1. 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; and identifying as candidate pixels the image pixels having a gradient value exceeding a gradient threshold, the candidate pixels comprising the candidate defect.