Method and apparatus of matrix based intra prediction in image and video processing
An intra prediction method includes receiving input data of a current block in a current picture, deriving reference samples of the current block from boundary samples, selecting a matrix for the current block, generating intermediate predicted samples by multiplying the reference samples and the matrix, and clipping the intermediate predicted samples before up-sampling. The intra prediction method further includes performing an up-sampling process on the clipped intermediate predicted samples to generate predicted samples for the current block, and encoding or decoding the current block according to the predicted samples of the current block.
1. A method of image or video coding, comprising:
receiving input data associated with a current block to be processed by matrix-based intra prediction in a current picture, the current block having a size other than 4×4;
deriving reference samples of the current block from neighboring boundary samples of the current block;
selecting a matrix for the current block;
generating intermediate predicted samples by multiplying the reference samples and the matrix;
generating clipped intermediate predicted samples by clipping the intermediate predicted samples to a rational range;
performing an up-sampling process on the clipped intermediate predicted samples to generate final predicted samples for the current block; and
encoding or decoding the current block in the current picture according to the final predicted samples of the current block,
wherein a number of clipping operations performed for producing the final predicted samples for the current block is less than a sample number of the current block.
2. The method of claim 1 , wherein the rational range is [0, 1<<BitDepth−1], and BitDepth is an internal bit depth of the video coding system.
3. The method of claim 1 , wherein the step of deriving reference samples of the current block comprises down-sampling the neighboring boundary samples of the current block to generate the reference samples.
4. The method of claim 1 , wherein the step of deriving reference samples of the current block comprises extracting the reference samples by averaging the neighboring boundary samples of the current block.
5. The method of claim 1 , wherein the step of generating intermediate predicted samples further comprises adding an offset vector after multiplying the reference samples and the matrix.
6. The method of claim 1 , further comprising signaling a matrix index in a video bitstream, wherein the matrix index indicates the matrix selected according to a width and height of the current block.
7. The method of claim 1 , wherein the matrix is selected by parsing a matrix index from a video bitstream and according to a width and height of the current block.
8. The method of claim 1 , wherein the up-sampling process up-samples the clipped intermediate predicted samples to a size of the current block.
9. The method of claim 1 , wherein the up-sampling process performs vertical up-sampling then horizontal up-sampling if a height of the current block is smaller than or equal to a width of the current block, otherwise horizontal up-sampling is performed before vertical up-sampling.
10. The method of claim 1 , wherein the up-sampling process comprises up-sampling by linear interpolation in each direction.
11. The method of claim 1 , further comprising adaptively performing a transposing process to the clipped intermediate predicted samples of the current block before the up-sampling process.
12. An apparatus, comprising a computer processor configured for receiving image or video data and programming executable on the computer processor for performing image or video coding by performing steps comprising:
receiving input data associated with a current block to be processed by matrix-based intra prediction in a current picture, the current block having a size other than 4×4;
deriving reference samples of the current block from neighboring boundary samples of the current block;
selecting a matrix for the current block;
generating intermediate predicted samples by multiplying the reference samples and the matrix;
generating clipped intermediate predicted samples by clipping the intermediate predicted samples to a rational range;
performing an up-sampling process on the clipped intermediate predicted samples to generate final predicted samples for the current block; and
encoding or decoding the current block in the current picture according to the final predicted samples of the current block,
wherein a number of clipping operations performed for producing the final predicted samples for the current block is less than a sample number of the current block.
13. A non-transitory computer readable medium storing program instruction causing a processing circuit of an apparatus to perform a method of image or video coding, and the method comprising:
receiving input data associated with a current block to be processed by matrix-based intra prediction in a current picture, the current block having a size other than 4×4;
deriving reference samples of the current block from neighboring boundary samples of the current block;
selecting a matrix for the current block;
generating intermediate predicted samples by multiplying the reference samples and the matrix;
generating clipped intermediate predicted samples by clipping the intermediate predicted samples to a rational range;
performing an up-sampling process on the clipped intermediate predicted samples to generate final predicted samples for the current block; and
encoding or decoding the current block in the current picture according to the final predicted samples of the current block,
wherein a number of clipping operations performed for producing the final predicted samples for the current block is less than a sample number of the current block.