Method for decoding a stream of coded data representative of a sequence of images and method for coding a sequence of images

1. A method comprising:

accessing coded data representative of at least a portion of an image divided into blocks;

calculating an average of a current block of said blocks from an average of a prediction block of said current block and from a DC coefficient reconstructed for said current block,

calculating a weighted prediction parameter equal to a ratio of the average of said current block and the average of said prediction block;

transforming a block of coefficients into a residual block, wherein said block of coefficients comprises a null value as DC coefficient and AC coefficients reconstructed for said current block; and

reconstructing the current block by merging said residual block and said prediction block, said prediction block being weighted by said weighted prediction parameter.

2. The method according to claim 1 , wherein calculating the average of said current block comprises weighting said average of said prediction block by a decoded initial weighted prediction parameter.

3. The method according to claim 1 , wherein calculating the average of said current block comprises weighting said average of said prediction block by an initial weighted prediction parameter equal to a ratio between an average of a neighbourhood of the current block and an average of a corresponding neighbourhood of a reference block associated with said current block.

4. A method comprising:

accessing at least a portion of an image divided into blocks;

calculating a prediction error between an average of a current block of the blocks and an average of a prediction block of said current block,

calculating a corrected average of said current block from said average of said prediction block and from the prediction error successively quantized and dequantized;

calculating a weighted prediction parameter equal to a ratio of the corrected average of said current block and the average of said prediction block;

determining a residual block by extracting from said current block said prediction block being weighted by said weighted prediction parameter, and

coding said residual block by transforming said residual block into a DC coefficient and AC coefficients, by quantizing said AC coefficients and by entropy coding the quantized prediction error and said quantized AC coefficients.

5. The method according to claim 4 , wherein, calculating said prediction error comprises weighting said average of said prediction block by an initial weighted prediction parameter and coding said initial weighted prediction parameter.

6. The method according to claim 5 , wherein, said initial weighted prediction parameter is determined for a part of the image to which said current block belongs by:

determining an average of said image part, called a first average,

determining an average of the corresponding image part to which a reference block associated with said current block belongs, called a second average, and

calculating said weighted prediction parameter as the ratio of said first average and said second average.

7. The method according to claim 6 , in which said image part is the entire image.

8. The method according to claim 6 , in which said image part is an image slice.

9. The method according to claim 4 , wherein calculating said prediction error comprises weighting said average of said prediction block by an initial weighted prediction parameter equal to a ratio between an average of a neighbourhood of the current block and an average of the corresponding neighbourhood of a reference block associated with said current block.

10. A decoding device comprising:

a memory; and

a processor coupled to the memory, the processor configured to:

access coded data representative of at least a portion of an image divided into blocks,

calculate an average of a current block, of the blocks, from an average of a prediction block of said current block and from a DC coefficient reconstructed for said current block,

calculate a weighted prediction parameter equal to a ratio of the average of said current block and the average of said prediction block,

transforming a block of coefficients into a residual block, wherein said block of coefficients comprises a null value as DC coefficient and AC coefficients reconstructed for said current block, and

reconstruct the current block by merging said residual block and said prediction block, said prediction block being weighted by said weighted prediction parameter.

11. The decoding device according to claim 10 , wherein to calculate the average of said current block comprises weighting said average of said prediction block by a decoded initial weighted prediction parameter.

12. The decoding device according to claim 10 , wherein to calculate the average of said current block comprises weighting said average of said prediction block by an initial weighted prediction parameter equal to a ratio between an average of a neighbourhood of the current block and an average of a corresponding neighbourhood of a reference block associated with said current block.

13. A coding device comprising:

a memory; and

a processor coupled to the memory, the processor configured to:

access at least a portion of an image divided into blocks;

calculate a prediction error between an average of a current block, of the blocks, and an average of a prediction block of said current block,

calculate a corrected average of said current block from said average of said prediction block and from the prediction error successively quantized and dequantized,

calculate a weighted prediction parameter equal to a ratio of the corrected average of said current block and the average of said prediction block,

determine a residual block by extracting from said current block said prediction block being weighted by said weighted prediction parameter, and

code said residual block by transforming said residual block into a DC coefficient and AC coefficients, by quantizing said AC coefficients and by entropy coding the quantized prediction error and said quantized AC coefficients.

14. The coding device according to claim 13 , wherein, to calculate said prediction error comprises weighting said average of said prediction block by an initial weighted prediction parameter and coding said initial weighted prediction parameter.

15. The coding device according to claim 14 , wherein said initial weighted prediction parameter is determined for a part of the image to which said current block belongs by:

determining an average of said image part, called a first average,

determining an average of the corresponding image part to which a reference block associated with said current block belongs, called a second average, and

calculating said weighted prediction parameter as the ratio of said first average and said second average.

16. The coding device according to claim 15 , in which said image part is the entire image.

17. The coding device according to claim 15 , in which said image part is an image slice.

18. The coding device according to claim 13 , wherein to calculate said prediction error comprises weighting said average of said prediction block by an initial weighted prediction parameter equal to a ratio between an average of a neighbourhood of the current block and an average of the corresponding neighbourhood of a reference block associated with said current block.

19. A non-transitory computer readable medium having stored thereon software that, when executed by a processor, performs:

accessing coded data representative of at least a portion of an image divided into blocks;

calculating an average of a current block, of said blocks, from an average of a prediction block of said current block and from a DC coefficient reconstructed for said current block;

calculating a weighted prediction parameter equal to a ratio of the average of said current block and the average of said prediction block;

transforming a block of coefficients into a residual block, wherein said block of coefficients comprises a null value as DC coefficient and AC coefficients reconstructed for said current block; and

reconstructing the current block by merging said residual block and said prediction block, said prediction block being weighted by said weighted prediction parameter.

20. The non-transitory computer readable medium according to claim 19 , wherein calculating the average of said current block comprises weighting said average of said prediction block by a decoded initial weighted prediction parameter.

21. The non-transitory computer readable medium according to claim 19 , wherein calculating the average of said current block comprises weighting said average of said prediction block by an initial weighted prediction parameter equal to a ratio between an average of a neighbourhood of the current block and an average of a corresponding neighbourhood of a reference block associated with said current block.

22. A non-transitory computer readable medium having stored thereon software that, when executed by a processor, performs:

accessing at least a portion of an image divided into blocks;

calculating a prediction error between an average of a current block of the blocks and an average of a prediction block of said current block,

calculating a corrected average of said current block from said average of said prediction block and from the prediction error successively quantized and dequantized;

calculating a weighted prediction parameter equal to a ratio of the corrected average of said current block and the average of said prediction block;

determining a residual block by extracting from said current block said prediction block being weighted by said weighted prediction parameter; and

coding said residual block by transforming said residual block into a DC coefficient and AC coefficients, by quantizing said AC coefficients and by entropy coding the quantized prediction error and said quantized AC coefficients.

23. The non-transitory computer readable medium according to claim 22 , wherein, calculating said prediction error comprises weighting said average of said prediction block by an initial weighted prediction parameter and coding said initial weighted prediction parameter.

24. The non-transitory computer readable medium according to claim 23 , wherein said initial weighted prediction parameter is determined for a part of the image to which said current block belongs by:

determining an average of said image part, called a first average,

determining an average of the corresponding image part to which a reference block associated with said current block belongs, called a second average, and

calculating said weighted prediction parameter as the ratio of said first average and said second average.

25. The non-transitory computer readable medium according to claim 24 , in which said image part is the entire image.

26. The non-transitory computer readable medium according to claim 24 , in which said image part is an image slice.

27. The non-transitory computer readable medium according to claim 22 , wherein calculating said prediction error comprises weighting said average of said prediction block by an initial weighted prediction parameter equal to a ratio between an average of a neighbourhood of the current block and an average of the corresponding neighbourhood of a reference block associated with said current block.