digital image restoration
The methods used to clarify characters on the Dead Sea Scrolls combine electronic sensors with digital image processing to improve the legibility of ancient texts using multispectral image analysis. Several digital images of a scroll are recorded in different wavelengths of light and enhanced using specialized imaging software. Together, these methods have revealed valuable new information that has not been seen for over two thousand years.

The images are recorded by an electronic camera, which converts the light intensity in each small section of the image to an electrical signal that may be "read" by a computer. The individual segments of the image are called "picture elements" (usually abbreviated to "pixels" or "pels"). Several types of electronic cameras are now available, but that used is one of the most common class known as "charge coupled device cameras," or "CCD cameras." CCD technology is now used in consumer digital cameras and videotape camcorders available from many manufacturers.

The particular camera used in our experiments is a specially designed instrument, made available to use by Eastman Kodak Company. It is sensitive over an unusually wide range of wavelengths. To utilize different wavelength ranges, colored glass "filters" are placed over the camera lens before making the exposure. To record what the eye sees, red, green and blue filters are used. The wavelength of light is the physical distance between the oscillation of the electromagnetic wave, and usually is measured in "nanometers;" one nanometer is 1/1000 of 1 millionth of a meter. Humans can see wavelengths in the range of 400 nanometers (4/10 of a millionth of a meter) for blue light, up to 700 nanometeres (7/10 of a millionth of a meter) for red light. This CCD camera is sensitive to light with wavelengths shorter than the eye can see: down to 200 nanometers in the "ultraviolet" region of the spectrum. The camera is also sensitive to wavelengths longer than the eye can see: out to 1200 nanometers in the "infrared" spectrum.

Ancient documents, such as the Dead Sea Scrolls, often have been degraded by centuries of exposure to the elements. The degraded areas of a scroll exhibit very poor contrast to the eye between the printed characters and the parchment surface, which is the animal skin analogue of paper. The use of images seen in different wavelengths provides information that the eye cannot see, allowing the clarity of the characters to be greatly enhanced. We found that the contrast differences are most apparent in the infrared images on the parchment documents that we have analyzed.

After the images have been gathered, they are processed in a digital computer. In our work, we use the image processing system developed by Xerox Corporation at their Digital Imaging Technology Center in Webster, New York. Software programs are used that allow images to be analyzed, combined in different ways (added, subtracted, multiplied, divided, recolorized, etc.), displayed and printed. Together, the multispectral images and image processing technology have revealed valuable new information to scholars of these ancient texts.

Inside the Lab

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Methodology of Digital Image Restoration

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