T. Kanungo et al., NONLINEAR GLOBAL AND LOCAL DOCUMENT DEGRADATION MODELS, International journal of imaging systems and technology, 5(3), 1994, pp. 220-230
Two sources of document degradation are modeled: 1) perspective distor
tion that occurs while photocopying or scanning thick, bound documents
; and 2) degradation due to perturbation in the optical scanning and d
igitization process: speckle, blurr, jitter, and threshold. Perspectiv
e distortion is modeled by studying the underlying perspective geometr
y of the optical system of photocopiers and scanners. An illumination
model is described to account for the nonlinear intensity change occur
ring across a page in a perspective-distorted document. The optical di
stortion process is modeled morphologically. First, a distance transfo
rm on the foreground is performed; this is followed by a random invers
ion of binary pixels in which the probability of flip is a function of
the distance of the pixel to the boundary of the foreground. Correlat
ing the flipped pixels is modeled by a morphological closing operation
. (C) 1995 John Wiley & Sons, Inc.