Fixed length coding based image data compression

1. A method of compressing an image data block, the method comprising:

computing a pixel residual for each pixel in the image data block except a non-residual pixel;

computing a compression level for the image data block based on a minimum pixel residual value and a maximum pixel residual value of the pixel residuals;

encoding a compression flag for the image data block, wherein the compression flag includes an indicator identifying the compression level and a first portion of bits from the non-residual pixel; and

generating a compressed block comprising a second portion of bits from the non-residual pixel and the pixel residuals encoded using fixed length coding based on the compression level.

2. The method of claim 1 , wherein the compression level specifies a number of bits in a codeword of the fixed length coding.

3. The method of claim 2 , wherein the compression level is one of n compression levels, wherein n is a number of bits in a pixel and each of the n compression levels specifies a different number of bits.

4. The method of claim 3 , wherein the compression level is one of a subset of compression levels selected from the n compression levels.

5. The method of claim 3 , wherein the first portion of bits includes a same number of bits as specified by the compression level and the second portion of bits includes remaining bits in the non-residual pixel.

6. The method of claim 1 , wherein computing a pixel residual further comprises spatially predicting each pixel except the non-residual pixel based on at least one neighboring pixel in the image data block.

7. The method of claim 6 , wherein computing a pixel residual further comprises spatially predicting a pixel based on a top neighboring pixel, a top left neighboring pixel, and a left neighboring pixel.

8. The method of claim 1 , wherein computing a pixel residual further comprises computing a pixel residual for a pixel as a difference between a value of the pixel and a minimum pixel value in the image data block.

9. The method of claim 2 , further comprising:

storing the compressed block in a compressed data buffer in external memory; and

storing the compression flag in a compression flag buffer.

10. The method of claim 9 , further comprising storing the image data block in the compressed data buffer when the compression level specifies a number of bits equal to a number of bits in a pixel.

11. A digital system comprising:

means for computing a pixel residual for each pixel in an image data block except a non-residual pixel;

means for computing a compression level for the image data block based on a minimum pixel residual value and a maximum pixel residual value of the pixel residuals;

means for encoding a compression flag for the image data block, wherein the compression flag includes an indicator identifying the compression level and a first portion of bits from the non-residual pixel;

means for encoding the pixel residuals using fixed length coding based on the compression level; and

means for generating a compressed block comprising a second portion of bits from the non-residual pixel and the pixel residuals encoded using fixed length coding based on the compression level.

12. The digital system of claim 11 , wherein the compression level specifies a number of bits in a codeword of the fixed length coding.

13. The digital system of claim 12 , wherein the compression level is one of n compression levels, wherein n is a number of bits in a pixel and each of the n compression levels specifies a different number of bits.

14. The digital system of claim 13 , wherein the compression level is one of a subset of compression levels selected from the n compression levels.

15. The digital system of claim 12 , wherein the first portion of bits includes a same number of bits as specified by the compression level and the second portion of bits includes remaining bits in the non-residual pixel.

16. The digital system of claim 11 , wherein the means for computing a pixel residual further comprises means for spatially predicting each pixel except the non-residual pixel based on at least one neighboring pixel in the image data block.

17. The digital system of claim 16 , wherein the means for spatially predicting predicts a pixel based on a top neighboring pixel, a top left neighboring pixel, and a left neighboring pixel.

18. The digital system of claim 11 , wherein the means for computing a pixel residual further comprises means for computing a pixel residual for each pixel as a difference between a value of the pixel and a minimum pixel value in the image data block.

19. The digital system of claim 12 , further comprising:

means for storing the compressed block in a compressed data buffer in external memory; and

means for storing the compression flag in a compression flag buffer.

20. The digital system of claim 19 , further comprising means for storing the image data block in the compressed data buffer when the compression level specifies a number of bits equal to a number of bits in a pixel.