Method and apparatus for prediction and transform for small blocks
A method of video decoding for a video decoder includes determining whether a block size of a chroma block is less than or equal to a block size threshold. The method further includes, in response to a determination that the block size of the chroma block is greater than the block size threshold, selecting an intra prediction mode for the chroma block from a plurality of intra prediction modes. The method further includes, in response to a determination that the block size of the chroma block is less than or equal to the block size threshold, selecting the intra prediction mode for the chroma block from a subset of the plurality of intra prediction modes. The method further includes performing intra prediction for the chroma block based on a chroma sample obtained with the selected intra prediction mode.
1. A method of video decoding for a video decoder, the method comprising:
determining whether a block size of a chroma block is less than or equal to a block size threshold;
in response to a determination that the block size of the chroma block is greater than the block size threshold, selecting an intra prediction mode for the chroma block from a plurality of intra prediction modes to obtain a chroma sample;
in response to a determination that the block size of the chroma block is less than or equal to the block size threshold, selecting the intra prediction mode for the chroma block from a subset of the plurality of intra prediction modes that includes one or more prediction modes that are dependent on an intra prediction mode of a luma block associated with the chroma block, the one or more prediction modes including a Cross Correlation Linear Model (CCLM) mode that derives the chroma sample from a luma sample of the luma block associated with the chroma block; and
performing intra prediction for the chroma block based on the chroma sample obtained with the selected intra prediction mode.
2. The method of claim 1 , wherein the one or more prediction modes in the subset of the plurality of intra prediction modes further include a direct copy mode (DM) that reuses the intra prediction mode of the luma block associated with the chroma block.
3. The method of claim 1 , wherein the one or more prediction modes in the subset of the plurality of intra prediction modes consist of the CCLM mode, wherein the luma sample is obtained in accordance with the intra prediction mode of the luma block.
4. The method of claim 1 , wherein only one DC coefficient is signaled for the chroma block having a block size that is less than or equal to the block size threshold.
5. The method of claim 1 , wherein no transform coefficient is signaled for the chroma block having a block size that is less than or equal to the block size threshold.
6. The method of claim 1 , wherein the block size threshold is N×Y, wherein N is an integer greater than 2 and Y is an integer greater than 2, and wherein the block size of the chroma block is less than or equal to the block size threshold in response to a determination that a height of the chroma block is less than or equal to N or a width of the chroma block is less than or equal to Y.
7. The method of claim 1 , wherein the block size threshold is one of a block area, block width, and block height of a smallest luma intra coded block unit size.
8. The method of claim 1 , wherein the block size threshold and the block size of the chroma block is a number of pixels.
9. A video decoder for video decoding, comprising:
processing circuitry configured to:
determine whether a block size of a chroma block is less than or equal to a block size threshold;
in response to a determination that the block size of the chroma block is greater than the block size threshold, select an intra prediction mode for the chroma block from a plurality of intra prediction modes to obtain a chroma sample;
in response to a determination that the block size of the chroma block is less than or equal to the block size threshold, select the intra prediction mode for the chroma block from a subset of the plurality of intra prediction modes that includes one or more prediction modes that are dependent on an intra prediction mode of a luma block associated with the chroma block, the one or more prediction modes including a Cross Correlation Linear Model (CCLM) mode that derives the chroma sample from a luma sample of the luma block associated with the chroma block; and
perform intra prediction for the chroma block based on the chroma sample obtained with the selected intra prediction mode.
10. The video decoder of claim 9 , wherein the one or more prediction modes in the subset of the plurality of intra prediction modes further includes a direct copy mode (DM) that reuses the intra prediction mode of the luma block associated with the chroma block.
11. The video decoder of claim 9 , wherein the one or more prediction modes in the subset of the plurality of intra prediction modes consist of the CCLM mode, wherein the luma sample is obtained in accordance with the intra prediction mode of the luma block.
12. The video decoder of claim 9 , wherein only one DC coefficient is signaled for the chroma block having a block size that is less than or equal to the block size threshold.
13. The video decoder of claim 9 , wherein no transform coefficient is signaled for the chroma block having a block size that is less than or equal to the block size threshold.
14. A non-transitory computer readable medium having instructions stored therein, which when executed by a processor in a video decoder causes the processor to execute a method comprising:
determining whether a block size of a chroma block is less than or equal to a block size threshold;
in response to a determination that the block size of the chroma block is greater than the block size threshold, selecting an intra prediction mode for the chroma block from a plurality of intra prediction modes to obtain a chroma sample;
in response to a determination that the block size of the chroma block is less than or equal to the block size threshold, selecting the intra prediction mode for the chroma block from a subset of the plurality of intra prediction modes that includes one or more prediction modes that are dependent on an intra prediction mode of a luma block associated with the chroma block, the one or more prediction modes including a Cross Correlation Linear Model (CCLM) mode that derives the chroma sample from a luma sample of the luma block associated with the chroma block; and
performing intra prediction for the chroma block based on the chroma sample obtained with the selected intra prediction mode.