Method and apparatus for video coding

1. A method for video decoding in a decoder, comprising:

decoding prediction information for a current block in a current picture that is a part of a coded video sequence, the prediction information indicating a partition type and a block size for the current block;

creating a local partition tree for a small chroma intra prediction unit (SCIPU) region in a single partition tree, a tree depth of the local partition tree for the SCIPU region being based on a threshold and whether the SCIPU region is inter coded;

determining whether the current block is a parent node of the local partition tree based on the partition type and the block size of the current block;

partitioning the current block according to the local partition tree in response to the current block being the parent node of the local partition tree; and

reconstructing the current block based on a prediction mode of the current block.

2. The method of claim 1 , wherein the prediction mode of the current block is determined to be a non-inter prediction mode based on (i) the block size being 64 samples and the local partition tree being a quad tree, or (ii) the block size being 64 samples and the local partition tree being a ternary tree, or (iii) the block size being 32 samples and the local partition tree being a binary tree.

3. The method of claim 1 , wherein the prediction mode of the current block is determined based on a signaled flag included in the prediction information and (i) the block size being 64 samples and the local partition tree being a binary tree or (ii) the block size being 128 samples and the local partition tree being a ternary tree.

4. The method of claim 1 , wherein the threshold is a first threshold based on the current block being inter coded and a second threshold based on the current block being non-inter coded, the first threshold being less than the second threshold.

5. The method of claim 1 , further comprising:

determining the current block to be a SCIPU based on the current block being the parent node of the local partition tree.

6. The method of claim 1 , wherein the partitioning further comprises:

partitioning the current block based on whether the prediction mode of the current block is determined.

7. The method of claim 1 , wherein the partitioning further comprises:

partitioning the current block based on whether the current block is inter coded.

8. A method for video decoding in a decoder, comprising:

decoding prediction information for a current block in a current picture that is a part of a coded video sequence, the prediction information indicating a partition tree structure for chroma samples of the current block;

partitioning the chroma samples of the current block into a plurality of sub-blocks based on the partition tree structure;

determining whether at least one of an above neighboring sample and a left neighboring sample of a sub-block in the plurality of sub-blocks is unavailable based on an availability marking of the at least one above neighboring sample and the left neighboring sample in a parallel-processable region (PPR);

predicting the chroma samples of the sub-block in the plurality of sub-blocks based on a subset of chroma intra prediction modes in response to (i) at least one of the above neighboring sample and the left neighboring sample of the sub-block being unavailable for predicting the sub-block, and (ii) a block size of the sub-block being less than or equal to a size threshold or a side length of the sub-block being less than or equal to a length threshold; and

reconstructing the current block based on the predicted chroma samples.

9. The method of claim 8 , wherein a block size of the current block is larger than the size threshold and the block size of the sub-block being less than or equal to the size threshold, or a side length of the current block is larger than the length threshold and the side length of the sub-block being less than or equal to the length threshold.

10. The method of claim 8 , wherein the size threshold includes one of 2×2, 2×4, 4×2, and a block size of an allowed smallest luma intra coded block, and the length threshold includes one of 2, 4, and a side length of the allowed smallest luma intra coded block.

11. The method of claim 8 , wherein the chroma intra prediction modes includes planar mode, DC mode, horizontal mode, vertical mode, a derived mode (DM), a left cross-component linear mode (L_CCLM), a top cross-component linear mode (T_CCLM), and a left and top cross-component linear mode (LT_CCLM).

12. The method of claim 8 , wherein the subset of the chroma intra prediction modes includes one or two of the chroma intra prediction modes.

13. The method of claim 8 , wherein the subset of the chroma intra prediction modes includes at least one of a derived mode (DM), a left cross-component linear mode (L_CCLM), and a vertical mode, based on the above neighboring sample of the sub-block being unavailable for predicting the sub-block and located within the current block.

14. The method of claim 8 , wherein the subset of the chroma intra prediction modes includes at least one of a derived mode (DM), a top cross-component linear mode (T_CCLM), and a horizontal mode, based on the left neighboring sample of the sub-block being unavailable for predicting the sub-block and located within the current block.

15. The method of claim 8 , wherein the current block is included within the PPR in which all the sub-blocks are reconstructed in parallel.

16. An apparatus, comprising processing circuitry configured to:

decode prediction information for a current block in a current picture that is a part of a coded video sequence, the prediction information indicating a partition type and a block size for the current block;

create a local partition tree for a small chroma intra prediction unit (SCIPU) region in a single partition tree, a tree depth of the local partition tree for the SCIPU region being based on a threshold and whether the SCIPU region is inter coded;

determine whether the current block is a parent node of the local partition tree based on the partition type and the block size of the current block;

partition the current block according to the local partition tree in response to the current block being the parent node of the local partition tree; and

reconstruct the current block based on a prediction mode of the current block.

17. The apparatus of claim 16 , wherein the processing circuitry is further configured to at least one of:

partition the current block based on whether the prediction mode of the current block is determined; and

partition the current block based on whether the current block is inter coded.

18. An apparatus, comprising processing circuitry configured to:

decode prediction information for a current block in a current picture that is a part of a coded video sequence, the prediction information indicating a partition tree structure for chroma samples of the current block;

partition the chroma samples of the current block into a plurality of sub-blocks based on the partition tree structure;

determine whether at least one of an above neighboring sample and a left neighboring sample of a sub-block in the plurality of sub-blocks is unavailable based on an availability marking of the at least one above neighboring sample and the left neighboring sample in a parallel-processable region (PPR);

predict the chroma samples of the sub-block in the plurality of sub-blocks based on a subset of chroma intra prediction modes in response to (i) at least one of the above neighboring sample and the left neighboring sample of the sub-block being unavailable for predicting the sub-block, and (ii) a block size of the sub-block being less than or equal to a size threshold or a side length of the sub-block being less than or equal to a length threshold; and

reconstruct the current block based on the predicted chroma samples.

19. A non-transitory computer-readable storage medium storing a program executable by at least one processor to perform:

decoding prediction information for a current block in a current picture that is a part of a coded video sequence, the prediction information indicating a partition type and a block size for the current block;

creating a local partition tree for a small chroma intra prediction unit (SCIPU) region in a single partition tree, a tree depth of the local partition tree for the SCIPU region being based on a threshold and whether the SCIPU region is inter coded;

determining whether the current block is a parent node of the local partition tree based on the partition type and the block size of the current block;

partitioning the current block according to the local partition tree in response to the current block being the parent node of the local partition tree; and

reconstructing the current block based on a prediction mode of the current block.

20. A non-transitory computer-readable storage medium storing a program executable by at least one processor to perform:

decoding prediction information for a current block in a current picture that is a part of a coded video sequence, the prediction information indicating a partition tree structure for chroma samples of the current block;

partitioning the chroma samples of the current block into a plurality of sub-blocks based on the partition tree structure;

determining whether at least one of an above neighboring sample and a left neighboring sample of a sub-block in the plurality of sub-blocks is unavailable based on an availability marking of the at least one above neighboring sample and the left neighboring sample in a parallel-processable region (PPR);

predicting the chroma samples of the sub-block in the plurality of sub-blocks based on a subset of chroma intra prediction modes in response to (i) at least one of the above neighboring sample and the left neighboring sample of the sub-block being unavailable for predicting the sub-block, and (ii) a block size of the sub-block being less than or equal to a size threshold or a side length of the sub-block being less than or equal to a length threshold; and

reconstructing the current block based on the predicted chroma samples.