Restriction on applicability of cross component mode
A method for visual media processing, including performing a conversion between a current chroma chroma block of visual media data and a bitstream representation of the current chroma chroma block, wherein, during the conversion, a chroma residual of the current chroma chroma block is scaled based on a scaling coefficient, wherein the scaling coefficient is derived at least based on luma samples located in predefined positions.
1. A method of processing video data, comprising:
determining, for a conversion between a chroma block of a video and a bitstream of the video, whether to enable or disable a cross-component linear model intra prediction on the chroma block, based on whether one or more luma video units which cover at least one sample of a corresponding luma region of the chroma block are coded with a subblock-based prediction mode, wherein the chroma block is in a dual tree structure in which a luma component and at least one chroma component have separate partition tree structures;
in response to the cross-component linear model intra prediction enabled, determining parameters of the cross-component linear model at least based on neighboring chroma samples of the chroma block;
applying the cross-component linear model to derive prediction values of the chroma block based on the parameters; and
performing the conversion based on the prediction values, wherein the parameters of the cross-component linear model are derived by following:
checking an availability of one or more neighboring chroma blocks of the chroma block;
finding R chroma samples from neighboring chroma samples in the one or more neighboring chroma blocks to determine the parameters of the cross-component linear model, wherein R is an integer greater than 2 , and wherein at least one neighboring chroma sample does not belong to the R chroma samples based on a size of the chroma block.
2. The method of claim 1 , wherein the subblock-based prediction mode corresponds to an intra sub-partitions mode.
3. The method of claim 1 , wherein the cross-component linear model is disabled in response to the one or more luma video units being coded with the subblock- based prediction mode.
4. The method of claim 1 , wherein whether to enable or disable the cross-component linear model intra prediction on the chroma block is further based on partition information of the one or more luma video units.
5. The method of claim 4 , wherein the partition information includes a partition tree depth of the one or more luma video units.
6. The method of claim 5 , wherein the partition tree depth is a quadtree depth.
7. The method of claim 1 , wherein whether to enable or disable the cross-component linear model intra prediction on the chroma block is further based on a block dimension of one or more chroma video units which cover at least one sample of a corresponding chroma region of the chroma block.
8. The method of claim 1 , wherein whether to enable or disable the cross-component linear model intra prediction on the chroma block is further based on whether the one or more luma video units are split from multi-type partition tree operation different from a quadtree partition operation.
9. The method of claim 1 , wherein in response to the one or more neighboring chroma blocks being unavailable, the prediction values of the chroma block are set to 1<<(bitDepth−1), where bitDepth is a bit depth of the video.
10. The method of claim 1 , wherein the conversion includes encoding the chroma block into the bitstream.
11. The method of claim 1 , wherein the conversion includes decoding the chroma block from the bitstream.
12. An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:
determine, for a conversion between a chroma block of a video and a bitstream of the video, whether to enable or disable a cross-component linear model intra prediction on the chroma block, based on whether one or more luma video units which cover at least one sample of a corresponding luma region of the chroma block are coded with a subblock-based prediction mode, wherein the chroma block is in a dual tree structure in which a luma component and at least one chroma component have separate partition tree structures;
in response to the cross-component linear model intra prediction enabled, determine parameters of the cross-component linear model at least based on neighboring chroma samples of the chroma block;
apply the cross-component linear model to derive prediction values of the chroma block based on the parameters; and
perform the conversion based on the prediction values,
wherein the parameters of the cross-component linear model are derived by following:
checking an availability of one or more neighboring chroma blocks of the chroma block:
finding R chroma samples from neighboring chroma samples in the one or more neighboring chroma blocks to determine the parameters of the cross-component linear model, wherein R is an integer greater than 2, and
wherein at least one neighboring chroma sample does not belong to the R chroma samples based on a size of the chroma block.
13. The apparatus of claim 12 , wherein the subblock-based prediction mode corresponds to an intra sub-partitions mode.
14. The apparatus of claim 12 , wherein whether to enable or disable the cross-component linear model intra prediction on the chroma block is further based on partition information of the one or more luma video units, the partition information includes a partition tree depth of the one or more luma video units, and the partition tree depth is a quadtree depth.
15. The apparatus of claim 12 , wherein in response to the one or more neighboring chroma blocks being unavailable, the prediction values of the chroma block are set to 1<<(bitDepth−1), where bitDepth is a bit depth of the video.
16. A non-transitory computer-readable storage medium storing instructions that cause a processor to:
determine, for a conversion between a chroma block of a video and a bitstream of the video, whether to enable or disable a cross-component linear model intra prediction on the chroma block, based on whether one or more luma video units which cover at least one sample of a corresponding luma region of the chroma block are coded with a subblock-based prediction mode, wherein the chroma block is in a dual tree structure in which a luma component and at least one chroma component have separate partition tree structures;
in response to the cross-component linear model intra prediction enabled, determine parameters of the cross-component linear model at least based on neighboring chroma samples of the chroma block;
apply the cross-component linear model to derive prediction values of the chroma block based on the parameters; and
perform the conversion based on the prediction values,
wherein the parameters of the cross-component linear model are derived by following:
checking an availability of one or more neighboring chroma blocks of the chroma block:
finding R chroma samples from neighboring chroma samples in the one or more neighboring chroma blocks to determine the parameters of the cross-component linear model, wherein R is an integer greater than 2, and
wherein at least one neighboring chroma sample does not belong to the R chroma samples based on a size of the chroma block.
17. The non-transitory computer-readable storage medium of claim 16 , wherein the subblock-based prediction mode corresponds to an intra sub-partitions mode.
18. The non-transitory computer-readable storage medium of claim 16 , wherein whether to enable or disable the cross-component linear model intra prediction on the chroma block is further based on partition information of the one or more luma video units, the partition information includes a partition tree depth of the one or more luma video units, and the partition tree depth is a quadtree depth.
19. A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises:
determining, whether to enable or disable a cross-component linear model intra prediction on a chroma block of a video, based on whether one or more luma video units which cover at least one sample of a corresponding luma region of the chroma block are coded with a subblock-based prediction mode, wherein the chroma block is in a dual tree structure in which a luma component and at least one chroma component have separate partition tree structures;
in response to the cross-component linear model intra prediction enabled, determining parameters of the cross-component linear model at least based on neighboring chroma samples of the chroma block;
applying the cross-component linear model to derive prediction values of the chroma block based on the parameters; and
generating the bitstream of the video based on the determining,
wherein the parameters of the cross-component linear model are derived by following:
checking an availability of one or more neighboring chroma blocks of the chroma block;
finding R chroma samples from neighboring chroma samples in the one or more neighboring chroma blocks to determine the parameters of the cross-component linear model, wherein R is an integer greater than 2, and
wherein at least one neighboring chroma sample does not belong to the R chroma samples based on a size of the chroma block.
20. The non-transitory computer-readable recording medium of claim 19 , wherein the subblock-based prediction mode corresponds to an intra sub-partitions mode, and whether to enable or disable the cross-component linear model intra prediction on the chroma block is further based on partition information of the one or more luma video units, the partition information includes a partition tree depth of the one or more luma video units, and the partition tree depth is a quadtree depth.