System and method for directed acuity segmentation resolution compression and decompression

• US 6,771,827 B1
• Filed: 12/23/1998
• Issued: 08/03/2004
• 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:
  US09/219,850
• Time in Patent Office: 2,050 Days
• Field of Search: 382/232, 382/239, 382/266, 382/218, 382/245, 382/236, 382/237, 382/238, 382/233, 382/240, 382/246, 382/247, 382/248, 382/250, 358/448, 358/426, 358/429, 348/400.1
• US Class Current: 382/239
• 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 process for compressing and decompressing image data representing a plurality of pixels and represented by a plurality of bitwords, each pixel corresponding to a separate bitword, the process comprising:

discarding a quantity of bitwords along a direction of an edge while keeping bitwords across the direction of the edge;

compressing data indicative of a plurality of explicit pixels remaining after the discarding step into a single compressed-data-bitword;

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

synthesizing data from the decompressed-data-bitword to provide data corresponding to a synthesized pixel.

2. The process of claim 1, wherein the step of compressing includes reducing a quantity of bits necessary to represent non-continuous tone data.

3. The process of claim 1, wherein the discarded quantity of bitwords is half of the bitwords in the plurality of bitwords.

4. The process of claim 1, wherein the quantity of discarded bitwords includes half of the bitwords corresponding to non-continuous tone data in the plurality of bitwords.

5. The process of claim 1, wherein the quantity of discarded bitwords includes three-quarters of the bytes corresponding to continuous tone data in the plurality of bitwords.

6. The process of claim 1, wherein the step of compressing data indicative of the plurality of explicit pixels remaining after the discarding step into the single compressed-data-bitword is performed on pixels that contain non-continuous tone data.

7. The process of claim 1, wherein the step of compressing includes maintaining any bitwords indicative of continuous tone data so that each pixel of continuous tone data corresponds to a separate bitword of the plurality of bitwords.

8. The process of claim 1, wherein discarding the quantity of bitwords produces low spatial resolution data corresponding to continuous tone data and high spatial resolution data corresponding to non-continuous tone data.

9. The process of claim 1, wherein following compression, a quantity of compressed non-continuous tone data is decreased to approximately a quarter of a quantity of uncompressed non-continuous tone data present in the plurality of bitwords representing the plurality of pixels.

10. The process 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 a direction of an edge within the image data.

11. The process of claim 1, wherein during decompression, continuous tone data with a low spatial resolution is processed to provide a low spatial resolution bitword-map.

12. The process of claim 11, wherein during decompression, bitwords of information corresponding to discarded non-continuous tone data are synthesized.

13. The process of claim 1, wherein discarding the quantity of bitwords includes discarding three-quarters of the bitwords corresponding to continuous tone data in a high spatial resolution bitword-map to produce low spatial resolution continuous tone data.

14. The process of claim 1, wherein discarding the quantity of bitwords includes discarding half of the bitwords corresponding to non-continuous tone data in one direction of the image data contained in the high spatial resolution bitword-map.

15. The process of claim 14, wherein discarding the quantity of bitwords comprises discarding half of the bitwords corresponding to non-continuous tone data so that resolution is stored in a direction perpendicular to an edge and resolution is discarded in a direction parallel to the edge.

16. The process of claim 14, wherein discarding the quantity of bitwords produces low spatial resolution data corresponding to continuous tone data and high spatial resolution data corresponding to non-continuous tone data.

17. The process of claim 1, wherein each of the bitwords are bytes.

18. The process of claim 17, wherein compressing data indicative of the plurality of explicit pixels remaining after the discarding step into a single bitword comprises:

converting a value indicative of a first pixel from a seven bit value to a three-bit value;

converting a value indicative of a second pixel from a seven bit value to a three-bit value;

establishing a direction bit indicating a direction of an edge located in spaced relationship to the first and second pixels; and

establishing a segmentation bit indicating that the bitword contains non-continuous tone data.

19. The process of claim 18, wherein decompressing the data from the compressed bitword comprises:

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

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

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

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

20. The process of claim 18, wherein the direction bit indicates a direction of synthesis to be performed using the data contained in the decompressed-data-bitword.

21. The process of claim 20, wherein the step of synthesizing is performed in either a fastscan direction or a slowscan direction based on the direction bit.

22. The process of claim 21, wherein the direction bit defines sufficient information for determining which pixel positions are to be synthesized during decompression.

23. The process of claim 22, further comprising rendering twice as many pixels in a direction perpendicular to an edge indicated by the direction bit.

24. The process of claim 22, wherein, when the direction bit indicates a vertical edge, high frequency spatial resolution is performed in the vertical direction by 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.

25. The process of claim 22, wherein, when the direction bit indicates a horizontal edge, high frequency spatial resolution is performed in the horizontal direction by 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.

26. An image data compression and decompression process comprising:

discarding every other pixel in an image, each pixel being indicated by a single byte of data within a bytemap;

reducing the number of bits necessary to render non-continuous tone data pixels;

compressing the data necessary to render two pixels of non-continuous tone data into a single byte of compressed data; and

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

27. The process of claim 26, further comprising, following compression, transmitting the byte of compressed data to a print engine where the step of decompressing is performed, the step of decompressing including extracting the data necessary to render the two non-continuous tone data pixels and fabricating two more non-continuous tone data pixels in a low-spatial resolution direction based on the values of the extracted data.

28. A compression and decompression system for compressing and decompressing image data, the system comprising:

a compressor that compresses image data represented in a bitword-map based on a type of data contained in regions of the bitword-map to produce a compressed-data-bitword-map, wherein the compressor processes the bitword-map to provide both low spatial resolution continuous tone data and to provide high spatial resolution non-continuous tone data, the high spatial resolution non-continuous tone data being provided by storage of extra resolution across edges of marks within an image corresponding to the image data; and

a decompressor that decompresses the compressed-data-bitword-map to provide high spatial resolution data containing non-continuous tone data using the extra resolution across the edges of the marks, and the decompressor decompresses the compressed data bitword-map to provide low spatial resolution continuous tone data.

29. An image forming device, including the compression and decompression system of claim 28.

30. The image forming device of claim 29, wherein the image forming device is a facsimile machine, a laser printer, an inkjet printer, a digital copier or a full-width-print bar printer.

31. A method for compressing image data representing a plurality of pixels and represented by a plurality of bitwords, each pixel corresponding to a separate bitword, the method comprising:

discarding a quantity of bitwords along a direction of an edge while keeping bitwords across the direction of the edge; and

compressing data indicative of a plurality of explicit pixels remaining after the discarding step into a single compressed-data-bitword.

32. The method of claim 31, wherein compressing the data includes reducing a quantity of bits necessary to represent non-continuous tone data.

33. The method of claim 31, wherein discarding the quantity of bitwords comprises discarding half of the bitwords in the plurality of bitwords.

34. The method of claim 31, wherein discarding the quantity of bitwords comprises discarding half of the bitwords corresponding to non-continuous tone data in the plurality of bitwords.

35. The method of claim 31, wherein discarding the quantity of bitwords comprises discarding three-quarters of the bytes corresponding to continuous tone data in the plurality of bitwords.

36. The method of claim 31, wherein the compressing the data indicative of the plurality of explicit pixels remaining after the discarding step into the single compressed-data-bitword comprises compressing data corresponding only to pixels that contain non-continuous tone data.

37. The method of claim 31, wherein compressing the data includes not compressing any bitwords indicative of continuous tone data so that each pixel of continuous tone data corresponds to a separate bitword of the plurality of bitwords.

38. The method of claim 31, wherein discarding the quantity of bitwords produces low spatial resolution data corresponding to continuous tone data and high spatial resolution data corresponding to non-continuous tone data.

39. The method of claim 31, wherein decreasing a quantity of compressed non-continuous tone data to approximately a quarter of a quantity of uncompressed non-continuous tone data present in the plurality of bitwords representing the plurality of pixels.

40. The method of claim 31, wherein discarding the quantity of bitwords comprises discarding three-quarters of the bitwords corresponding to continuous tone data in a high spatial resolution bitword-map to produce low spatial resolution continuous tone data.

41. The method of claim 31, wherein discarding the quantity of bitwords includes discarding half of the bitwords corresponding to non-continuous tone data in one direction of the image data contained in the high spatial resolution bitword-map.

42. The method of claim 31, wherein discarding the quantity of bitwords comprises discarding half of the bitwords corresponding to non-continuous tone data so that resolution is maintained in a direction perpendicular to an edge and resolution is reduced in a direction parallel to the edge.

43. The method of claim 31, wherein discarding the quantity of bitwords produces low spatial resolution data corresponding to continuous tone data and high spatial resolution data corresponding to non-continuous tone data.

44. The method of claim 31, wherein each of the bitwords are bytes.

45. The method of claim 44, wherein compressing data indicative of the plurality of explicit pixels after the discarding step into a single bitword comprises:

converting a value indicative of a first pixel from a seven bit value to a three-bit value;

converting a value indicative of a second pixel from a seven bit value to a three-bit value;

establishing a direction bit indicating a direction of an edge located in spaced relationship to a first and second pixels; and

establishing a segmentation bit indicating that the bitword contains non-continuous tone data.

46. The method of claim 45, therein the direction bit indicates a direction of synthesis to be performed using the data contained in the decompressed-data-bitword.

47. An image data compression method comprising:

discarding every other pixel in an image, each pixel being indicated by a single byte of data within a bytemap;

reducing the number of bits necessary to render non-continuous tone data pixels; and

compressing the data necessary to render two pixels of non-continuous tone data into a single byte of compressed data.

48. A compression system for compressing image data, the system comprising:

a compressor that compresses image data represented in a bitword-map based on a type of data contained in regions of the bitword-map to produce a compressed-data-bitword-map, wherein the compressor processes the bitword-map to provide both low spatial resolution continuous tone data and to provide high spatial resolution non-continuous tone data, the high spatial resolution non-continuous tone data being provided by storage of extra resolution across edges of marks within an image corresponding to the image data.