Palette mode for local dual tree

1. A method of processing video data, comprising:

determining, for a conversion between a first video block of a video and a bitstream of the video, that a first prediction mode is applied to the first video block;

maintaining a predictor palette table;

constructing, in the first prediction mode, a first palette comprising one or more palette predictors for the first video block based on the predictor palette table; and

performing the conversion based on the first prediction mode,

wherein in the first prediction mode, reconstructed samples of the first video block are represented by a set of representative color values, and the set of representative color values comprises at least one of 1) palette predictors derived from the first palette, 2) escaped samples, or 3) palette information included in the bitstream,

wherein a maximum number of entries in the first palette is based on a tree type of the first video block,

wherein the first prediction mode is applied to a second video block of the video, and a second palette for the second video block is constructed based on the predictor palette table, and

wherein in a case that a single tree is applied to the first video block and a local dual tree is applied to the second video block, the maximum number of entries in the second palette is half of the maximum number of entries in the first palette.

2. The method of claim 1 , wherein the predictor palette table is updated based on the first palette.

3. The method of claim 1 , wherein the second video block is a luma block, and the second video block has a tree type not equal to single tree and has a slice type not equal to I slice.

4. The method of claim 1 , wherein the second video block is a luma block, and the second video block is obtained by splitting a luma parent block of a coding tree node, wherein a chroma parent block of the coding tree node is disallowed to be split.

5. The method of claim 4 , wherein the first video block is a luma block, and a palette size of a chroma block corresponding to the first video block is greater than a palette size of the chroma parent block.

6. The method of claim 4 , wherein the second palette has a size greater than a palette size of the chroma parent block.

7. The method of claim 1 , wherein the first prediction mode is applied to a second video block of the video, and a second palette for the second video block is constructed based on the predictor palette table; and

wherein in case that a dual tree is applied to the first video block and a local dual tree is applied to the second video block, the maximum number of entries in the predictor palette table is different for the first video block and the second video block.

8. The method of claim 7 , wherein the first video block is a chroma block,

wherein the second video block is a luma block, and the second video block is obtained by splitting a luma parent block of a coding tree node, wherein a chroma parent block of the coding tree node is disallowed to be split, and

wherein a size of the first palette is greater than a palette size of the chroma parent block.

9. The method of claim 1 , wherein the conversion includes encoding the video into the bitstream.

10. The method of claim 1 , wherein the conversion includes decoding the video from the bitstream.

11. 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 first video block of a video and a bitstream of the video, that a first prediction mode is applied to the first video block;

maintain a predictor palette table;

construct, in the first prediction mode, a first palette comprising one or more palette predictors for the first video block based on the predictor palette table; and

perform the conversion based on the first prediction mode,

wherein in the first prediction mode, reconstructed samples of the first video block are represented by a set of representative color values, and the set of representative color values comprises at least one of 1) palette predictors derived from the first palette, 2) escaped samples, or 3) palette information included in the bitstream,

wherein a maximum number of entries in the first palette is based on a tree type of the first video block,

wherein the first prediction mode is applied to a second video block of the video, and a second palette for the second video block is constructed based on the predictor palette table, and

wherein in a case that a single tree is applied to the first video block and a local dual tree is applied to the second video block, the maximum number of entries in the second palette is half of the maximum number of entries in the first palette.

12. A non-transitory computer-readable storage medium storing instructions that cause a processor to:

determine, for a conversion between a first video block of a video and a bitstream of the video, that a first prediction mode is applied to the first video block;

maintain a predictor palette table;

construct, in the first prediction mode, a first palette comprising one or more palette predictors for the first video block based on the predictor palette table; and

perform the conversion based on the first prediction mode,

wherein in the first prediction mode, reconstructed samples of the first video block are represented by a set of representative color values, and the set of representative color values comprises at least one of 1) palette predictors derived from the first palette, 2) escaped samples, or 3) palette information included in the bitstream,

wherein a maximum number of entries in the first palette is based on a tree type of the first video block,

wherein the first prediction mode is applied to a second video block of the video, and a second palette for the second video block is constructed based on the predictor palette table, and

wherein in a case that a single tree is applied to the first video block and a local dual tree is applied to the second video block, the maximum number of entries in the second palette is half of the maximum number of entries in the first palette.

13. 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, for a first video block of a video, that a first prediction mode is applied to the first video block;

maintaining a predictor palette table;

constructing, in the first prediction mode, a first palette comprising one or more palette predictors for the first video block based on the predictor palette table; and

generating a bitstream of the video based on the first prediction mode,

wherein in the first prediction mode, reconstructed samples of the first video block are represented by a set of representative color values, and the set of representative color values comprises at least one of 1) palette predictors derived from the first palette, 2) escaped samples, or 3) palette information included in the bitstream,

wherein a maximum number of entries in the first palette is based on a tree type of the first video block,

wherein the first prediction mode is applied to a second video block of the video, and a second palette for the second video block is constructed based on the predictor palette table, and

wherein in a case that a single tree is applied to the first video block and a local dual tree is applied to the second video block, the maximum number of entries in the second palette is half of the maximum number of entries in the first palette.

14. The apparatus of claim 11 , wherein the second video block is a luma block, and the second video block has a tree type not equal to single tree and has a slice type not equal to I slice.

15. The apparatus of claim 11 , wherein the second video block is a luma block, and the second video block is obtained by splitting a luma parent block of a coding tree node, wherein a chroma parent block of the coding tree node is disallowed to be split.

16. The apparatus of claim 15 , wherein the first video block is a luma block, and a palette size of a chroma block corresponding to the first video block is greater than a palette size of the chroma parent block.

17. The apparatus of claim 15 , wherein the second palette has a size greater than a palette size of the chroma parent block.

18. The non-transitory computer-readable storage medium of claim 12 , wherein the predictor palette table is updated based on the first palette.

19. The non-transitory computer-readable storage medium of claim 12 , wherein the second video block is a luma block, and the second video block has a tree type not equal to single tree and has a slice type not equal to I slice.

20. The non-transitory computer-readable recording medium of claim 13 , wherein the predictor palette table is updated based on the first palette.