United States Patent   Patent Number: 5,778,092
MacLeod et al.  Date of Patent: Jul. 7, 1998
 METHOD AND APPARATUS FOR
COMPRESSING COLOR OR GRAY SCALE
 Inventors: Peter S. MacLeod, Oakland; Luc
Vincent. Palo Alto; Xianing Zhu. San
Jose, all of Calif.
 Assignee: Xerox Corporation. Stamford, Conn.
 Appl. No.: 770391
 Filed: Dec. 20,1996
 Int. CI.6 H04N 1/64
 U.S. CI 382/176; 382/284; 358/534;
 Field of Search 358/534. 536.
358/540. 429, 450. 451. 455. 456. 459, 462. 464, 539; 382/176. 284. 291, 292.
298. 299; H04N 1/64
 References Cited
U.S. PATENT DOCUMENTS 5,615^81 3/1997 Yamaguchi 382/299
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.
20 Claims, 25 Drawing Sheets