Patent ID: 8837807

Claim:
Method for inspecting flat objects, especially wafers, with an object surface, the method comprising the steps of: (a) scanning a digital image with a plurality of image points of said object surface with color- or grey values for each of said image points; (b) detecting defects on said object surface by comparing said scanned digital image to a digital reference image; (c) defining and selecting corresponding portions in said scanned digital image and in the digital reference image; (d) determining a representative color- or grey value for each of said selected portions; (e) calculating a compare value from said representative color- or grey value of said scanned digital image of a portion and a representative color- or grey value of said digital reference image of the same portion; (f) correcting each image point of said scanned digital image with a correction value determined from said compare value of step (e); and (g) wherein the size of said portions is selected such that said compare values of adjacent portions vary less with one from the other than a selected threshold value.