Matrix-based intra prediction device and method

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

receiving second flag information related to whether matrix-based intra prediction (MIP) is used for a current block based on first flag information related to whether the MIP is enabled;

receiving MIP mode information based on the second flag information;

generating intra prediction samples for the current block based on the MIP mode information and a size of the current block; and

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

wherein the MIP mode information is index information related to an MIP matrix for the current block,

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

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

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

2. The image decoding method of claim 1 , wherein the first flag information is signaled through sequence parameter set (SPS) syntax information, and

wherein the second flag information is signaled through coding unit syntax information.

3. The image decoding method of claim 2 , 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 the 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. The image decoding method of claim 3 , wherein the reduced boundary samples are downsampled by averaging the reference samples, and

wherein the intra prediction samples are upsampled by linear interpolation of the reduced prediction samples.

7. 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; and

encoding information on the residual samples and information on the MIP,

wherein the information on the MIP comprises first flag information related to whether the MIP is enabled, second flag information related to whether the MIP is applied to the current block and MIP mode information which is index information related to an MIP matrix for the current block,

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

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

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

8. The image encoding method of claim 7 , wherein the first flag information is encoded in sequence parameter set (SPS) syntax information, and

wherein the second flag information is encoded in coding unit syntax information.

9. The image encoding method of claim 8 , 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. The image encoding method of claim 9 , 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.

11. The image encoding method of claim 10 , wherein the index information indicates any one of the plurality of MIP matrices comprised in one matrix set.

12. The image encoding method of claim 9 , wherein the reduced boundary samples are downsampled by averaging the reference samples, and

wherein the intra prediction samples are upsampled by linear interpolation of the reduced prediction samples.

13. 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; and

encoding information on the residual samples and information on the MIP to generate the bitstream,

wherein the information on the MIP comprises first flag information related to whether the MIP is enabled, second flag information related to whether the MIP is applied to the current block and MIP mode information which is index information related to an MIP matrix for the current block,

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

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

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