Method and apparatus for compressing color or gray scale documents
DCFirst Claim
1. A method for compressing a pixel map representation of a document, said pixel map representation having a resolution of X spots per inch, said method comprising the steps of:
- a) creating a foreground pixel map from said pixel map representation of a document, said foreground pixel map having a resolution less than X spots per inch and containing color information for foreground elements of said document;
b) creating a background pixel map from said pixel map representation of a document, said background pixel map having a resolution less than X spots per inch and containing image information for image portions and color information for non-foreground portions of said document;
c) creating a selector map from said pixel map representation of a document, said selector map for selecting between pixels in said foreground pixel map and said background pixel map when decompressing said compressed pixel map representation of said document;
d) compressing and storing each of said foreground pixel map and said background pixel map using a compression technique suitable for compressing images; and
e) compressing said selector map using a technique suitable for compressing bitmaps.
10 Assignments
Litigations
0 Petitions
Accused Products
Abstract
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.
297 Citations
20 Claims
-
1. A method for compressing a pixel map representation of a document, said pixel map representation having a resolution of X spots per inch, said method comprising the steps of:
-
a) creating a foreground pixel map from said pixel map representation of a document, said foreground pixel map having a resolution less than X spots per inch and containing color information for foreground elements of said document; b) creating a background pixel map from said pixel map representation of a document, said background pixel map having a resolution less than X spots per inch and containing image information for image portions and color information for non-foreground portions of said document; c) creating a selector map from said pixel map representation of a document, said selector map for selecting between pixels in said foreground pixel map and said background pixel map when decompressing said compressed pixel map representation of said document; d) compressing and storing each of said foreground pixel map and said background pixel map using a compression technique suitable for compressing images; and e) compressing said selector map using a technique suitable for compressing bitmaps. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
-
-
11. A system for processing with pixel map representations of documents comprising:
-
input means for receiving a pixel map representation of a document; and compression means for compressing said pixel map representation of a document, said compression means comprising; decomposing means for decomposing said pixel map representation of a document into a foreground pixel map containing color information for foreground elements of said document, a background pixel map containing image information for image portions and color information for non-text portions of said document, and a selector map for selecting between said foreground pixel map and said background pixel map; and means for applying a suitable compression technique to each of said foreground pixel map, background pixel map and said selector map. - View Dependent Claims (12, 13, 14, 15, 16)
-
-
17. A program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine to perform method steps for compressing a document image, said method steps comprising:
-
a) receiving a pixel map representation of a document; b) creating a thresholded bitmap from said pixel map representation of a document, said thresholded bitmap having a resolution greater than X spots per inch; c) creating a foreground pixel map from said thresholded bitmap, said foreground pixel map having a resolution less than X spots per inch and containing color information for foreground elements of said document; d) creating a background pixel map from said pixel map representation of a document, said background pixel map having a resolution less than X spots per inch and containing image information for image portions and color information for non-text portions of said document; e) creating a selector map from said pixel map representation of a document, said selector map for selecting between pixels in said foreground pixel map and said background pixel map when decompressing said compressed pixel map representation of said document; f) compressing and storing each of said foreground pixel map and said background pixel map using a compression technique suitable for compressing images; and g) compressing said selector map using a pattern matching compression technique. - View Dependent Claims (18)
-
-
19. A method for decompressing a compressed document image comprising the steps of:
-
a) receiving a compressed document image representation having an original resolution X, said compressed document image representation comprising a compressed foreground pixel map containing color information for foreground elements of said document, a compressed background pixel map containing image information for image portions and color information for non-text portions of said document, and a compressed selector map for selecting between said foreground pixel map and said background pixel map; b) decompressing each of said compressed foreground pixel map, compressed background pixel map and said compressed selector map; c) determining a decompression resolution; d) if said decompression resolution is greater than or equal to X, creating said decompressed pixel map by using said selector map to choose between pixel values in said foreground pixel map and pixel values in said background pixel map for said decompressed bitmap; and e) if said decompressed resolution is less than X, scaling the decompressed pixel values based on the contribution of corresponding pixel values from said foreground pixel map and said background pixel map. - View Dependent Claims (20)
-
Specification