Method and apparatus for video coding

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

decoding prediction information of a current block from a coded video bitstream, the prediction information being indicative of an intra prediction mode;

determining whether the current block meets a block size condition that limits an application of a position dependent intra prediction combination (PDPC) in a reconstruction of the current block based on a size of the current block;

performing a weight adjustment process on one or more weighting parameters in the application of the PDPC when the block size condition is met, the one or more weighting parameters indicating weights for weighting reference samples, the weights descending along a side of the current block; and

excluding the application of the PDPC in a reconstruction of at least one sample of the current block based on the intra prediction mode when the block size condition is met.

2. The method of claim 1 , wherein the block size condition limits the application of the PDPC in the reconstruction of the current block when the application of the PDPC in the reconstruction of the current block uses additional reference samples other than reference samples used in angular based intra prediction according to the intra prediction mode.

3. The method of claim 1 , further comprising:

determining whether one of a width and a height of the current block is equal to two; and

disabling the application of the PDPC in the reconstruction of the current block when one of the width and the height of the current block is equal to two.

4. The method of claim 1 , further comprising:

determining whether the current block is larger than a size threshold; and

disabling the application of the PDPC in the reconstruction of the current block when the current block is larger than the size threshold.

5. The method of claim 1 , further comprising:

determining whether a ratio of two sides of the current block meets a narrow shape condition; and

disabling the application of the PDPC in the reconstruction of the current block when the ratio meets the narrow shape condition.

6. The method of claim 1 , further comprising:

selecting a subset of samples in the current block for the application of the PDPC;

reconstructing the subset of samples with the application of the PDPC; and

reconstructing at least one other sample in the current block without the application of the PDPC.

7. The method of claim 6 , further comprising:

selecting one or more left columns in the current block for the application of the PDPC when the current block has more columns than rows and the intra prediction mode is a diagonal mode; and

selecting one or more top rows in the current block for the application of the PDPC when the current block has more rows than columns and the intra prediction mode is a diagonal mode.

8. The method of claim 1 , wherein the one or more weighting parameters include a weight for weighting reference samples, and the weight adjustment process comprises:

increasing a descending speed of the weights for weighting the reference samples, the weights descending along the side of the current block according to the descending speed.

9. The method of claim 1 , wherein the weight adjustment process comprises:

reducing an initial value of the weights for weighting the reference samples, the weights descending along the side of the current block from the initial value according to a descending speed of the weights for weighting the reference samples.

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

decoding prediction information of a current block from a coded video bitstream, the prediction information being indicative of an intra prediction mode;

determining whether the current block meets a block size condition that limits an application of a position dependent intra prediction combination (PDPC) in a reconstruction of the current block based on a size of the current block;

performing a weight adjustment process on one or more weighting parameters in the application of the PDPC when the block size condition is met, the one or more weighting parameters including a descending speed for weighting in the PDPC, the weight adjustment process including setting a first descending speed for weighting in the PDPC for a chroma component to be larger than a second descending speed for weighting in the PDPC for a lama component; and

excluding the application of the PDPC in a reconstruction of at least one sample of the current block based on the intra prediction mode when the block size condition is met.

11. The method of claim 1 , further comprising:

disabling the application of the PDPC in a reconstruction of chroma samples.

12. The method of claim 11 , further comprising:

disabling the application of the PDPC in the reconstruction of chroma samples when the intra prediction mode is one in a predefined set of intra prediction modes.

13. The method of claim 1 , further comprising:

determining initial values for the weights that descend along the side of the current block based on at least one of a color index, sizes of the current block and the intra prediction mode.

14. The method of claim 1 , further comprising:

determining whether a reference sample in the application of the PDPC is out of a predefined range; and

setting the weights for the reference sample to be zero when the reference sample is out of the predefined range.

15. An apparatus for video decoding, comprising:

processing circuitry configured to:

decode prediction information of a current block from a coded video bitstream, the prediction information being indicative of an intra prediction mode;

determine whether the current block meets a block size condition that limits an application of a position dependent intra prediction combination (PDPC) in a reconstruction of the current block based on a size of the current block;

perform a weight adjustment process on one or more weighting parameters in the application of the PDPC when the block size condition is met, the one or more weighting parameters indicating weights for weighting reference samples, the weights descending along a side of the current block; and

exclude the application of the PDPC in a reconstruction of at least one sample of the current block based on the intra prediction mode when the block size condition is met.

16. The apparatus of claim 15 , wherein the block size condition limits the application of the PDPC in the reconstruction of the current block when the application of the PDPC in the reconstruction of the current block uses additional reference samples other than reference samples used in angular based intra prediction according to the intra prediction mode.

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

determine whether one of a width and a height of the current block is equal to two; and

disable the application of the PDPC in the reconstruction of the current block when one of the width and the height of the current block is equal to two.

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

determine whether the current block is larger than a size threshold; and

disable the application of the PDPC in the reconstruction of the current block when the current block is larger than the size threshold.

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

determine whether a ratio of two sides of the current block meets a narrow shape condition; and

disable the application of the PDPC in the reconstruction of the current block when the ratio meets the narrow shape condition.

20. The apparatus of claim 15 , wherein when the block size condition is met, the processing circuitry is further configured to:

select a subset of samples in the current block for the application of the PDPC;

reconstruct the subset of samples with the application of the PDPC; and

reconstruct at least one other sample in the current block without the application of the PDPC.