Patent ID: 7336815

Claim:
An image defect inspection method which detects a gray level difference between corresponding portions of two images, compares said detected gray level difference with a threshold value, and judges one or the other of said portions to be defective if said gray level difference is larger than said threshold value, wherein a cumulative frequency of said gray level difference between said two images is computed, a converted cumulative frequency is computed by converting said cumulative frequency so that said cumulative frequency shows a linear relationship to said gray level difference when said gray level difference is assumed to have a distribution that obeys a prescribed type of distribution, an approximate straight line is computed by approximating said converted cumulative frequency by a straight line in each of two regions, one where said gray level difference is positive and the other where said gray level difference is negative, when the difference between the slopes of said approximate straight lines is larger than a predetermined value, the approximate straight line having the smaller slope is corrected in such a manner said slope increases, based on said approximate straight line, said threshold value is determined from a prescribed cumulative frequency value in accordance with a prescribed calculation method, and said comparison is performed using said determined threshold value.