Method for compressing digital documents with control of image quality subject to multiple compression rate constraints

• US 20020097917A1
• Filed: 12/04/2000
• Published: 07/25/2002
• Est. Priority Date: 05/12/2000
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: DʼOrtenzio, Remo J., Sweet, James M., Nelson, William E.
• Granted Patent: US 6,804,401 B2
• Time in Patent Office: Days
• US Class Current: 382/239
• CPC Class Codes: G06T 9/00 Image coding bandwidth or redundancy reduction for static pictures H04N1/41; coding or decoding of static colour picture signals H04N1/64; methods or arrangements for coding, decoding, compressing or decompressing digital video signals H04N19/00
• CPC Class Codes: H04N 1/3333 during transmission, input or output of the picture signal; within a single document or page
• CPC Class Codes: H04N 1/41 Bandwidth or redundancy reduction by scanning H04N1/17 ; methods or arrangements for coding, decoding, compressing or decompressing digital video signals H04N19/00
• CPC Class Codes: H04N 2201/33357 Compression mode

Abstract

A method for digital image compression of a raster image is disclosed which uses different compression methods for selected parts of the image and which dynamically adjusts compression and segmentation parameters to control tradeoff of image quality and compression. The image is encoded into a single data stream for efficient handling by disk, memory and I/O systems. This system provides a stable feedback loop that manages to a fine granularity (typically 8×8 pixel blocks) the compression of image data so as to be compliant with a plurality of compression constraints; the management of an incremental bias toward more aggressive compression that selectively applies the more aggressive compression methods to blocks that are the most tolerant with respect to visible artifacts; and the adjustable segmentation and compression parameters used to control the image compression.

Claims

1. A method of compressing a received document, comprising:

receiving a documents containing unknown combinations of a plural data types;

determining a required compression amount for the document,

compressing portions of the document with a compression method selected to meet a local compression constraint;

comparing actual compression with said local compression constraint

iteratively compressing portions of the document with progressively more aggressive compression techniques to meet said local compression constraint.

2. The method described in claim 1, and including

comparing actual compression of the document with a global compression constraints;

iteratively compressing said document with progressively more aggressive compression techniques to meet said global compression constraint.

3. A compression system comprising a document input, receiving documents containing unknown combinations of a plural data types

plural document compression systems, providing lossy compression and lossless compression

a compression comparison arrangement, comparing compressed document information with compression constraints to determine whether an amount of compression applied to a document meets compression constraint requirements;

a feedback arrangement, controlling selection of said plural document compression devices to increase compression applied to documents to meet compression restraint requirements

an iterative compression processor, iteratively processing documents, responsive to said feedback arrangement.