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Picture Elements Incorporated

D Michael Ott

Frederick Crowhurst

Stephen D Williams

Cindy D Ott

A method for processing a digital image of a document to provide one or more bitonal digital copies of selected image quality that are optimized for specific purposes. The method is suited for use with such documents as bank checks and commercial forms that have printed or handwritten textual characters overlaid on potentially obscuring backgrounds. The method may provide a clean bitonal digital copy with reduced background optimized for use in optical character recognition or an archival copy with meaningful background retained that is optimized for archiving the original document. A set of bitonal copies of the digital image of a document is derived covering a range of contrast sensitivities. The copies are compared and a numerical measure is provided representing the amount of change in going from one copy to the next. The collection of such numerical measures defines a numerical sequence representing variations in the digital image as the contrast sensitivity is monotonically varied. The image-variation sequence is automatically analyzed to find the region or regions of rapid dropoff, generally signifying that certain unwanted or wanted features of the image are dropping out, and to find regions of more gradual changes. Optimizing values of the contrast sensitivities are selected to fall in select positions with respect to the peak or peaks and tails that are found in the sequence. The optimizing contrast sensitivities are used to generate one or more optimized bitonal digital copies such as a clean image or an archival image.

Automatic bitonal image optimization

A method for improved readability of digitally captured document images that include printed or handwritten textual material overlaid on background graphics. Text in the document is generally composed at least in part of strokes characterized by pairs of edges in close proximity to one another. The digital image comprises an array of pixels representing at least a portion of the document. The edges in the pixel array are first identified and then grown by an effective amount so as to cause pairs of edges characterizing each stroke substantially to merge. The grown edges are then shrunk by an effective amount so as to cause non-stroke edges to be substantially eliminated without eliminating the merged stroke edges. A binarized representation of the merged stroke edges is then provided using an algorithm that is adapted to give a good representation of edge images, and a binarized representation of non-stroke regions of the pixel array is provided using a different algorithm especially adapted to represent the non-stroke regions. A document image with reconstructed textual matter may also be combined with a representation of the background graphics in which the overall contrast of the background graphics has been reduced. This may be achieved, for example, by scaling back the contrast of the captured digital image by a fixed percentage or by a variable amount prescribed by a formula, and then subjecting the scaled-back image data to a process such as a digital half-tone process providing a good binarized representation of the reduced-contrast image.

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Oakland, CA, United States of America

D Michael Ott