System and method for blinking digitally-commanded pixels of a display screen to produce a palette of many colors

• US 5,122,783 A
• Filed: 07/27/1990
• Issued: 06/16/1992
• Est. Priority Date: 04/10/1989
• Status: Expired due to Term

• Current Assignee: ATI Technologies Incorporated (Advanced Micro Devices, Inc.)
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Bassetti, Chester F. Jr.
• Primary Examiner(s): Brier, Jeffery A.
• Application Number:
  US07/558,903
• Time in Patent Office: 690 Days
• Field of Search: 340/793, 340/767, 340/701, 340/703
• US Class Current: 345/88
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 2320/0261 in the context of movement of objects on the screen or movement of the observer relative to the screen
• CPC Class Codes: G09G 2320/0266 Reduction of sub-frame artefacts
• CPC Class Codes: G09G 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 2360/18 Use of a frame buffer in a display terminal, inclusive of the display panel
• CPC Class Codes: G09G 3/20 for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
• CPC Class Codes: G09G 3/2003 Display of colours specific for liquid crystal displays G09G3/3607
• CPC Class Codes: G09G 3/2007 Display of intermediate tones
• 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 3/2092 Details of a display terminals using a flat panel, the details relating to the control arrangement of the display terminal and to the interfaces thereto suitable for both CRT and flat panel G09G5/003; specific for a CRT G09G1/165
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers
• CPC Class Codes: H04N 3/127 using liquid crystals

Abstract

A frame rate duty cycle technique and dithering technique is applied to the output of a color look-up RAM in order to drive various flat panel displays. An integrated circuit chip in accordance with the invention includes a modulo-N gray scaling unit, where the value N is variable as well as a pixels dithering unit and a color mixing unit. A brightness spreading memory is included for mapping CRT drive values into LCD drive values.

Claims

1. A method of generating a pixel having a mixed color on a digitally commanded display, wherein the mixed color is formed from specified primary colors, each having a specified brightness, and the pixel comprises a plurality of colored sub-pixels and wherein each sub-pixel corresponds to a different one of the specified primary colors, the method comprising:

blinking each colored sub-pixel of the pixel at a selected rate to thereby set a unique time-averaged brightness for that sub-pixel over a selected plurality of frames, wherein the time-averaged brightness corresponds to the brightness specified for the selected primary color being provided by that sub-pixel.

2. The method of claim 1, wherein each sub-pixel has a ON state and an OFF state, and wherein in the blinking step the sub-pixel is commanded to be ON during a specified number of the selected plurality of frames, and commanded to be OFF during the remainder of the selected plurality of frames.

3. The method of claim 2, wherein the mixed color to be generated is specified by a digital code intended for use with a cathode ray tube display which produces primary colors of specific hues, and the digitally commanded display produces primary colors of hues different from those of the cathode ray tube display, further including the step of

correcting for the difference in hues by mixing in amounts of the other primary colors.

4. The method of claim 2, wherein the sub-pixel is commanded to be OFF or ON by way of a brightness setting waveform having a plurality of consecutive bits in which each bit corresponds to a different phase of the brightness setting waveform and each phase of the brightness setting waveform provides a command for a frame in the selected plurality of frames, further including the steps of

generating the mixed color for a plurality of adjacent pixels arrange din rows and columns;

and

applying different phases of the brightness setting waveform to sub-pixels of pixels adjacent one another, so that no two adjacent pixels receive the same phase of the brightness setting waveform at the same time.

5. The method of claim 4 wherein the applying step includes the step of

defining a wrap-around sequence of a predetermined number of pixels in length, which designates a different phase from pixel to pixel with which the corresponding brightness waveform is to be applied to the sub-pixels of each pixel of the display;

defining a phase placement pattern which is associated with the brightness setting waveform, and which is constructed of the corresponding wrap around sequence, wherein the phase placement pattern for the corresponding wrap-around sequence is used in each row.

6. The method of claim 5, wherein the phase placement pattern for the corresponding wrap-around sequence is used in each row, but offset every A-rows by B-pixels.

7. An apparatus for generating a pixel having a mixed color on a digitally commanded display, wherein the mixed color is formed from specified primary colors, each having a specified brightness, and the pixel comprises a plurality of colored sub-pixels each sub-pixel corresponding to a different one of the specified primary colors, the apparatus comprising:

means for blinking each colored sub-pixel of the pixel at a selected rate over a selected plurality of frames to thereby set a unique time-averaged brightness for that sub-pixel corresponding to the brightness specified for the primary color being provided by that sub-pixel.

8. The apparatus of claim 7, wherein the blinking means comprise a plurality of gray scale generating means, each associated with a different one of the specified primary colors, for generating a brightness setting waveform which controls the state of an associated primary sub-pixel over the selected plurality of consecutive frames, wherein the brightness setting waveform commands the sub-pixel for the associated color towards an ON state during a specified number of the selected plurality of frames, and commands the sub-pixel towards an OFF state during the remainder of the selected plurality of consecutive frames.

9. The apparatus of claim 8, wherein the mixed color is generated for a plurality of adjacent pixels arranged in rows and columns, and further wherein the brightness setting waveform has a plurality of consecutive bits in which each bit corresponds to a different phase of the brightness setting waveform and each phase of the brightness setting waveform provides a command for a frame in the selected plurality of consecutive frames, and further including

means for applying different phases of the brightness setting waveform to sub-pixels of pixels adjacent one another, so that no two adjacent pixels receive the same phase of the brightness setting waveform at the same time.

10. The apparatus of claim 9 wherein the applying means includes

means for defining a wrap-around sequence of a predetermined number of pixels in length, which designates a different phase from pixel to pixel with which the corresponding brightness waveform is to be applied to the sub-pixels of each pixel of the display;

and

means for defining a phase placement pattern which is associated with the brightness setting waveform, and which is constructed of the corresponding wrap around sequence, wherein the phase placement pattern for the corresponding wrap-around sequence is used in each row of the plurality of pixels.

11. An apparatus for controlling a pixel on a digitally commanded display to produce a mixed color, wherein the mixed color is formed from specified primary colors, each having a specified brightness, and further wherein the pixel comprises a plurality of colored sub-pixels, each of which provides a different one of the specified primary colors, the apparatus comprising:

a plurality of means each of which is associated with a different one of the sub-pixels for controlling the associated sub-pixel using a frame rate duty cycle approach to produce over a designated plurality of consecutive frames a time-averaged brightness which corresponds to the brightness specified for the primary color provided by the sub-pixel, wherein the sub-pixel is commanded to be either ON or OFF during each frame in the designated plurality of consecutive frames.

12. The apparatus of claim 11, wherein sub-pixel provides a primary color having a hue which is different from a desired primary color, and further including

color matching means for adjusting the primary color produced by the sub-pixel by controlling others of the sub-pixels to provide selected adjustment intensities of their associated primary colors, so that the combined intensities of the primary colors provide an adjusted primary color which substantially matches the hue of the desired primary color.

13. The apparatus of claim 12 wherein CRT intensities are specified for red, blue and green primary colors which provide a first color when mixed, wherein in the digitally commanded display a red sub-pixel provides a red primary color, a blue sub-pixel provides a blue primary color, and a green sub-pixel provides a green primary color, and further wherein the red, green and blue sub-pixels provide primary colors having hues which are different from desired primary color hues, and further wherein adjustment intensities of the red, blue and green sub-pixels are specified for adjusting the respective primary colors provided by each of the sub-pixels, and further wherein the color matching means comprise

red multiplying means for forming multiplication products between the specified red CRT intensity and the red sub-pixel adjustment intensity specified for adjusting the red sub-pixel primary color, between the specified green CRT intensity and the green sub-pixel adjustment intensity specified for adjusting the red sub-pixel primary color, and between the specified blue CRT intensity and the blue sub-pixel adjustment intensity specified for adjusting the red sub-pixel primary color;

red summing means coupled to the red multiplying means for summing together the formed multiplication products to provide an adjusted red sub-pixel intensity;

green multiplying means for forming multiplication products between the specified red CRT intensity and the red sub-pixel adjustment intensity specified for adjusting the green sub-pixel primary color, between the specified green CRT intensity and the green sub-pixel adjustment intensity specified for adjusting the green sub-pixel primary color, and between the specified blue CRT intensity and the blue sub-pixel adjustment intensity specified for adjusting the green sub-pixel primary color;

green summing means coupled to the green multiplying means for summing together the formed multiplication products to provide an adjusted green sub-pixel intensity;

blue multiplying means for forming multiplication products between the specified red CRT intensity and the red sub-pixel adjustment intensity specified for adjusting the blue sub-pixel primary color, between the specified green CRT intensity and the green sub-pixel adjustment intensity specified for adjusting the blue sub-pixel primary color, and between the specified blue CRT intensity and the blue sub-pixel adjustment intensity specified

for adjusting the blue sub-pixel primary color; and

blue summing means coupled to the blue multiplying means for summing together the formed multiplication products to provide an adjusted blue sub-pixel intensity.

14. The apparatus of claim 13 wherein the red, blue and green multiplying means are each a multiply and shift module.

15. The apparatus of claim 11 wherein a number, N, of CRT mixed colors is specified and a number, M, of brightnesses can be generated by each of the plurality of controlling means, further including

means for mapping each of the N CRT mixed colors to the M brightness levels.

16. The apparatus of claim 11 further including in each of the plurality of controlling means:

means for defining a square matrix of pixels on the digitally commanded display; and

means for controlling a sub-pixel of at least one of the of pixels in the square matrix to have a first brightness, and for controlling a sub-pixel in each of the remainder of the pixels in the square matrix to have a second brightness different from the first brightness, so that an effective brightness is provided for the square matrix which falls in between the first and second brightnesses.

17. The apparatus of claim 11 wherein each of the plurality of controlling means includes

fixed means for controlling the associated sub-pixel using a frame rate duty cycle approach to produce a fixed number of time averaged brightnesses over a fixed number of consecutive frames, wherein the sub-pixel is commanded to be either ON or OFF during each frame in the predetermined number of consecutive frames;

and

programmable means for controlling the associated sub-pixel using a frame rate duty cycle approach to produce a programmable number of time averaged brightnesses over a programmable number of consecutive frames, wherein the sub-pixel is commanded to be either ON or OFF during each frame in the predetermined number of consecutive frames.

18. The apparatus of claim 11 wherein each of the plurality of controlling means provide a programmable number of time averaged brightnesses over a programmable number of consecutive frames.