Patent ID: 8644587

Claim:
A method of detecting optical defects in a transparency, comprising the steps of: providing a digital image of the transparency, the digital image including a plurality of image pixels each having a grayscale intensity; detecting at least one candidate defect by performing the following: determining a grayscale intensity of each one of the image pixels; calculating an intensity gradient across adjacent pairs of the image pixels; assigning to each image pixel a gradient value comprising a maximum of the absolute value of the intensity gradients associated with the image pixel; constructing a gradient image comprising the gradient values assigned to corresponding ones of the image pixels; identifying as candidate pixels the image pixels having a gradient value exceeding a gradient threshold, the candidate pixels comprising the candidate defect; comparing a quantity of the candidate pixels to a pixel quantity threshold to identify the candidate defect as an optical defect; and transforming, using a fixed coordinate transformation, a two-dimensional location of the optical defect on the digital image into a three-dimensional location on the transparency.