Dust, scratch detection for image scanner involves scanning shadows of defect with photosensor arrangements arranged so shadow lengths differ, detecting different length shadows

摘要

The method involves scanning a first shadow produced by the defect using a first photosensor (108), scanning a second shadow produced by the defect using a second photosensor (110) arranged so that the length of the first shadow is different from the second, detecting the two shadows from data from the detected shadows and determining that a defect is present if shadows of different lengths are detected.