Patent ID: 7092571

Claim:
A method of determining variations of a test image with respect to a reference image, the method comprising: a) storing the reference image in a memory, wherein the reference image comprises a plurality of pixels, wherein each of the pixels comprises at least one value; b) storing the test image in a memory, wherein the test image comprises a plurality of pixels, wherein each of the pixels comprises at least one value; c) specifying one or more regions in the test image and corresponding regions in the reference image; d) specifying a plurality of sub-regions for each test image region and a plurality of corresponding sub-regions in the corresponding reference image region; e) calculating an average of the values of the pixels in each of the sub-regions in a test image region and the corresponding reference image region; f) calculating differences between the average values for respective corresponding sub-regions in the test image region and the corresponding reference image region; g) comparing the absolute difference calculated for a test image sub-region to a specified maximum difference, and wherein, if the absolute difference is greater than the maximum difference, searching for a shifted sub-region of the reference image region that has an absolute difference with the test image sub-region that is less than the maximum difference and which has an absolute shift less than a specified maximum shift; and h) generating a test result indicative of the variations of the test image with respect to the reference image in the specified regions, wherein generating a test result for a region comprises generating a test result of FAIL if any sub-region in the test image region has an absolute difference greater than the maximum difference and there is no shifted sub-region that has an absolute spatial shift less than a specified maximum shift and an absolute difference less than the maximum difference.