System and method for enhancing document images

摘要

A system and method for enhancing digital images containing both text and pictorial content ("mixed document images") utilizes an estimated illumination surface for a given digital image to correct the undesirable effect of non-uniform illumination. The estimated illumination surface is based on the luminance values of the edge pixels of the given image that are on the dark side of text edges. In an alternative embodiment, the luminance values of the edge pixels that are on the lighter side of the detected text edges are used to generate the estimated illumination surface. The estimated illumination surface is applied to the digital image to compensate for illumination variations in the image due to non-uniform illumination. In addition to non-uniform illumination correction, the system and method enhances the mixed document images by sharpening and/or darkening edges of text contained in the images.