Frame buffer compression and decompression method for graphics rendering

• US 8,031,937 B2
• Filed: 12/10/2007
• Issued: 10/04/2011
• Est. Priority Date: 04/04/2007
• Status: Active Grant

• Current Assignee: Interdigital Vc Holdings, Inc. (InterDigital, Inc.)
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Munkberg, Jacob, Hasselgren, Jon, Rasmusson, Jim, Akenine-Möller, Tomas
• Primary Examiner(s): Alavi; Amir
• Application Number:
  US11/953,339
• Publication Number:
  US 20080247641A1
• Time in Patent Office: 1,394 Days
• Field of Search: 382/162, 382/164, 382/166, 382/168, 382/173, 382/232, 382236-238, 382244-246, 382/274, 382/305, 345418-420, 345/555, 345/582, 345/612, 345/613, 375/240.24, 375/240.27, 375/355, 348/111, 348/169, 348/672, 701/213
• US Class Current: 382/166
• CPC Class Codes: G06T 11/40 Filling a planar surface by adding surface attributes, e.g. colour or texture
• CPC Class Codes: G09G 2340/02 Handling of images in compressed format, e.g. JPEG, MPEG
• CPC Class Codes: G09G 2340/10 Mixing of images, i.e. displayed pixel being the result of an operation, e.g. adding, on the corresponding input pixels
• CPC Class Codes: G09G 5/363 Graphics controllers
• CPC Class Codes: G09G 5/393 Arrangements for updating the contents of the bit-mapped memory
• CPC Class Codes: H04N 19/12 Selection from among a plurality of transforms or standards, e.g. selection between discrete cosine transform [DCT] and sub-band transform or selection between H.263 and H.264
• CPC Class Codes: H04N 19/147 according to rate distortion criteria rate-distortion as a criterion for motion estimation H04N19/567
• CPC Class Codes: H04N 19/154 Measured or subjectively estimated visual quality after decoding, e.g. measurement of distortion use of rate-distortion criteria H04N19/147
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/40 using video transcoding, i.e. partial or full decoding of a coded input stream followed by re-encoding of the decoded output stream
• CPC Class Codes: H04N 19/423 characterised by memory arrangements H04N19/433 takes precedence

Abstract

Methods and apparatus are disclosed for the processing of frame buffer data, such as color buffer data, in graphics processing applications. Although more generally applicable, these methods and apparatus are particularly useful in real-time, polygon-based, 3D rendering applications. An exemplary method for processing graphics data according to one or more embodiments of the invention begins with the retrieval, from a buffer, of pixel values corresponding to a tile of two or more pixels, and with the updating of one or more of those updated pixel values. The updated pixel values are selectively compressed using a lossy compression operation or a lossless compression operation, based on an accumulated error metric value for the tile. If lossy compression is used, then the accumulated error metric value for the tile is updated; in either event, the compressed pixel values are stored in the frame buffer for further processing. With this approach, the accumulated error caused by successive, or tandem, compression operations may be limited to a pre-determined maximum.

Claims

1. A method for processing graphics data, comprising:

retrieving, from a frame buffer, pixel values corresponding to a tile of two or more pixels;

updating, by a graphics processor, one or more of the pixel values to obtain updated pixel values;

selectively compressing the updated pixel values, by the graphics processor using a lossy compression operation or a lossless compression operation, based on an accumulated error metric value for the tile;

updating the accumulated error metric value if lossy compression is used; and

storing the compressed pixel values in the frame buffer.

2. The method of claim 1, wherein selectively compressing the updated pixel values comprises predicting the effect of the lossy compression on the accumulated error metric value, and using the lossy compression operation or the lossless compression operation based on the predicted effect.

3. The method of claim 1, wherein selectively compressing the updated pixel values comprises predicting the effects of two or more lossy compression operations on the accumulated error metric value and selecting the lossless compression operation or one of the two or more lossy compression operations, based on the predicted effect.

4. The method of claim 1, wherein selectively compressing the updated pixel values comprises using the lossless compression operation if the accumulated error metric value exceeds a pre-determined threshold and otherwise using the lossy compression operation.

5. The method of claim 4, wherein otherwise using the lossy compression operation comprises selecting the lossy compression operation from two or more candidate lossy compression operations based on the accumulated error metric value.

6. The method of claim 4, wherein the pixel values comprise pixel color values, and wherein the method further comprises selecting the pre-determined threshold based on whether the updated pixel values comprise alpha values.

7. The method of claim 1, wherein the lossless compression operation comprises entropy encoding of residual errors from neighbor-based predictors of pixel values.

8. The method of claim 7, wherein entropy encoding of residual errors comprises Golomb-Rice coding.

9. The method of claim 1, wherein the lossy compression operation comprises one or more of quantization, subsampling, or averaging of the updated pixel values.

10. The method of claim 1, wherein the pixel values comprise pixel color values and wherein the lossy compression operation comprises compressing luminance components of the updated pixel values using a lossless algorithm and compressing chrominance components of the updated pixel values using a lossy algorithm.

11. The method of claim 10, wherein the lossless algorithm comprises Golomb-Rice encoding of residual errors from neighbor-based predictors of luminance values for the updated pixel values, and wherein the lossy algorithm comprises one or more of quantization, subsampling, or averaging of the chrominance components of the updated pixel values.

12. The method of claim 1, wherein the pixel values comprise pixel color values and wherein the method further comprises transforming the pixel values from a first color space to a second color space before updating one or more of the pixel values and transforming the updated pixel values from the second color space to the first color space before selectively compressing the updated pixel values.

13. The method of claim 12, wherein the second color space comprises the RGB color space and wherein the first color space comprises a reversible, bit-exact transform of the first color space.

14. The method of claim 13, wherein the first color space comprises the YCoCg color space.

15. An apparatus for processing graphics data, comprising

a frame buffer and

a graphics processor configured to:

retrieve, from the frame buffer, pixel values corresponding to a tile of two or more pixels;

update one or more of the pixel values to obtain updated pixel values;

selectively compress the updated pixel values using a lossy compression operation or a lossless compression operation, based on an accumulated error metric value for the tile;

update the accumulated error metric value if lossy compression is used; and

store the compressed pixel values in the frame buffer.

16. The apparatus of claim 15, wherein the graphics processor is configured to selectively compress the updated pixel values by predicting the effect of the lossy compression on the accumulated error metric value and using the lossy compression operation or the lossless compression operation based on the predicted effect.

17. The apparatus of claim 15, wherein the graphics processor is configured to selectively compress the updated pixel values by predicting the effects of two or more lossy compression operations on the accumulated error metric value and selecting the lossless compression operation or one of the two or more lossy compression operations, based on the predicted effects.

18. The apparatus of claim 15, wherein the graphics processor is configured to compress the updated pixel values using the lossless compression operation if the accumulated error metric value exceeds a pre-determined threshold and using the lossy compression operation otherwise.

19. The apparatus of claim 18, wherein the graphics processor is further configured to select the lossy compression operation from two or more candidate lossy compression operations based on the accumulated error metric value if the accumulated error metric value does not exceed the pre-determined threshold.

20. The apparatus of claim 18, wherein the pixel values comprise pixel color values and wherein the graphics processor is further configured to select the pre-determined threshold based on whether the updated pixel values comprise alpha values.

21. The apparatus of claim 15, wherein the pixel values comprise pixel color values and wherein the lossy compression operation comprises compressing luminance components of the updated pixel values using a lossless algorithm and compressing chrominance components of the updated pixel values using a lossy algorithm.

22. The apparatus of claim 15, wherein the pixel values comprise pixel color values and wherein the graphics processor is further configured to transform the pixel values from a first color space to a second color space before updating one or more of the pixel values and to transform the updated pixel values from the second color space to the first color space before selectively compressing the updated pixel values.

23. The apparatus of claim 22, wherein the second color space comprises the RGB color space and wherein the first color space comprises a reversible, bit-exact transform of the first color space.

24. The apparatus of claim 23, further comprising a display and a display driver, wherein the display driver is configured to:

retrieve the stored, compressed, updated pixel values from the frame buffer;

decompress the retrieved, compressed updated pixel values;

transform the updated pixel values from the first color space to the RGB color space; and

provide the transformed, updated pixel values to the display.