Context coding for matrix-based intra prediction

An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:

• determine, for a conversion between a current video block of a video and a bitstream of the video, whether a matrix intra prediction (MIP) mode is applied on the current video block based on a syntax element, wherein in the MIP mode, prediction samples of the current video block are determined by performing a matrix vector multiplication operation;
• and
• perform the conversion based on the determining,
• wherein at least one bin of the syntax element is context coded, and an increasement value of the context is determined based on characteristics of a neighboring block of the current video block,
• wherein a boundary down-sampling operation on reference samples of the current video block and an up-sampling operation are included in the MIP mode based on a size of the current video block, and
• wherein in the boundary down-sampling operation, reduced boundary samples are directly generated from the reference samples and a downscaling factor without generating intermediate samples.

A non-transitory computer-readable storage medium storing instructions that cause a processor to:

• determine, for a conversion between a current video block of a video and a bitstream of the video, whether a matrix intra prediction (MIP) mode is applied on the current video block based on a syntax element, wherein in the MIP mode, prediction samples of the current video block are determined by performing a matrix vector multiplication operation;
• and
• perform the conversion based on the determining,
• wherein at least one bin of the syntax element is context coded, and an increasement value of the context is determined based on characteristics of a neighboring block of the current video block,
• wherein a boundary down-sampling operation on reference samples of the current video block and an up-sampling operation are included in the MIP mode based on a size of the current video block, and
• wherein in the boundary down-sampling operation, reduced boundary samples are directly generated from the reference samples and a downscaling factor without generating intermediate samples.

A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises:

• determining whether a matrix intra prediction (MIP) mode is applied on a current video block of the video based on a syntax element, wherein in the MIP mode, prediction samples of the current video block are determined by performing a matrix vector multiplication operation;
• and
• generating the bitstream based on the determining,
• wherein at least one bin of the syntax element is context coded, and an increasement value of the context is determined based on characteristics of a neighboring block of the current video block,
• wherein a boundary down-sampling operation on reference samples of the current video block and an up-sampling operation are included in the MIP mode based on a size of the current video block, and
• wherein in the boundary down-sampling operation, reduced boundary samples are directly generated from the reference samples and a downscaling factor without generating intermediate samples.