%sample data
firstImage = imread('cameraman.tif');
secondImage = imresize( rgb2gray( imread('flamingos.jpg') ), size(firstImage));
%assuming grayscale images
imgdiff = double(firstImage) - double(secondImage);
n0p = sign(imgdiff); %-1 for negative, 0 for equal, 1 for positive
%add 2 to n0p to get a 1-based index
cmap = [1 0 0; 0 0 0; 0 0 1]; %red, black, blue
diffImg = reshape(cmap(n0p+2,:), size(imgdiff,1), size(imgdiff,2), 3);
%show it off
subplot(3,1,1)
imshow(firstImage);
title('cameraman')
subplot(3,1,2)
imshow(secondImage);
title('flamingos')
subplot(3,1,3)
imshow(diffImg);
title('color difference image')
