Methods and devices for intra sub-partition coding mode

A computing device comprising:

• one or more processors;
• a non-transitory computer-readable memory storing instructions executable by the one or more processors, wherein the one or more processors are configured to:
• partition a block of video data into a plurality of sub-partitions, wherein each sub-partition comprises N×M samples where N and M are number of samples in horizontal or vertical direction;
• obtain a number of most probable intra predictions based on intra prediction modes of neighboring blocks of a current block and determining an intra prediction mode to predict the samples of the block sub-partitions;
• select an optimal transform combination from discrete cosine transform II (DCT-II), discrete sine transform VII (DST-VII), and discrete cosine transform VIII (DCT-VIII) transform kernels for each sub-partition, wherein selecting the optimal transform combination comprises applying a multiple transform selection (MTS) mode to an intra sub-partition (ISP) mode the ISP, wherein the optimal transform combination is indicated by one MTS flag and one MTS index;
• obtain residual coefficients of a first sub-partition and deriving dequantized residual coefficients of the first sub-partition by performing inverse-quantization of the residual coefficients of the first sub-partition;
• derive residual samples of the first sub-partition by performing inverse transforms on dequantized residual coefficients of the first sub-partition in horizontal and vertical directions, wherein the inverse transforms are based on the optimal transform combination of the first sub-partition;
• derive prediction samples of the first sub-partition by performing intra prediction of the first sub-partition based on reconstructed samples adjacent to the first sub-partition;
• derive the reconstructed samples of the first sub-partition by adding the residual samples of the first sub-partition to the prediction samples of the first sub-partition;
• and
• derive prediction samples of a second sub-partition by performing intra prediction of the second sub-partition based on the reconstructed samples of the first sub-partition,
• wherein the one or more processors are further configured to:
• select horizontal and vertical transforms by receiving one MTS flag for the block and one MTS index for each sub-partition, wherein the MTS flag is shared by sub-partitions.

A non-transitory computer-readable storage medium storing a plurality of programs for execution by a computing device having one or more processors, wherein the plurality of programs, when executed by the one or more processors, cause the computing device to perform:

• partitioning a block of video data into a plurality of sub-partitions, wherein each sub-partition comprises N×M samples where N and M are number of samples in horizontal or vertical direction;
• obtaining a number of most probable intra predictions based on intra prediction modes of neighboring blocks of a current block and determining an intra prediction mode to predict the samples of the block sub-partitions;
• selecting an optimal transform combination from discrete cosine transform II (DCT-II), discrete sine transform VII (DST-VII), and discrete cosine transform VIII (DCT-VIII) transform kernels for each sub-partition, wherein selecting the optimal transform combination comprises applying a multiple transform selection (MTS) mode to an intra sub-partition (ISP) mode the ISP, wherein the optimal transform combination is indicated by one MTS flag and one MTS index;
• obtaining residual coefficients of a first sub-partition and deriving dequantized residual coefficients of the first sub-partition by performing inverse-quantization of the residual coefficients of the first sub-partition;
• deriving residual samples of the first sub-partition by performing inverse transforms on dequantized residual coefficients of the first sub-partition in horizontal and vertical directions, wherein the inverse transforms are based on the optimal transform combination of the first sub-partition;
• deriving prediction samples of the first sub-partition by performing intra prediction of the first sub-partition based on reconstructed samples adjacent to the first sub-partition;
• deriving the reconstructed samples of the first sub-partition by adding the residual samples of the first sub-partition to the prediction samples of the first sub-partition;
• and
• deriving prediction samples of a second sub-partition by performing intra prediction of the second sub-partition based on the reconstructed samples of the first sub-partition,
• wherein the plurality of programs caused the computing device to perform applying the MTS mode to the ISP further cause the computing device to perform:
• selecting horizontal and vertical transforms by receiving one MTS flag for the block and one MTS index for each sub-partition, wherein the MTS flag is shared by sub-partitions.