Enhanced compression of documents

• US 20020094127A1
• Filed: 01/16/2001
• Published: 07/18/2002
• Est. Priority Date: 01/16/2001
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Stepneski, David A., Prakash, Ravi, Mitchell, Joan L.
• Granted Patent: US 6,606,418 B2
• Time in Patent Office: Days
• US Class Current: 382/250
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/14 Coding unit complexity, e.g. amount of activity or edge presence estimation H04N19/146 takes precedence
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/18 the unit being a set of transform coefficients
• CPC Class Codes: H04N 19/40 using video transcoding, i.e. partial or full decoding of a coded input stream followed by re-encoding of the decoded output stream
• CPC Class Codes: H04N 19/46 Embedding additional information in the video signal during the compression process H04N19/517, H04N19/68, H04N19/70 take precedence
• CPC Class Codes: H04N 19/60 using transform coding
• CPC Class Codes: H04N 19/98 Adaptive-dynamic-range coding [ADRC]

Abstract

Increased and potentially extreme compression of documents is achieved by reducing/remapping the dynamic range of the document image possibly together with further image analysis and pre-processing and storing the document together with a substituted table of values chosen to restore or enhance the dynamic range of the document image. Increased or extreme compression is provided notwithstanding multiple image tones (e.g. colors or grey scale levels) even at low contrast within a document, such as a personal check. Such increased compression allows document images to be maintained in rapid-access memory for extended periods without increased storage costs.

Claims

1. A method of compressing data comprising steps of

selecting a first quantization table,

reducing the dynamic range of data, forming data of reduced dynamic range,

compressing said data of said reduced dynamic range with said first quantization table forming compressed data, and

storing or transmitting said compressed data together with a second quantization table representing a dynamic range other than said reduced dynamic range.

2. A method as recited in claim 1, including the further step of

determining a nominal dynamic range for data of interest.

3. A method as recited in claim 1, further including a step of remapping image values.

4. A method as recited in claim 1, wherein said step of reducing dynamic range of said data includes at least one of clipping and coring.

5. A method as recited in claim 1, wherein said step of remapping image valuesof said data includes at least one of clipping, coring and dynamic range reduction.

6. A method as recited in claim 1, including the further step of

decoding said compressed data using said second quantization table.

7. A method as recited in claim 6, wherein said decoding step is performed using a decoder implementing the JPEG standard.

8. An apparatus for compressing data comprising

means for selecting a first quantization table,

means for reducing the dynamic range of data,

forming data of reduced dynamic range,

means for compressing said data of said reduced dynamic range with said first quantization table forming compressed data, and

means for storing or transmitting said compressed data together with a second quantization table representing a dynamic range other than said reduced dynamic range.

9. An apparatus as recited in claim 8, further including

means for determining a nominal dynamic range for data of interest.

10. An apparatus as recited in claim 8, further including

means for remapping image values.

11. An apparatus as recited in claim 8, wherein said means for reducing dynamic range of said data includes means for at least one of clipping and coring.

12. An apparatus as recited in claim 8, wherein said means for remapping image valuesof said data includes means for at least one of clipping, coring and dynamic range reduction.

13. An apparatus as recited in claim 8, further including

means for decoding said compressed data using said second quantization table.

14. A method as recited in claim 13, wherein said means for decoding implements the JPEG standard.