Transform selection in a video encoder and/or video decoder
A process for selecting a transform set for a prediction block. The process can be used in both an encoder and a decoder. For example, the process can be used in both an encoder and a decoder for a prediction block that has been predicted from a reference block. In some embodiments, both the prediction block and the reference block are intra blocks.
1. A method for encoding a video sequence comprising a plurality of pictures, the method comprising:
determining an intra prediction mode for a reference block from which a first prediction block is generated;
selecting an index to which the determined intra prediction mode is mapped;
deriving a transformation matrix based on the selected index to which the determined intra prediction mode is mapped; and
deriving transformed samples using the transformation matrix and a set of transform coefficients.
2. A method for decoding a video sequence comprising a plurality of pictures, the method comprising:
determining an intra prediction mode for a reference block from which a first prediction block is generated;
selecting an index to which the determined intra prediction mode is mapped;
deriving a transformation matrix based on the selected index to which the determined intra prediction mode is mapped; and
deriving transformed samples using the transformation matrix and a set of transform coefficients.
3. The method of claim 2 , wherein the reference block is coded using an intra prediction mode.
4. The method of claim 2 , wherein
the first prediction block belongs to a chroma color component,
the reference block belongs to a luma color component, and
the method further comprises generating the first prediction block using the reference block and a cross-component linear model (CCLM) prediction mode.
5. The method of claim 2 , wherein the first prediction block belongs to a color component and the reference block belongs to the same color component.
6. The method of claim 5 , further comprises generating the first prediction block using the reference block and an intra block copy (IBC) tool.
7. The method of claim 1 , further comprising determining that a set of conditions is satisfied, wherein the step of deriving the transformed samples is performed as a result of determining that the set of conditions is satisfied.
8. The method of claim 2 , further comprising determining that a set of conditions is satisfied, wherein the step of deriving the transformed samples is performed as a result of determining that the set of conditions is satisfied.
9. The method of claim 7 , wherein determining that the set of conditions is satisfied comprises:
determining the number of non-zero transform coefficients (N) of the reference block; and
determining that N satisfies a certain condition.
10. The method of claim 7 , wherein determining that the set of conditions is satisfied comprises:
determining a quantization parameter (QP) used for the reference block; and
determining that the QP satisfies a certain condition.
11. The method of claim 8 , wherein determining that the set of conditions is satisfied comprises determining that a particular flag received from an encoder is set to a certain value.
12. The method of claim 1 , wherein deriving the transformed samples comprises transforming a residual block using the transformation matrix.
13. The method of claim 1 , wherein deriving the transformed samples comprises using a primary transform unit to transform a residual block.
14. The method of claim 2 , wherein deriving the transformed samples comprises inverse transforming a coefficient block after dequantization.
15. The method of claim 2 , wherein deriving the transformed samples comprises
inverse transforming a coefficient block.
16. A non-transitory computer readable medium which includes a computer program, the computer program comprising instructions which, when executed by processing circuity, cause the processing circuity to carry out the method of claim 1 .
17. A non-transitory computer readable medium which includes a computer program, the computer program comprising instructions which, when executed by processing circuity, cause the processing circuity to carry out the method of claim 2 .
18. An encoder for encoding a video sequence comprising a plurality of pictures, the encoder being adapted to:
determine an intra prediction mode for a reference block from which a first prediction block is generated;
select an index to which the determined intra prediction mode is mapped;
deriving a transformation matrix based on the selected index to which the determined intra prediction mode is mapped; and
deriving transformed samples using the transformation matrix and a set of transform coefficients.
19. A decoder for decoding a video sequence comprising a plurality of pictures, the decoder being adapted to:
determine an intra prediction mode for a reference block from which a first prediction block is generated;
select an index to which the determined intra prediction mode is mapped;
deriving a transformation matrix based on the selected index to which the determined intra prediction mode is mapped; and
deriving transformed samples using the transformation matrix and a set of transform coefficients.