METHOD AND APPARATUS FOR COMPRESSING COLOR OR GRAY SCALE DOCUMENTS

A technique for compressing a color or gray scale pixel map representing a document. The pixel map is decomposed into a three-plane representation, a reduced-resolution foreground plane, a reduced-resolution background plane, and a high-resolution binary selector plane. The foreground plane contains the color or gray scale information of foreground items such as text. The background plane contains the color or gray scale information for the "background" of the page and the continuous tone pictures that are contained on the page. The selector plane stores information for selecting from either the foreground plane or background plane during decompression. Each of the respective planes is compressed using a compression technique optimal for the corresponding data type. Also described is a method for decompressing documents compressed into the three plane representation at arbitrary resolutions.