ImageDifference
ImageDifference[image1, image2] gives an image where each pixel is the absolute difference of the corresponding pixels in image1 and image2.
Examples
Compute difference between images:
img1 = ExampleData[{"TestImage", "Lena"}];
img2 = GaussianFilter[img1, 5];
ImageDifference[img1, img2]Detect changes:
ImageDifference[img1, ColorNegate[img1]]Something isn't working? Report an issue.
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