Matrix-based intra prediction device and method

1. An image decoding method performed by a decoding apparatus, the method comprising:

obtaining image information including residual information and flag information related to whether matrix-based intra prediction (MIP) is used for a current block, from a bitstream;

obtaining matrix-based intra prediction (MIP) mode information based on the flag information;

generating intra prediction samples for the current block based on the MIP mode information;

generating residual samples for the current block based on the residual information; and

generating reconstructed samples for the current block based on the intra prediction samples and the residual samples,

wherein a syntax element bin string for the MIP mode information is binarized by a truncated binary (TB) binarization method,

wherein a maximum length of the syntax element bin string is set to different three values based on a size of the current block,

wherein the maximum length has a largest value based on a width and a height of the current block being 4,

wherein an MIP matrix is derived based on the MIP mode information, and

wherein the intra prediction samples are generated based on the MIP matrix,

wherein the MIP mode information is index information related to the MIP matrix applied to the current block.

2. The image decoding method of claim 1 , wherein the MIP mode information is decoded in a bypass method.

3. The image decoding method of claim 1 , wherein the generating of the intra prediction samples comprises:

deriving reduced boundary samples by downsampling reference samples adjacent to the current block;

deriving reduced prediction samples based on a multiplication operation of the reduced boundary samples and an MIP matrix; and

generating the intra prediction samples for the current block by upsampling the reduced prediction samples.

4. The image decoding method of claim 3 , wherein the MIP matrix is derived based on the size of the current block and the index information.

5. The image decoding method of claim 4 , wherein the MIP matrix is selectable from any one of three matrix sets classified according to the size of the current block, and

wherein each of the three matrix sets comprises a plurality of MIP matrices.

6. An image encoding method performed by an encoding apparatus, the method comprising:

deriving whether matrix-based intra prediction (MIP) is applied to a current block;

deriving intra prediction samples for the current block based on the MIP when the MIP is applied to the current block;

deriving residual samples for the current block based on the intra prediction samples;

generating residual information based on the residual samples; and

encoding image information including the residual information and matrix-based intra prediction (MIP) mode information,

wherein a syntax element bin string for the MIP mode information is binarized by a truncated binary (TB) binarization method,

wherein a maximum length of the syntax element bin string is set to different three values based on a size of the current block,

wherein the maximum length has a largest value based on a width and a height of the current block being 4,

wherein an MIP matrix is derived based on the MIP mode information, and

wherein the intra prediction samples are generated based on the MIP matrix,

wherein the MIP mode information is index information related to the MIP matrix applied to the current block.

7. The image encoding method of claim 6 , wherein the MIP mode information is encoded in a bypass method.

8. The image encoding method of claim 6 , wherein the MIP matrix is selected from any one of three matrix sets classified according to the size of the current block,

wherein each of the three matrix sets includes a plurality of MIP matrices, and

wherein the MIP mode information is index information related to any one of the plurality of MIP matrices included in one matrix set.

9. The image encoding method of claim 6 , wherein the generating of the intra prediction samples comprises:

deriving reduced boundary samples by downsampling reference samples adjacent to the current block;

deriving reduced prediction samples based on a multiplication operation of the reduced boundary samples and an MIP matrix; and

generating the intra prediction samples for the current block by upsampling the reduced prediction samples.

10. A non-transitory computer-readable digital storage medium that stores a bitstream generated by a method, the method comprising:

deriving whether matrix-based intra prediction (MIP) is applied to a current block;

deriving intra prediction samples for the current block based on the MIP when the MIP is applied to the current block;

deriving residual samples for the current block based on the intra prediction samples;

generating residual information based on the residual samples; and

encoding image information including the residual information and matrix-based intra prediction (MIP) mode information to generate the bitstream,

wherein a syntax element bin string for the MIP mode information is binarized by a truncated binary (TB) binarization method,

wherein a maximum length of the syntax element bin string is set to different three values based on a size of the current block,

wherein the maximum length has a largest value based on a width and a height of the current block being 4,

wherein an MIP matrix is derived based on the MIP mode information, and

wherein the intra prediction samples are generated based on the MIP matrix,

wherein the MIP mode information is index information related to the MIP matrix applied to the current block.