Method and apparatus for palette based coding mode under local dual tree structure

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

decoding, by a processor, prediction information of a block from a coded video bitstream;

determining, by the processor, whether to allow a palette based coding mode for the block based on a comparison of a size of the block with a threshold;

determining, by the processor, whether the block is under a local dual tree structure based on the prediction information; and

decoding, by the processor, the block based on the determination of whether to allow the palette based coding mode for the block and the determination of whether the block being under the local dual tree structure.

2. The method of claim 1 , further comprising:

disallowing the palette based coding mode for the block in response to the size of the block being smaller than the threshold.

3. The method of claim 1 , wherein the threshold is defined to disallow the local dual tree structure in response to the block being larger than the threshold.

4. The method of claim 1 , further comprising:

disallowing, the palette based coding mode for the block in response to the block being a chroma block and the size of the chroma block being smaller than the threshold.

5. The method of claim 1 , further comprising:

disallowing, the palette based coding mode for the block based on a combination of a mode type and a tree type of the block that indicates the block being a chroma block under the local dual tree structure.

6. The method of claim 1 , further comprising:

decoding, from the coded video bitstream, a flag indicating whether the palette based coding mode is used on the block in response to the palette based coding mode being allowed;

decoding the block using the palette based coding mode in response to the flag indicating a use of the palette based coding mode on the block; and

bypassing an update of a palette predictor list in response to the block being under the local dual tree structure.

7. The method of claim 6 , further comprising:

updating, in response to not triggering of the local dual tree structure, the palette predictor list based on a palette used in the decoding of the block.

8. The method of claim 1 , further comprising:

decoding, from the coded video bitstream, a flag indicating whether the palette based coding mode is used on the block in response to the palette based coding mode being allowed; and

decoding the block based on a palette having a reduced maximum size in response to the flag indicating a use of the palette based coding mode on the block and the block being under the local dual tree structure.

9. The method of claim 8 , further comprising:

updating a palette predictor list based on the palette used in the decoding of the block, a size of the palette predictor list being limited by a reduced maximum size.

10. An apparatus for video decoding, comprising:

processing circuitry configured to:

decode prediction information of a block from a coded video bitstream;

determine whether to allow a palette based coding mode for the block based on a comparison of a size of the block with a threshold;

determine whether the block is under a local dual tree structure based on the prediction information; and

decode the block based on the determination of whether to allow the palette based coding mode for the block and the determination of whether the block being under the local dual tree structure.

11. The apparatus of claim 10 , wherein the processing circuitry is configured to:

disallow, the palette based coding mode for the block in response to the size of the block being smaller than the threshold.

12. The apparatus of claim 10 , wherein the threshold is defined to disallow the local dual tree structure in response to the block being larger than the threshold.

13. The apparatus of claim 10 , wherein the processing circuitry is configured to:

disallow, the palette based coding mode for the block in response to the block being a chroma block and the size of the chroma block being smaller than the threshold.

14. The apparatus of claim 10 , wherein the processing circuitry is configured to:

disallow, the palette based coding mode for the block based on a combination of a mode type and a tree type of the block that indicates the block being a chroma block under the local dual tree structure.

15. The apparatus of claim 10 , wherein the processing circuitry is configured to:

decode, from the coded video bitstream, a flag indicating whether the palette based coding mode is used on the block in response to the palette based coding mode being allowed;

decode the block using the palette based coding mode in response to the flag indicating a use of the palette based coding mode on the block; and

bypass an update of a palette predictor list in response to the block being under the local dual tree structure.

16. The apparatus of claim 15 , wherein the processing circuitry is configured to:

update, in response to not triggering the local dual tree structure, the palette predictor list based on a palette used in the decoding of the block.

17. The apparatus of claim 10 , wherein the processing circuitry is configured to:

decode, from the coded video bitstream, a flag indicating whether the palette based coding mode is used on the block in response to the palette based coding mode being allowed; and

decode the block based on a palette having a reduced maximum size in response to the flag indicating a use of the palette based coding mode on the block and the block being under the local dual tree structure.

18. The apparatus of claim 17 , wherein the processing circuitry is configured to:

update a palette predictor list based on the palette used in the decoding of the block, a size of the palette predictor list being limited by a reduced maximum size.

19. A non-transitory computer-readable medium storing instructions which when executed by a computer for video decoding cause the computer to perform:

decoding prediction information of a block from a coded video bitstream;

determining whether to allow a palette based coding mode for the block based on a comparison of a size of the block with a threshold;

determining whether the block is under a local dual tree structure based on the prediction information; and

decoding the block based on the determination of whether to allow the palette based coding mode for the block and the determination of whether the block being under the local dual tree structure.

20. The non-transitory computer-readable medium of claim 19 , wherein the instructions cause the computer to perform:

disallowing the palette based coding mode for the block based on a combination of a mode type and a tree type of the block that indicates the block being a chroma block under the local dual tree structure.