Derivation of quantization matrices for joint Cb-Br coding
A method for reconstructing a block of an image, said block comprising a plurality of components and being predictively encoded from a reference block, includes if a single quantized residual block is used to jointly encode at least two components of the plurality of components, deriving at least one quantization matrix from a plurality of scaling lists each defined for one component of the plurality of components; and, applying one of the at least one derived quantization matrix to the single quantized residual block to obtain a reconstructed residual block for each of the at least two components.
1. A method for reconstructing a block of an image, the method comprising:
determining that one single residual block is signaled for both a first chroma component of the block and a second chroma component of the block different from the first chroma component;
responsive to the determining, deriving a quantization matrix by mixing a first scaling list associated with the first chroma compenent and a second scaling list associated with the second chroma component or by mixing first and second scaling factor matrices derived from the first and second scaling lists respectively; and
applying the derived quantization matrix to the single residual block to obtain a reconstructed residual block for each of the first and second chroma components.
2. The method of claim 1 , wherein the first scaling factor matrix is derived from thefirst scaling list associated with the first chroma component and the second scaling factor matrix is derived from the second scaling list associated with the second chroma component.
3. The method of claim 1 , wherein mixing the first and second scaling factor matrices comprises applying a function to the first and second scaling factor matrices, the function being representative of an average or a weighted average of the first and second scaling factor matrices and wherein mixing the first and second scaling lists comprises applying a function to the first and second scaling lists, the function being representative of an average or a weighted average of the first and second scaling lists.
4. The method of claim 2 , comprising decoding the first scaling list and the second scaling list from a bitstream representative of the image.
5. The method of claim 1 , comprising decoding a syntax element indicating if the quantization matrix applied to the single residual block is derived by mixing the first and second scaling factor matrices or the first and second scaling lists or is equal to one scaling list or one scaling factor matrix associated with one component among of the first and second chroma components.
6. A device for reconstructing a block of an image, the device comprising one or more processors and at least one memory coupled to the one or more processors, wherein the one or more processors are configured to perform:
determining that one single residual block is signaled for both a first chroma component of the block and a second chroma component of the block different from the first chroma component;
responsive to the determining deriving a quantization matrix by mixing a first scaling list associated with the first chroma component and a second scaling list associated with the second chroma component or by mixing first and second scaling matrices; and
applying the derived quantization matrix to the single residual block to obtain a reconstructed residual block for each of the first and second chroma components.
7. The device of claim 6 , wherein the first scaling factor matrix is derived from the first scaling list associated with the first chroma component and the second scaling factor matrix is derived from the second scaling list associated with the second chroma component.
8. The device of claim 6 , wherein mixing the first and second scaling factor matrices comprises applying a function to the first and second scaling factor matrices, the function being representative of an average or a weighted average of the first and second scaling factor matrices and wherein mixing the first and second lists comprises applying a function to the first and second scaling lists, the function being representative of an average or a weighted average of the first and second scaling lists.
9. The device of claim 7 , wherein the one or more processors are configured to perform decoding the first scaling list and the second scaling list from a bitstream representative of the image.
10. The device of claim 6 , wherein the one or more processors are configured to perform decoding a syntax element indicating if the quantization matrix applied to the single residual block is derived by mixing the first and second scaling factor matrices or the first and second scaling lists or is equal to one scaling list or one scaling factor matrix associated with one component among the first and second chroma components.
11. A method for encoding a block of an image, the method comprising:
determining that one single residual block is signaled for both a first chroma component of the block and a second chroma component of the block different from the first chroma component;
responsive to the determining deriving a quantization matrix by mixing a first scaling list associated with the first chroma component and a second scaling list associated with the second chroma component or by mixing first and second scaling factor matrices derived from the first and second scaling lists respectively; and
applying the derived quantization matrix to the single residual block to obtain a reconstructed residual block for each of the first and second chroma components.
12. The method of claim 11 , wherein the first scaling factor matrix is derived from the first scaling list associated with the first chroma component and the second scaling factor matrix is derived from the second scaling list associated with the second chroma component.
13. The method of claim 11 , wherein mixing the first and second scaling factor matrices comprises applying a function to the first and second scaling factor matrices, the function being representative of an average or a weighted average of the first and second scaling factor matrices and wherein mixing the first and second scaling lists comprises applying a function to the first and second scaling lists, the function being representative of an average or a weighted average of the first and second scaling lists.
14. The method of claim 12 , comprising encoding the first scaling list and the second scaling list in a bitstream representative of the image.
15. The method of claim 11 , comprising encoding a syntax element indicating if the quantization matrix applied to the single residual block is derived by mixing the first and second scaling factor matrices or the first and second scaling lists or is equal to one scaling list or one scaling factor matrix associated with one component among the first and second chroma components.
16. A device for encoding a block of an image, the device comprising one or more processors and at least one memory coupled to the one or more processors, wherein the one or more processors are configured to perform:
determining that one single residual block is signaled for both a first chroma component of the block and a second chroma component of the block different from the first chroma component;
responsive to the determining, obtaining a first scaling factor matrix associated with the first chroma component and a second scaling factor matrix associated with the second chroma component;
deriving a quantization matrix by mixing a first scaling list associated with the first chroma component and a second scaling list associated with the second chroma component or by mixing first and second scaling factor matrices derived from the first and second scaling lists respectively; and
applying the derived quantization matrix to the single residual block to obtain a reconstructed residual block for each of the first and second chroma components.
17. The device of claim 16 , wherein the first scaling factor matrix is derived from the first scaling list associated with the first chroma component and the second scaling factor matrix is derived from the second scaling list associated with the second chroma component.
18. The device of claim 16 , wherein mixing the first and second scaling factor matrices comprises applying a function to the first and second scaling factor matrices, the function being representative of an average or a weighted average of the first and second scaling factor matrices and wherein mixing the first and second scaling lists comprises applying a function to the first and second scaling lists, the function being representative of an average or a weighted average of the first and second scaling lists.
19. The device of claim 17 , wherein the one or more processors are configured to perform encoding the first scaling list and the second scaling list in a bitstream representative of the image.
20. The device of claim 16 , wherein the one or more processors are configured to perform encoding a syntax element indicating if the quantization matrix applied to the single residual block is derived by mixing the first and second scaling factor matrices or the first and second scaling lists or is equal to one scaling list or one scaling factor matrix associated with one component among the first and second chroma components.