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Abstract

A digital image preprocessing method for eliminating background patterns and scenes from digitized gray level document image data. The method accepts multi-gray level image data as input and produces a gray level output image containing a 'white' background. Document image backgrounds are eliminated (or suppressed) by computing a separate (and typically different) threshold value for each gray level pixel of the original document image. Input image pixels whose gray level is greater (brighter) than the threshold value are assumed to be background picture data and are modified to be 'white' pixels in the output image. The pixel threshold value is determined dynamically pixel-to-pixel based on gray level pixel data observed within the input image. Additionally, the pixel threshold can be automatically controlled to insure retention of written and/or printed information present in the input image. Threshold control is accomplished by specifying a print contrast signal (PCS) parameter to the image preprocessing method. Documents which might use this preprocessing technique include, but are not limited to, bank checks, remittance documents, charge card slips, deposit slips and similar type financial documents.

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First Claim