Characterization of the Effects of Spatial Translations on JPEG-compressed Images

Keith Jacoby

Appendix A: MatLab Routines

MatLab 8x8 Blocking DCT routine

%  Keith Jacoby----Senior Research Project----4/10/1998

%  

%  Block DCT:  This little beauty performs a block DCT on an 8-bit

%  grayscale image, and outputs the DCT image as a TIFF.  In addition,

%  the blocks' DC coefficients are set to zero to make the DCT images

%  easier to interpret.  Finally, the DCT image is block-ensemble-

%  averaged into 1 8x8 block that is an average of all the 8x8 DCT 

%  blocks in the entire DCT image. I LOVE MATLAB!!!  :)

%  It's really fun...

%

IMG1=imread('sft8radgrad.tiff','tiff');

figure(1)

imshow(IMG1,256)

IMG2=blkproc(IMG1,[8 8],'dct2(x)');

figure(2)

imshow(IMG2,256)

for i = 1:8:256,

	for j = 1:8:256,

		IMG2(i,j) = 0.0;

	end

end

IMG2min=min(min(IMG2));

IMG2max=max(max(IMG2));

IMG3=mat2gray(IMG2,[IMG2min IMG2max]);

imwrite(IMG3,'sft8dct.tiff','tiff');

%

%  Ensemble Averaging of 8x8 blocks

%

SUM8x8(8,8)=0;

for C = 1:8,

	for R = 1:8,

		for i = R:8:249,

			for j = C:8:249,

			SUM8x8(R,C)=SUM8x8(R,C)+IMG2(i,j);

		    end

	    end

    end

end

SUM8x8AVE=SUM8x8/1024;

SUM8x8AVE

MatLab Correlation routine

%     Keith Jacoby  Senior Research  4/13/98

%

%	This tiny routine performs a correlation on two images

%	and returns a value R = correlation coefficient

%

IMG1=IMREAD('1-pix_shift_close40.tif','tiff');

figure(1)

imshow(IMG1,256)

IMG2=IMREAD('close40.tif','tiff');

figure(2)

imshow(IMG2,256)

R=CORR2(IMG1,IMG2)

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