1. A document image processing system, comprising: means for photoelectrically dither processing, by binarizing error diffusion, a multivalue document image having a shading background to obtain a binary dither processed image in which image density is expressed in terms of horizontal line width and density; means for reconstructing multivalue image data from the binary dither processed image to obtain reconstructed multivalue image data; means for removing a shading background from the reconstructed multivalue image data to produce deshaded reconstructed binary image data; and means for compression encoding the deshaded reconstructed binary image data.