Software system for minimizing image defects in a hard-copy input scanner

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.