In a document handler associated with an input scanner, such as for a
digital copier or facsimile machine, an image-bearing sheet is moved over
a relatively narrow window, through which the image is recorded by a
photosensitive chip. When a spot of dirt attaches to the window, a streak
results in the image data. This streaking problem is addressed by
detecting image data consistent with such a streak, and applying a
suitable correction algorithm to the image data. The suitable algorithm is
chosen based on the thickness of the streak and the nature of the image
data.