Data decompression and packing

1. A method of data decompression comprising:

receiving compressed image data substantially in raster scan order;

determining a number of bits of compressed data that corresponds to one row of pixels of said image;

using the number of bits to pass pixel data corresponding to the row of pixels to decoding hardware; and

for each group of pixels in the row, identifying a block-based decoding scheme for the group of pixels and decoding the compressed data corresponding to the group of pixels at the decoding hardware using the identified scheme.

2. The method according to claim 1 , wherein for an even row in a part-block, the compressed data comprises all the pixel data required to output two decompressed output pixels and for a subset of the encoding patterns additionally comprises advance data for use in decompressing a pair of pixels in a subsequent row of the same part-block.

3. The method according to claim 1 , each group of pixels comprising a pair of adjacent pixels and wherein the encoded data for each pixel or pair of adjacent pixels comprises a sequence of a multiple of P bits, where P is an integer.

4. The method according to claim 1 , wherein the compressed image data comprises a block of compressed image data and the block of compressed image data comprises:

a block of compressed pixel data; and

a block of control data,

and wherein the method comprises determining a number of bits of compressed data that corresponds to one row of pixels using the block of control data.

5. The method according to claim 4 , wherein the method comprises identifying a block-based decoding scheme for the group of pixels based on control bits in the block of control data or control bits within the compressed pixel data.

6. The method according to claim 1 , wherein the method comprises decoding a plurality of groups of pixels substantially in parallel.

7. Data decompression hardware comprising:

an input for receiving compressed image data substantially in raster scan order;

control hardware arranged to determine a number of bits of compressed data that corresponds to one row of pixels of said image;

unpacking hardware arranged to use the number of bits to pass pixel data corresponding to the row of pixels to decoding hardware; and

decoding hardware arranged to decode groups of pixels from the pixel data passed from the unpacking hardware,

wherein either the control hardware or the decoding hardware is further arranged, for each group of pixels in the row, to identify a block-based decoding scheme for the group of pixels and wherein the decoding hardware is arranged, for each group of pixels, to decode compressed data corresponding to the group of pixels using the identified scheme.

8. Data decompression hardware according to claim 7 , wherein for an even row in a part-block, the compressed data comprises all the pixel data required to output two decompressed output pixels and for a subset of the encoding patterns additionally comprises advance data for use in decompressing a pair of pixels in a subsequent row of the same part-block.

9. Data decompression hardware according to claim 7 , wherein compressed image data comprises a block of compressed image data and the block of compressed image data comprises:

a block of compressed pixel data; and

a block of control data.

10. Data decompression hardware according to claim 9 , further comprising:

unpacking hardware arranged to pass the block of control data to the control hardware, and

wherein the control hardware is arranged to determine a number of bits of compressed data that corresponds to one row of pixels in a block of uncompressed image data by analysing the control data.

11. Data decompression hardware according to claim 10 , wherein:

the control hardware is further arranged to communicate the number of bits to the unpacking hardware; and

the unpacking hardware is further arranged to pass pixel data corresponding to a row of pixels to the decoding hardware.

12. Data decompression hardware according to claim 9 , wherein the control hardware is arranged, for each group of pixels in the row, to identify a block-based decoding scheme for the group of pixels based on the block of control data.

13. Data decompression hardware according to claim 9 , wherein the decoding hardware is arranged, for each group of pixels in the row, to identify a block-based decoding scheme for the group of pixels based on control bits embedded within the compressed pixel data and optionally based on data provided by the control hardware.

14. Data decompression hardware according to claim 13 , wherein the control hardware is further arranged to extract information from the block of control data identifying positions of any embedded control bits within the compressed pixel data and to provide information identifying the positions of any embedded control bits within the compressed pixel data to the decoding hardware.

15. Data decompression hardware according to claim 7 , wherein the decoding hardware comprises a plurality of decoding units, each decoding unit arranged to operate in parallel on a different group of bits within a row of pixels.

16. Data decompression hardware according to claim 7 , wherein the compressed data for each group of pixels in a row comprises a multiple of P bits, where P is an integer.

17. Data decompression hardware according to claim 16 , wherein the compressed data for each group of pixels in a row comprises one or two encoded pixel values.

18. Data decompression hardware according to claim 17 , wherein each encoded pixel value is either an encoded input pixel value or an encoded average of two input pixel values.

19. Data decompression hardware according to claim 7 , wherein the decoding hardware is arranged to output decompressed pixel data in raster scan order.

20. Data decompression hardware according to claim 7 , wherein the hardware is implemented without any buffering for the compressed pixel data.