference between a neutral gray (low chroma) and a color of the same lightness that is more colorful (like a vivid red ... a high chroma). Stimuli can, of course, vary in both dimensions at once when physical changes are made. If you add black or white to a color (regardless of what type of color mixing you are doing) you will certainly be changing the value, but you will also be changing chroma. If you want to just change chroma, you should mix the color with a gray of equal lightness.   (Back to top)

I measure pigments from bird egg shells with a spectrophotometer CM-2600d, should I work with 100%UV or 0%UV? What about pigments from bills and legs of birds? (561)
The reason for the UV selection in spectrophotometers is for the evaluation of fluorescence (some materials absorb the UV and re-emit that energy at visible wavelengths). I am not sure if the materials you are interested in are fluorescent, but measuring with the UV included and excluded will give you that answer. If the results are the same, then there is no fluorescence present and it won't matter which you select for future measurements. If the results differ, you will have to decide which is more relevant to your work. I would think that including the UV would make most sense since these materials are normally viewed in daylight, which has plenty of UV. But, again, it only matters if the materials are fluorescent ... otherwise the results will be the same either way.   (Back to top)

Out of blue, green or peach, which color is more likely to attract flies or insects and why? (560)
I don't know of detailed research myself. But I did a google search on the terms color, attraction, insects, and found quite a few pages of interest. This one (scroll down to the color part), suggests that the attractive colors vary by type of insect.   (Back to top)

What effect does light have on white paper: does it reflect or transmit? (559)
If the paper is a perfect white, then it would reflect 100% of the light incident on it and would reflect that light mostly in a diffuse (scattered in different directions) way. Real paper is not perfect and typically reflects something like 80% to 90% of the light that falls on it. The rest of the light is either absorbed or transmitted. If you can see light through the paper (i.e., it is not completely opaque), then you know it is transmitting some light.   (Back to top)

What is chromatic textile? What properties do this textile have? (558)
An achromatic color is a color devoid of hue (e.g., white, gray, black) and a chromatic color is a color with some appreciable amount of hue (e.g., different from gray). A chromatic textile would simply be a textile that has a hue.   (Back to top)

How do I compute the correlated color temperature of an Lab/Luv color coordinate? (557)
You can't compute correlated color temperature from CIELAB or CIELUV coordinates. Correlated color temperature is a metric associated with light sources and is computed from tristimulus values (XYZ) or chromaticity coordinates (xy, or u'v'). CIELAB and CIELUV are computed by normalizing out the light source so those coordinates no longer have the information you need to compute correlated color temperature.   (Back to top)

I'm trying to understand whether there is an optical/physical basis for this "chameleon effect" (the ability of the materials to blend with surrounding tooth structures to create naturally appearing restorations) and whether there may be way to measure it. (556)
This sounds like a fascinating color measurement question. I am not very familiar with the materials used or color measurement of teeth, but I can imagine a few things that might cause the "chameleon effect" you refer to. The first one would be scattering. It is possible that two materials have the same measured color and translucency, but one achieves it more through absorption and the other more through scattering. Whichever is more similar to the natural tooth material would blend in better under a variety of viewing conditions. Related to this could be index of refraction. The material with an index of refraction more closely matching the natural tooth would blend in better at the edges of the filling/repair. The third thing that comes to mind is metamerism. It is possible to produce the same color and translucency from different materials and end up with different spectral reflectance/transmittance properties. This could mean that a given material is a good match to the tooth under one viewing condition and a poor match under another. Difference materials could exhibit greater or lesser degrees of metamerism.   (Back to top)

I'm looking for the paint formulation for the official colors of West Virginia University. The Pantone colors are either: A) PMS 873 metallic gold and PMS 295 Navy Blue or B) PMS 124 Gold and PMS 286 Blue. Can you help? (555)
Since it sounds like the color matching system that the paint formulator has is not capable of matching Pantone colors directly (that would require the system developer to have licensed the Pantone system), the next best solution would be to use a Pantone book and have the formulator measure the two color patches on their spectrophotometer in order to formulate a match. If your formulator can't do that, go to another one. Most hardware stores have a spectrophotometer available to allow matching to customer samples. Go Mountaineers!!!   (Back to top)

In your opinion what pantone color best defines TEAL? (554)
The only opinion that matters is yours, or your customer's. The best thing to do is look through a set of Pantone samples and select the one that best represents teal to you. Color names are not generally used that consistently and there is usually no scientific way to pinpoint the best example.   (Back to top)

Can you help me calculate the color difference between my Macbeth Colorchecker and its image after capture and display on an LCD monitor? (553)
You need either an instrument to measure the XYZ values of the displayed chart (a colorimeter or spectroradiometer) or a characterization of the display that will allow you to convert the displayed RGB values to XYZ. You can then compute CIELAB values for both the original chart and the LCD display and from their calculate color differences using any of the recent CIE color difference equations. You might look in Berns' "Principles of Color Technology, 3rd Ed." for details on each of these steps.   (Back to top)

I would like to purchase a grey scale color variation kit for comparing the change in color wash for Denims and Textiles. Can you recommend a source for this kit? (552)
I believe the kit you are referring to is produced and sold by the AATCC and can be directly ordered through: this site. They also have other related products, so you might want to look around their website beyond the single item mentioned.   (Back to top)

Why does eye (iris) color appear to fade with old age? Is it because of the yellowing of the lens? (551)
I found a brief explanation online at wonderquest.com. Eye color is determined by the amount and distribution of melanin in the iris (melanin also gives our skin and hair its color). Apparently with age, the density (amount) of melanin can change in the iris resulting in the observed change in eye color. Similarly this can cause our hair to change color as we age. However, the perceived color of our iris does depend to a degree on having a dark area behind it and as we age the lens does yellow. That would make the area behind the iris less dark and therefore change the appearance of the iris. I would suspect that the changes in pigment density are far more important than changes in the lens, however. There are also other causes for changes in eye color that are mentioned in the linked column.   (Back to top)

Where can I find a tabulation of all pairs of distict spectral monochromatic lights that are perceived as achromatic? (550)
First of all, I assume you mean pairs of spectral lights that appear monochromatic when mixed together, in other words additive complementaries. I am not aware of any tabulated sets of complementary wavelengths. There are two reasons for this. One is that there is a large range of chromaticity coordinates that are perceived as achromatic due to chromatic adaptation in our visual system. Thus, the first step in this process is to decide which achromatic chromaticity is of interest. Once that decision is made, the complementary wavelengths are fairly easily computed from either the spectral chromaticities (a straight line through the achromatic point connects complementary wavelengths) or the color matching functions.   (Back to top)

At our paint-supply company we need to match a color to existing color on a clients' wall. Is there a portable instrument we can use to determine the required mix to match the exisitng paint? (549)
Yes. Most, if not all, of the instrument manufacturers make portable hand-held spectrophotometers that could make the necessary measurements. You would then need to match those measurements with your existing paints or use your current colorant formulation system to predict the paint recipe. If you currently have a non-portable system that does this job, then you should be able to use the colorimetric values measured on the portable system with your current software to predict a match. The instrument manufacturers should be able to help you put together an appropriate system.   (Back to top)

How can I know the tricolor chromaticity coordinate of a common CCD camera? (548)
A CCD camera does not have chromaticity coordinates. This is a common confusion between the analysis (measurement) of color and the synthesis (display) of color. Display primaries (and all displayed colors) have chromaticity coordinates. Camera signals do not have chromaticity coordinates until they are rendered to a display. With accurate analysis through characterization of the camera and accurate synthesis through characterization of the display it is sometimes possible to accurately recreate the chromaticity coordinates of the imaged scene on the display. The intermediate representation can be almost anything that preserves the data.   (Back to top)

How does color affect our vision? (547)
Color is our perception that results from vision. So you can't really say that color affects our vision since it is the product of our visual system. Color, in terms of the color of objects or light sources, can affect our visual performance. For example it is easier to read black text on white paper than it is to read yellow text on white paper. There are many ways that color affects visual performance. So many, in fact, that there is no way to give a short answer to this question.   (Back to top)

How do I calculate the chromaticity coordinates of a single wavelength of light? (546)
To compute the chromaticity coordinates for a monochromatic stimulus (a single wavelength, wl), simply read the values of the color matching functions (x-bar, y-bar, and z-bar) and do the following com