Dithering process for producing shaded images on display screens

• US 5,748,163 A
• Filed: 05/17/1993
• Issued: 05/05/1998
• Est. Priority Date: 12/24/1991
• Status: Expired due to Term

• Current Assignee: NVIDIA Corporation
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Han, Robin S.
• Primary Examiner(s): SARAS, STEVEN J
• Application Number:
  US08/061,804
• Time in Patent Office: 1,814 Days
• Field of Search: 358/455, 358/429, 382/54, 382/169, 345/89, 345/88, 345/113, 345/136, 345/139, 345/147, 345/148, 345/149, 345/150, 345/152, 345/153
• US Class Current: 345/88
• CPC Class Codes: G09G 3/2025 the sub-frames having all the same time duration
• CPC Class Codes: G09G 3/2051 with use of a spatial dither pattern
• CPC Class Codes: G09G 3/2077 by a combination of two or more gradation control methods
• CPC Class Codes: G09G 3/3607 for displaying colours or for displaying grey scales with a specific pixel layout, e.g. using sub-pixels display of colours in flat matrix panels other than liquid crystal displays G09G3/2003; grey scales specific for television H04N3/127
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers

Abstract

Shaded or color images are simulated using frame modulation techniques on flat panel displays having an array of binary display elements, i.e., display elements that have only two display states, an ON state and an OFF state. The timing of ON/OFF and OFF/ON state transitions of picture elements within predetermined neighborhoods through the array of display elements is coordinated such that the state transitions occur substantially uniformly in space and time during a multi-frame display sequence. Using a multi-frame sequence 16 frames in duration, 16 shades of gray may be realized on a monochrome display. The number of shades may be increased to 64 using dynamic dithering. Dithering is applied by causing the multi-frame sequence to be 64 frames in duration and dividing the multi-frame sequence into four sub-sequences each 16 frames in duration with the duty cycle of each display element during each of the four 16-frame sub-sequences being allowed to assume one of two adjacent values only such that display noise is minimized. The method may be applied to color displays in which pixel locations have illumination elements each of a different color, for example a red illumination element, a green illumination element and a blue illumination element.

Claims

1. A method of simulating non-monochrome display of images on a display device that has an array of picture elements each having only two display states, an ON state and an OFF state, comprising the steps of:

modulating an ON/OFF duty cycle of each picture element of the array of picture elements during a multi-frame display sequence according to attribute information of respective picture element data to be displayed; and

coordinating the timing of ON/OFF and OFF/ON state transitions of picture elements within each of a plurality of predetermined display neighborhoods throughout the array of picture elements such that the state transitions occur substantially uniformly in space and time, within each display neighborhood, during the multi-frame display sequence

wherein said multiframe sequence is sixty-four frames in duration and is logically divided into four sub-sequences each sixteen frames in duration, sixty-five display shades being realized by causing the ON/OFF duty cycle of each picture element to have a value within the set {0, 1/64, 2/64 . . . 64/64}, and

wherein the ON/OFF duty cycle of each picture element during each of said four sixteen-frame sub-sequences of said sixty-four-frame sequence is caused to have a value within the set {0, 1/16, 2/16 . . . 16/16}.

2. The method of claim 1, comprising the further step of allowing the duty cycle of each picture element during each of said four sixteen-frame sub-sequences of said sixty-four-frame sequence to assume one of two adjacent values only within the set {0, 1/16, 2/16 . . . 16/16}.

3. The method of claim 1, comprising further step of allowing the duty cycle of each picture element during at least one, but not all, of said four sixteen-frame sub-sequences of said sixty-four-frame sequence is allowed to assume only a first of two adjacent values within the set {0, 1/16, 2/16 . . . 16/16} and allowing the duty cycle of each picture element during the others of said four sixteen-frame sub-sequences to assume only a second of said two adjacent values.

4. A method of simulating non-monochrome display of images on a display device that has an array of picture elements each having only two display states, an ON state and an OFF state, comprising the steps of:

modulating an ON/OFF duty cycle of each picture element of the array of picture elements during a multi-frame display sequence according to attribute information of respective picture element data to be displayed; and

coordinating the timing of ON/OFF and OFF/ON state transitions of picture elements within each of a plurality of predetermined display neighborhoods throughout the array of picture elements such that the state transitions occur substantially uniformly in space and time, within each display neighborhood, during the multi-frame display sequence

wherein said multiframe sequence is M×

N frames in duration, M and N being integers, wherein said multiframe sequence is logically divided into M sub-sequences each N frames in duration, wherein M×

N+1 display shades are realized by causing the ON/OFF duty cycle of each picture element to have a value within the set {0, 1/M×

N, 2/M×

N . . . M×

N/M×

N}, and

wherein the ON/OFF duty cycle of each picture element during each of said M N-frame sub-sequences of said M×

N sequence is caused to have a value within the set {0, 1/M, 2/M . . . M/M}.

5. The method of claim 4, comprising the further steps of allowing the duty cycle of each picture element during each of said M N-frame sub-sequences of said M×

N sequence to assume one of two adjacent values only, within the set {0, 1/M, 2/M . . . M/M}.

6. The method of claim 4, comprising the further steps of allowing the duty cycle of each picture element during at least one, but not all, of said M N-frame sub-sequences of said M×

N sequence to assume only a first of two adjacent values, within the set {0, 1/M, 2/M . . . M/M} and allowing the duty cycle each picture element during the other of said M N-frame sub-sequences to assume only a second of said two adjacent values.

7. A method of simulating color display of images on a display device that has an array of picture elements, each picture element having a plurality of illumination elements each of a different color and each having only two display states, an ON state and an OFF state, comprising the steps of:

modulating an ON/OFF duty cycle of at least one illumination element of each picture element of the array of picture elements during a multi-frame display sequence according to attribute information of respective picture element data to be displayed; and

coordinating the timing of ON/OFF and OFF/ON state transitions of illumination elements of a given color within each of a plurality of predetermined display neighborhoods throughout the array of picture elements such that the state transitions occur uniformly in space and time, within each display neighborhood, during the multiframe display sequence

wherein said multi-frame sequence is M×

N frames in duration, M and N being integers, wherein said multi-frame sequence is logically divided into M sub-sequences each N frames in duration,

wherein (M×

N+1)³ display colors are realized by causing the ON/OFF duty cycle of each illumination element to have a value within the set {0, 1/M×

N, 2/M×

N, . . . , M×

N/M×

N}, and

wherein the ON/OFF duty cycle of each illumination element during each of said M N-frame sub-sequences of said M×

N sequence is caused to have a value within the set {0, 1/M, 2/M, . . . , M/M}.

8. The method of claim 7, comprising the further steps of allowing the duty cycle of each illumination element during each of said M N-frame sub-sequences of said M×

N frame sequence to assume one of two adjacent values only, within the set {0, 1/M, 2/M, . . . , M/M}.

9. The method of claim 7, comprising the further steps of allowing the duty cycle of each illumination element during at least one, but not all, of said M N-frame sub-sequences of said M×

N frame sequence to assume only a first of two adjacent values only, within the set {0, 1/M, 2/M, . . . , M/M} and allowing the duty cycle of each illumination element during the other of said M N-frame sub-sequences to assume only a second of said two adjacent values.

10. A display device which simulates non-monochrome display of images, said display device having an array of picture elements, each picture element having only two display states, an ON state and an OFF state, comprising:

modulating means for modulating an ON/OFF duty cycle of each picture element of the array of picture elements during a multi-frame display sequence according to attribute information of respective picture element data to be displayed; and

coordinating means for coordinating the timing of ON/OFF and OFF/ON state transitions of picture elements within each of a plurality of predetermined display neighborhoods throughout the array of picture elements such that the state transitions occur substantially uniformly in space and time, within each display neighborhood, during the multi-frame display sequence

wherein said multiframe sequence is sixty-four frames in duration logically divided into four sub-sequences each sixteen frames in duration,

wherein sixty-five display shades are realized by causing the ON/OFF duty cycle of each picture element to have a value within the set {0, 1/64, 2/64 . . . 64/64}, and

wherein the ON/OFF duty cycle of each picture element during each of said four sixteen-frame sub-sequences of said sixty-four-frame sequence is caused to have a value within the set {0, 1/16, 2/16 . . . 16/16}.

11. The display device of claim 10, further comprising:

means for allowing the duty cycle of each picture element during each of said four sixteen-frame sub-sequences of said sixty-four-frame sequence to assume one of two adjacent values only within the set {0, 1/16, 2/16 . . . 16/16}.

12. The display device of claim 10, further comprising:

means for allowing the duty cycle of each picture element during at least one, but not all, of said four sixteen-frame sub-sequences of said sixty-four-frame sequence to assume only a first of two adjacent values within the set {0, 1/16, 2/16 . . . 16/16} and allowing the duty cycle of each picture element during the others of said four sixteen-frame sub-sequences to assume only a second of said two adjacent values.

13. A display device which simulates non-monochrome display of images, said display device having an array of picture elements, each picture element having only two display states, an ON state and an OFF state, comprising:

modulating means for modulating an ON/OFF duty cycle of each picture element of the array of picture elements during a multi-frame display sequence according to attribute information of respective picture element data to be displayed; and

coordinating means for coordinating the timing of ON/OFF and OFF/ON state transitions of picture elements within each of a plurality of predetermined display neighborhoods throughout the array of picture elements such that the state transitions occur substantially uniformly in space and time, within each display neighborhood, during the multi-frame display sequence,

wherein said multiframe sequence is M×

N frames in duration, M and N being integers, wherein said multiframe sequence is logically divided into M sub-sequences each N frames in duration,

wherein M×

N+1 display shades are realized by causing the ON/OFF duty cycle of each picture element to have a value within the set {0, 1/M×

N, 2/M×

N . . . M×

N/M×

N}, and

wherein the ON/OFF duty cycle of each picture element during each of said M N-frame sub-sequences of said M×

N sequence is caused to have a value within the set {0, 1/M, 2/M . . . M/M}.

14. The display device of claim 13, further comprising:

means for allowing the duty cycle of each picture element during each of said M N-frame sub-sequences of said M×

N sequence to assume one of two adjacent values only, within the set {0, 1/M, 2/M . . . M/M}.

15. The display device of claim 13, further comprising:

means for allowing the duty cycle of each picture element during at least one, but not all, of said M N-frame sub-sequences of said M×

N frame sequence to assume only a first of two adjacent values within the set {0, 1/M, 2/M . . . M/M} and allowing the duty cycle of each picture element during the others of said M N-frame sub-sequences to assume only a second of said two adjacent values.

16. A display device which simulates color display of images, said display device having an array of picture elements, each picture element having a plurality of illumination elements each of a different color and each having only two display states, an ON state and an OFF state, comprising:

modulating means for modulating an ON/OFF duty cycle of at least one illumination element of each picture element of the array of picture elements during a multi-frame display sequence according to attribute information of respective picture element data to be displayed; and

coordinating means for coordinating the timing of ON/OFF and OFF/ON state transitions of illumination elements of a given color within each of a plurality of predetermined display neighborhoods throughout the array of picture elements such that the state transitions occur uniformly in space and time, within each display neighborhood, during the multiframe display sequence,

wherein said multi-frame sequence is M×

N frames in duration, M and N being integers, wherein said multi-frame sequence is logically divided into M sub-sequences each N frames in duration,

wherein (M×

N+1)³ display colors are realized by causing the ON/OFF duty cycle of each illumination element to have a value within the set {0, 1/M×

N, 2/M×

N, . . . , M×

N/M×

N}, and

wherein the ON/OFF duty cycle of each illumination element during each of said M N-frame sub-sequences of said M×

N sequence is caused to have a value within the set {0, 1/M, 2/M, . . . , M/M}.

17. The display device of claim 16, further comprising:

means for allowing the duty cycle of each illumination element during each of said M N-frame sub-sequences of said M×

N frame sequence to assume one of two adjacent values only, within the set {0, 1/M, 2/M, . . . , M/M}.

18. The display device of claim 16, further comprising:

means for allowing the duty cycle of each illumination element during at least one, but not all, of said M N-frame sub-sequences of said M×

N frame sequences to assume only a first of two adjacent values within the set {0, 1/M, 2/M, . . . , M/M} and allowing the duty cycle of each illumination element during the other of said M N-frame sub-sequences to assume only a second of said two adjacent values.