Global and local document degradation models

Two sources of document degradation are modeled { i) perspective distortion that occurs while photocopying or scanning thick, bound documents, and ii) degradation due to perturbation in the optical scanning and digitization process: speckle, blurr, jitter, threshold. Perspective distortion is modeled by studying the underlying perspective geometry of the optical system of photocopiers and scanners. An illumination model is described to account for the non-linear intensity change occuring across a page in a perspective-distorted document. The optical distortion process is modeled morphlogically. First a distance transform on the foreground is performed and followed by a random inversion of binary pixels where the probability of ip is a function of the distance of the pixel to the boundary of the foreground. Correlating the ipped pixels is modeled by a morphological closing operation.