System and method for directed acuity segmentation resolution compression and decompression

• US 7,123,771 B2
• Filed: 12/26/2001
• Issued: 10/17/2006
• Est. Priority Date: 12/23/1998
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Curry, Douglas N.
• Primary Examiner(s): Do, Anh Hong
• Application Number:
  US10/025,671
• Publication Number:
  US 20020097430A1
• Time in Patent Office: 1,756 Days
• Field of Search: 382/239, 382/233, 382/237, 382/236, 382/254, 382/248, 382/266, 382/298, 382/170, 382/224, 382/232, 382/301, 382/269, 382/241, 382/246, 382/244, 382/313, 348/607, 345/503, 712/32, 700/8, 358/1.9, 235/462.18, 375/240
• US Class Current: 382/233
• 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 1/411 for the transmission or storage or reproduction of two-tone pictures, e.g. black and white pictures

Abstract

A compression and decompression system and process for optimally compressing and decompressing multibit per pixel image regions based on the type of data contained in the image region, e.g., whether the image region contains continuous tone data, including data to be halftoned, or non-continuous tone data, including antialiased text and lineart data. Segmented bytemap data blocks are processed to provide both low spatial resolution continuous tone data and high spatial resolution non-continuous tone data. However, the high spatial resolution non-continuous tone data is generated by quantizing and packing the high resolution bytes across an edge and discarding the high resolution bytes along the edge, i.e., the multibit data is discarded only in directions parallel to the edges of marks to be rendered in the image data. Additional information indicating the directions of the edges in the image data are stored to aid in decompression. Subsequently, during decompression, the non-continuous tone data is decompressed into a high spatial resolution bytemap by unpacking the high resolution across the edges and inferring the high resolution along the edges. The low spatial resolution continuous tone data are processed to provide a low spatial resolution continuous tone data bytemap. As a result of this compression and decompression method, the amount of memory necessary to store the non-continuous tone data is reduced to a quarter of the memory necessary to store a conventional high spatial resolution bytemap.

Claims

1. A method for decompressing image data, that is compressed by discarding pixels along a direction parallel to an edge while maintaining pixels along a direction perpendicular to the edge, representing a plurality of pixels and represented by a plurality of bitwords, each pixel corresponding to a separate bitword, the process comprising:

decompressing data from a compressed-data-bitword to provide data indicative of a plurality of explicit pixels; and

synthesizing data from the data indicative of the plurality of explicit pixels to provide data corresponding to at least one synthesized pixel, the at least one synthesized pixel representing at least one discarded pixel.

2. The method of claim 1, wherein decompressing a quantity of non-continuous tone data is increased to approximately four times of a quantity of uncompressed non-continuous tone data present in a plurality of bitwords representing a plurality of pixels.

3. The method of claim 1, wherein, during decompression, non-continuous tone data with a high spatial resolution in one dimension is decompressed into a high spatial resolution bitword-map with reference to information indicating the direction of the edge within the image data.

4. The method of claim 1, wherein, decompressing the data from the compressed bitword for a single data pixel comprises:

identifying a bit word as continuous tone data; and

decompressing continuous tone data to provide image data for a single pixel at a higher spatial resolution corresponding to a plurality of pixels.

5. The method of claim 4, wherein, decompressing the data from the compressed bitword for a single data pixel comprises:

synthesizing bitwords of information corresponding to discarded non-continuous tone data; and

copying the single pixel to provide the image for the surrounding pixels.

6. The method of claim 1, wherein each of the bitwords are bytes.

7. The method of claim 6, wherein, for each bitword, synthesizing the data is performed in either a fastscan direction or a slowscan direction based on a direction bit contained in that bitword.

8. The method of claim 7, wherein, synthesizing the data comprises determining which pixel positions are to be synthesized during decompression based on the direction bit.

9. A method for decompressing image data, that is compressed by discarding pixels along a direction parallel to an edge, representing a plurality of pixels and represented by a plurality of bitwords, each pixel corresponding to a separate bitword, the process comprising:

decompressing data from a compressed-data-bitword to provide data indicative of a plurality of explicit pixels; and

synthesizing data from the data indicative of the plurality of explicit pixels to provide data corresponding to at least one synthesized pixel, the at least one synthesized pixel representing at least one discarded pixel,

wherein each of the bitwords are bytes;

wherein decompressing the data from the compressed bitword comprises;

referencing a segmentation bit of the bitword to determine whether the bitword contains non-continuous tone data;

referencing a direction bit to determine whether the direction of the edge located in spaced relationship to a first and a second pixel;

referencing a three-bit value indicative of the first pixel; and

referencing a three-bit value indicative of the second pixel.

10. A method for decompressing image data, that is compressed by discarding pixels along a direction parallel to an edge, representing a plurality of pixels and represented by a plurality of bitwords, each pixel corresponding to a separate bitword, the process comprising:

decompressing data from a compressed-data-bitword to provide data indicative of a plurality of explicit pixels; and

synthesizing data from the data indicative of the plurality of explicit pixels to provide data corresponding to at least one synthesized pixel, the at least one synthesized pixel representing at least one discarded pixel;

wherein each of the bitwords are bytes;

wherein for each bitword, synthesizing the data is performed in either a fastscan direction or a slowscan direction based on a direction bit contained in that bitword;

wherein synthesizing the data comprises;

determining which pixel positions are to be synthesized during decompression based on the direction bit;

rendering from each bitword twice as many pixels in a direction perpendicular to an edge indicated by the direction bit of that bitword.

11. A method for decompressing image data, that is compressed by discarding pixels along a direction parallel to an edge, representing a plurality of pixels and represented by a plurality of bitwords, each pixel corresponding to a separate bitword, the process comprising:

decompressing data from a compressed-data-bitword to provide data indicative of a plurality of explicit pixels; and

synthesizing data from the data indicative of the plurality of explicit pixels to provide data corresponding to at least one synthesized pixel, the at least one synthesized pixel representing at least one discarded pixel;

wherein each of the bitwords are bytes;

wherein for each bitword, synthesizing the data is performed in either a fastscan direction or a slowscan direction based on a direction bit contained in that bitword;

wherein synthesizing the data comprises;

determining which pixel positions are to be synthesized during decompression based on the direction bit;

when the direction bit indicates a vertical edge, using the three-bit value associated with the first pixel and the three-bit value associated with the second pixel in the compressed-data-bitword to determine slope in the fast scan direction to render the vertical edge.

12. A method for decompressing image data, that is compressed by discarding pixels along a direction parallel to an edge, representing a plurality of pixels and represented by a plurality of bitwords, each pixel corresponding to a separate bitword, the process comprising:

decompressing data from a compressed-data-bitword to provide data indicative of a plurality of explicit pixels; and

synthesizing data from the data indicative of the plurality of explicit pixels to provide data corresponding to at least one synthesized pixel, the at least one synthesized pixel representing at least one discarded pixel;

wherein each of the bitwords are bytes;

wherein for each bitword, synthesizing the data is performed in either a fastscan direction or a slowscan direction based on a direction bit contained in that bitword;

wherein synthesizing the data comprises;

determining which pixel positions are to be synthesized during decompression based on the direction bit;

when the direction bit indicates a horizontal edge, using the three-bit value associated with the first pixel and the three-bit value associated with the second pixel in the byte of compressed data to determine slope in the slow scan direction to render the horizontal edge.

13. A method for decompressing compressed image data that is compressed by discarding pixels along a direction parallel to an edge while maintaining pixels along a direction perpendicular to the edge, the method comprising:

decompressing a single byte of compressed data to produce four pixels of non-continuous tone data.

14. The method of claim 13, further comprising, transmitting the byte of data to a print engine where the step of decompressing is performed, the step of decompressing including extracting data necessary to render two non-continuous tone data pixels and fabricating two more non-continuous tone data pixels in a low-spatial resolution direction based on a set of values of the extracted data.

15. The method of claim 13, wherein the four pixels represent a two-by-two pixel array.

16. A decompression system for decompressing image data, the image data containing non-continuous tone data and continuous tone data, the non-continuous tone data compressed by discarding pixels along a direction parallel to an edge while maintaining pixels along a direction perpendicular to the edge, the system comprising:

a decompressor that decompresses a data bitword-map to provide high spatial resolution data containing non-continuous tone data using extra resolution in a direction substantially perpendicular to an edge of marks, and that decompresses the data bitword-map to provide low spatial resolution continuous tone data.

17. The decompression system of claim 16, further comprising an image forming device, wherein the decompression system is incorporated in the image forming device.

18. The decompression system of claim 17, wherein the image forming device is one of at least a facsimile machine, a laser printer, an inkjet printer, a digital copier or a full-width-print bar printer.