A method and apparatus for compressing a mixed raster content image that represents a color or gray scale a document is disclosed. The pixel map is decomposed into a three-plane representation--a reduced-resolution "upper" plane, a reduced-resolution "lower" plane, and a high-resolution binary selector...http://www.google.com/patents/US6334001?utm_source=gb-gplus-sharePatent US6334001 - Iterative smoothing technique for pre-processing mixed raster content planes to improve the quality of a decompressed image and increase document compression ratios
