Raster-order pixel dithering

• US 7,978,200 B1
• Filed: 12/28/2006
• Issued: 07/12/2011
• Est. Priority Date: 12/28/2006
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Childs, John S., Lillie, Jeffrey, Small, Jeffrey A., Misic, Vladimir
• Primary Examiner(s): Tung; Kee M
• Assistant Examiner(s): AMIN, JWALANT B
• Application Number:
  US11/648,839
• Time in Patent Office: 1,657 Days
• Field of Search: None
• US Class Current: 345/559
• CPC Class Codes: G09G 3/2044 using dithering
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers

Abstract

Stochastic dithering may be used to reduce the size of the frame buffer and the complexity of the D/A Converters (DACs) in the drive circuitry that are used in a video display system. Hardware for stochastic dithering can be simplified when pixel data is presented in raster order. The hardware adds algebraic noise to the image to be dithered, and thresholds the result.

Claims

1. An apparatus for generating stochastic dither values in raster order for pixels of a frame, comprising:

a raster address generator that is configured to generate line and column addresses in a raster order;

a first register and a second register, wherein;

the first register is configured to store a current value X0 of the second register in response to a new line signal and to store a value of (M+A) mod C in response to a new column signal, where M is a current value of the first register, A is a constant, and C is a number of pixels in a line; and

the second register is configured to store a value of (X0+B) mod C in response to the new line signal, where B is a constant, and where A, B and C are mutually prime; and

an output configured to provide the value in the first register as a dither value.

2. The apparatus of claim 1, further comprising:

an adder that is configured to add an input pixel that corresponds to a current raster line and column address to the dither value provided by the output.

3. The apparatus of claim 1, wherein the apparatus is configured to calculate and store the values in the first and second registers in real time within a time required to display a line of video information divided by the number of pixels in the line.

4. The apparatus of claim 1, wherein:

the pixels comprise red, blue, and green color components; and

each color component has at least two bits.

5. The apparatus of claim 1, further comprising an adder that is configured to add a value determined from local image information to the dither value provided by the output.

6. The apparatus of claim 1, further comprising an adder that is configured to add a value determined from global image information to the dither value provided by the output.

7. The apparatus of claim 1, wherein the output is configured to:

provide the value in the first register as a first dither value;

provide a value of a first function of the first dither value as a second dither value; and

provide a value of a second function of the first dither value as a third dither value.

8. The apparatus of claim 7, wherein:

the first function is (M+C/3) mod C; and

the second function is (M+2C/3) mod C.

9. A method for generating stochastic dither values in raster order for pixels of a frame, comprising:

generating line and column addresses in a raster order;

storing, in a first register, a current value X0 of a second register in response to a new line signal and a value of (M+A) mod C in response to a new column signal, where M is a current value of the first register, A is a constant, and C is a number of pixels in a line;

storing, in the second register, a value of (X0+B) mod C in response to the new line signal, where B is a constant, and where A, B and C are mutually prime; and

outputting the value in the first register as a dither value.

10. The method of claim 9, further comprising adding input pixel information that corresponds to a current raster line and column address to the output dither value.

11. The method of claim 9, wherein the values are calculated and stored in the first and second registers within a time required to display a line of video information divided by the number of pixels in the line.

12. The method of claim 9, wherein:

the pixels comprise red, blue, and green color components; and

each color component has at least two bits.

13. The method of claim 9, further comprising adding a value determined from local image information to the output dither value.

14. The method of claim 9, further comprising adding a value determined from global image information to the output dither value.

15. The method of claim 9, further comprising:

providing the value in the first register as a first dither value;

providing a value of a first function of the first dither value as a second dither value; and

providing a value of a second function of the first dither value as a third dither value.

16. The apparatus of claim 15, wherein:

the first function is (M+C/3) mod C; and

the second function is (M+2C/3) mod C.

17. An apparatus for dithering reduced-bit depth pixels, comprising:

means for generating line and column addresses in a raster order;

first and second means for storing, wherein;

the first means for storing is configured to store a current value X0 of the second means for storing in response to a new line signal and to store a value of (M+A) mod C in response to a new column signal, where M is a current value of the first means for storing, A is a constant, and C is a number of pixels in a line; and

the second means for storing is configured to store a value of (X0+B) mod C in response to the new line signal, where B is a constant, and where A, B and C are mutually prime; and

means for outputting the value in the first register as a dither value.

18. The apparatus of claim 17, further comprising means for adding input pixel information that corresponds to a current raster row and column address to the output dither value.

19. An apparatus for dithering raster-order image data, comprising:

a dither matrix generation circuit; and

an adder circuit configured to add first, second, and third dither matrix values from the dither matrix generation circuit to first, second, and third color components, respectively, of the image data;

wherein the dither matrix generation circuit comprises a first register and a second register;

wherein the first register is configured to store a current value X0 of the second register in response to a new line signal and to store a value of (M+A) mod C in response to a new column signal, where M is a current value of the first register, A is a constant, and C is a constant;

wherein the second register is configured to store a value of (X0+B) mod C in response to the new line signal, where B is a constant, and where A, B, and C are mutually prime; and

wherein the first dither matrix value is the value in the first register, the second dither matrix value is a value of a first function of the first dither matrix value, and the third dither matrix value is a value of a second function of the first dither matrix value.

20. The apparatus of claim 19, wherein:

the first function is (M+C/3) mod C; and

the second function is (M+2C/3) mod C.