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 decoding a video sequence comprising a plurality of pictures, the method comprising:
obtaining an intra prediction mode value (predModeIntra) specifying an intra prediction mode;
using the obtained intra prediction mode value to select an index value (lfnstTrSetIdx) from a set of index values;
deriving a transformation matrix based on the index value selected using the obtained intra prediction mode value;
obtaining an array of transform coefficients; and
deriving transformed samples using the transformation matrix and the array of transform coefficients.
2. The method of claim 1 , wherein deriving a transformation matrix based on the index value comprises using the index value to select a transformation matrix from a set of two or more transformation matrices.
3. The method of claim 1 , wherein
the obtained intra prediction mode value is associated with a first two-dimensional matrix of sample values (pY), and
the method further comprises generating a second two-dimensional matrix of sample values (predSamples) using pY.
4. The method of claim 3 , wherein
pY is a two-dimensional matrix of luma sample values, and
predSamples is a two-dimensional matrix of chroma sample values.
5. The method of claim 4 , wherein generating predSamples using pY comprises using a cross-component linear model (CCLM) prediction mode to generate predSamples.
6. 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.
7. The method of claim 6 , 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.
8. The method of claim 1 , wherein deriving the transformed samples comprises inverse transforming a coefficient block after dequantization.
9. The method of claim 1 , wherein deriving the transformed samples comprises inverse transforming a coefficient block.
10. A non-transitory computer readable medium storing a computer program, the computer program comprising instructions which, when executed by processing circuitry of a decoder, causes the decoder to perform the method of claim 1 .
11. A decoder for decoding a video sequence comprising a plurality of pictures, the decoder comprising:
memory; and
processing circuitry coupled to the memory, wherein the decoder is configured to perform a process that comprises:
obtaining an intra prediction mode value (predModeIntra) specifying an intra prediction mode;
using the obtained intra prediction mode value to select an index value (lfnstTrSetIdx) from a set of index values;
deriving a transformation matrix based on the index value selected using the obtained intra prediction mode value;
obtaining an array of transform coefficients; and
deriving transformed samples using the transformation matrix and the array of transform coefficients.
12. The decoder of claim 11 , wherein deriving a transformation matrix based on the index value comprises using the index value to select a transformation matrix from a set of two or more transformation matrices.
13. The decoder of claim 11 , wherein
the obtained intra prediction mode value is associated with a first two-dimensional matrix of sample values (pY), and
the process further comprises generating a second two-dimensional matrix of sample values (predSamples) using pY.
14. The decoder of claim 13 , wherein
pY is a two-dimensional matrix of luma sample values, and
predSamples is a two-dimensional matrix of chroma sample values.
15. The decoder of claim 14 , wherein generating predSamples using pY comprises using a cross-component linear model (CCLM) prediction mode to generate predSamples.
16. The decoder of claim 11 , wherein the process further comprises 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.
17. The decoder of claim 16 , 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.
18. The decoder of claim 11 , wherein deriving the transformed samples comprises inverse transforming a coefficient block after dequantization.
19. The decoder of claim 11 , wherein deriving the transformed samples comprises inverse transforming a coefficient block.