Claims
- 1. An apparatus for enhancing the gray shade rendering capability of a display device, said display device having a frame rate of q frames per display cycle, comprising:
- a first comparator for comparing an intensity value representing a gray shade of a current pixel with a respective dither matrix threshold value and for providing a pixel on/off signal;
- a quantization table for storing a plurality of quantization values ranging from 1 to q and for outputting p quantization values as active quantization values in accordance with a quantized pixel value p and for shifting said quantization values in said table in response to a frame signal;
- a second comparator for comparing a quantized dither matrix threshold value to said active quantization values to produce an active quantized threshold signal;
- a pixel out generator responsive to said pixel on/off signal and said active quantized threshold signal for producing a pixel out signal;
- a display responsive to said pixel out signal for displaying said current pixel with an average gray value of p/q through a display period of q frames.
- 2. An apparatus as in claim 1 further comprising a dither matrix for storing a plurality of threshold values.
- 3. An apparatus as in claim 2 further comprising at least one counter responsive to coordinates of a current pixel for addressing said dither matrix to output said respective dither matrix threshold value.
- 4. An apparatus as in claim 2 further comprising a multi-thresholding unit for quantizing said respective dither matrix threshold value to produce a quantized dither matrix threshold value ranging from 1 to q.
- 5. An apparatus as in claim 2 further comprising a dither matrix generator for generating said dither matrix, comprising:
- means for generating a dither matrix of dither-matrix locations that contain dither-matrix thresholds and are associated with respective subregion pixels of an image subregion by repeatedly assigning thresholds to the dither-matrix locations;
- means for determining for each of a plurality of the subregion pixels the relative tightness thereto with which are clustered thereabout pixels that receive dots when the subregion presents a uniform gray-scale level that corresponds to the threshold being assigned;
- means for identifying each subregion pixel for which the tightness thereby determined is greatest;
- means for determining for each of a plurality of the subregion pixels thus identified the relative tightness thereto with which are clustered thereabout subregion pixels that have been assigned thresholds whose ranks is in a rank range that depends on the threshold being assigned and excludes some subregion pixels that receive dots when the subregion presents the uniform gray-scale level that corresponds to the threshold being assigned;
- means for selecting at least one subregion pixel for which the tightness thereby determined is greatest; and
- means for assigning the threshold to a dither-matrix location associated with a subregion pixel thus selected.
- 6. An apparatus as in claim 1 further comprising a multi-thresholding unit for quantizing said intensity value representing a gray shade of said current pixel to produce said quantized pixel value p ranging from 1 to q.
- 7. An apparatus as in claim 1 wherein said quantization table comprises a shift register.
- 8. An apparatus as in claim 7 wherein said quantization table comprises a circular shift register.
- 9. An apparatus as in claim 7 wherein said quantization table comprises a circular, linear shift register.
- 10. An apparatus as in claim 1 wherein said display is a liquid crystal display (LCD).
- 11. A method for enhancing the gray shade rendering capability of a display device, said display device having a frame rate of q frames per display cycle, comprising:
- comparing an intensity value representing a gray shade of a current pixel with a respective dither matrix threshold value and providing a pixel on/off signal;
- storing a plurality of quantization values ranging from 1 to q in a quantization table;
- outputting p quantization values from said quantization table as active quantization values in accordance with a quantized pixel value p;
- shifting said quantization values in said table in response to a frame signal;
- comparing a quantized dither matrix threshold value to said active quantization values and producing an active quantized threshold signal;
- producing a pixel out signal in response to said pixel on/off signal and said active quantized threshold signal;
- in response to said pixel out signal displaying said current pixel with an average gray value of p/q through a display period of q frames.
- 12. A method as in claim 11 further comprising storing a plurality of threshold values in a dither matrix.
- 13. A method as in claim 12 further comprising addressing said dither matrix in response to coordinates of a current pixel and outputting said respective dither matrix threshold value.
- 14. A method as in claim 12 further comprising quantizing said respective dither matrix threshold value to produce a quantized dither matrix threshold value ranging from 1 to q.
- 15. A method as in claim 12 further comprising generating said dither matrix, said dither matrix generating step comprising:
- generating a dither matrix of dither-matrix locations that contain dither-matrix thresholds and are associated with respective subregion pixels of an image subregion by repeatedly assigning thresholds to the dither-matrix locations;
- determining for each of a plurality of the subregion pixels the relative tightness thereto with which are clustered thereabout pixels that receive dots when the subregion presents a uniform gray-scale level that corresponds to the threshold being assigned;
- identifying each subregion pixel for which the tightness thereby determined is greatest;
- determining for each of a plurality of the subregion pixels thus identified the relative tightness thereto with which are clustered thereabout subregion pixels that have been assigned thresholds whose ranks is in a rank range that depends on the threshold being assigned and excludes some subregion pixels that receive dots when the subregion presents the uniform gray-scale level that corresponds to the threshold being assigned;
- selecting at least one subregion pixel for which the tightness thereby determined is greatest; and
- assigning the threshold to a dither-matrix location associated with a subregion pixel thus selected.
- 16. A method as in claim 11 further comprising quantizing said intensity value representing a gray shade of said current pixel to produce said quantized pixel value p ranging from 1 to q.
- 17. A method as in claim 11 further comprising storing said quantization table in a shift register.
- 18. A method as in claim 17 further comprising shifting said quantiztion values in said quantization table circularly.
- 19. A method as in claim 17 further comprising storing said quantization values linearly in said quantization table.
- 20. A method as in claim 11 further comprising displaying said current pixel on a liquid crystal display (LCD).
- 21. A medium readable by a machine embodying a program of instructions executable by said machine to perform a method of enhancing the gray shade rendering capability of a display device, said display device having a frame rate of q frames per display cycle, said enhancing method comprising:
- comparing an intensity value representing a gray shade of a current pixel with a respective dither matrix threshold value and providing a pixel on/off signal;
- storing a plurality of quantization values ranging from 1 to q in a quantization table;
- outputting p quantization values from said quantization table as active quantization values in accordance with a quantized pixel value p;
- shifting said quantization values in said table in response to a frame signal;
- comparing a quantized dither matrix threshold value to said active quantization values and producing an active quantized threshold signal;
- producing a pixel out signal in response to said pixel on/off signal and said active quantized threshold signal;
- in response to said pixel out signal displaying said current pixel with an average gray value of p/q through a display period of q frames.
- 22. A medium as in claim 21 wherein said enhancing method further comprises storing a plurality of threshold values in a dither matrix.
- 23. A medium as in claim 22 wherein said enhancing method further comprises addressing said dither matrix in response to coordinates of a current pixel and outputting said respective dither matrix threshold value.
- 24. A medium as in claim 22 wherein said enhancing method further comprises quantizing said respective dither matrix threshold value to produce a quantized dither matrix threshold value ranging from 1 to q.
- 25. A medium as in claim 22 wherein said enhancing method further comprises generating said dither matrix, said dither matrix generating step comprising:
- generating a dither matrix of dither-matrix locations that contain dither-matrix thresholds and are associated with respective subregion pixels of an image subregion by repeatedly assigning thresholds to the dither-matrix locations;
- determining for each of a plurality of the subregion pixels the relative tightness thereto with which are clustered thereabout pixels that receive dots when the subregion presents a uniform gray-scale level that corresponds to the threshold being assigned;
- identifying each subregion pixel for which the tightness thereby determined is greatest;
- determining for each of a plurality of the subregion pixels thus identified the relative tightness thereto with which are clustered thereabout subregion pixels that have been assigned thresholds whose ranks is in a rank range that depends on the threshold being assigned and excludes some subregion pixels that receive dots when the subregion presents the uniform gray-scale level that corresponds to the threshold being assigned;
- selecting at least one subregion pixel for which the tightness thereby determined is greatest; and
- assigning the threshold to a dither-matrix location associated with a subregion pixel thus selected.
- 26. A medium as in claim 21 wherein said enhancing method further comprises quantizing said intensity value representing a gray shade of said current pixel to produce said quantized pixel value p ranging from 1 to q.
- 27. A medium as in claim 21 wherein said enhancing method further comprises storing said quantization table in a shift register.
- 28. A medium as in claim 27 wherein said enhancing method further comprises shifting said quantiztion values in said quantization table circularly.
- 29. A medium as in claim 27 wherein said enhancing method further comprises storing said quantization values linearly in said quantization table.
- 30. A medium as in claim 21 wherein said enhancing method further comprises displaying said current pixel on a liquid crystal display (LCD).
- 31. A system for displaying a source image having a number of available gray shades represented by N bits per pixel on a display device having an M level gray shade display capability where M is less than 2.sup.N, comprising:
- an input device for providing said source image;
- a display device having a frame rate of q frames per display cycle:
- a first comparator for comparing an intensity value representing a gray shade of a current pixel of said source image with a respective dither matrix threshold value and for providing a pixel on/off signal;
- a quantization table for storing a plurality of quantization values ranging from 1 to q and for outputting p quantization values as active quantization values in accordance with a quantized pixel value p and for shifting said quantization values in said table in response to a frame signal;
- a second comparator for comparing a quantized dither matrix threshold value to said active quantization values to produce an active quantized threshold signal;
- a pixel out generator responsive to said pixel on/off signal and said active quantized threshold signal for producing a pixel out signal;
- a display responsive to said pixel out signal for displaying said current pixel with an average gray value of p/q through a display period of q frames.
- 32. A system as in claim 31 wherein said input device is a scanner.
- 33. A system as in claim 31 wherein said input device is a personal computer.
- 34. A system as in claim 31 wherein said input device is a digital camera.
- 35. A system as in claim 31 wherein said input device is media.
- 36. A system as in claim 31 wherein said display device is a computer.
- 37. A system as in claim 31 wherein said display device is a projector.
- 38. A system as in claim 31 wherein said display is a liquid crystal display (LCD).
RELATED APPLICATIONS
This application is a continuation-in-part of pending, prior application Ser. No. 08/890,611 filed Jul. 9, 1997, which is incorporated herein in its entirety by reference.
US Referenced Citations (13)
Foreign Referenced Citations (3)
Number |
Date |
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WO 8906851 |
Jul 1989 |
WOX |
WO 9003023 |
Mar 1990 |
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Continuation in Parts (1)
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Number |
Date |
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Parent |
890611 |
Jul 1997 |
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