Contrast Enhancement of Mail Piece Images

A new approach to contrast enhancement of mail piece images is presented. The contrast enhancement is used as a preprocessing step in the real-time address block location (RT-ABL) system. The RT-ABL system processes a stream of mail piece images and locates destination address blocks. Most of the mail pieces (classified into letters) show high contrast between background and foreground. As an extreme case, however, the seasonal greeting cards usually use colored envelopes which results in reduced contrast of the image, leading to background degradation. Another extreme case is the foreground degradation due to the light foreground strokes. These extreme cases can affect the selection of useful information from an image, thus affecting the decision, and decreasing the performance of the system. In this paper, a non-linear mapping M(A,u,P), where A is the local average, (T is the local standard deviation and P is the center pixel over a 9 x 9 window, is used to enhance the contrast of both the background and foreground degradations without affecting the nondegraded images. This approach provides local enhancement which adapts __ J~LIQ~aLf~_atJlr.es_._~_or_der_to_J3impli£y--the computation-of .A .. and-g-,-dynamiG-p.rogram.m:ing-techuiq-tle--is--used~· Implementation details, performance and the results on test images are prese,.p.ted in this paper.