Image decoding method using BDPCM and device therefor
An image decoding method performed by a decoding apparatus according to the present document comprises the steps of: deriving prediction samples for a first sample and a second sample of the current block on the basis of BDPCM-related information about the current block and neighboring samples of the current block; deriving residual samples for the first sample and the second sample on the basis of a residual coefficient of the first sample and a modified residual coefficient of the second sample; and storing, as the intra prediction mode of the current block, the intra prediction mode in the prediction direction of the current block, which is derived on the basis of a BDPCM direction flag.
1. An image decoding method, performed by a decoding apparatus, comprising:
obtaining image information including Block-based Delta Pulse Code Modulation (BDPCM) related information and residual information for a current block;
deriving prediction samples for a first sample and a second sample of the current block based on the BDPCM related information and a neighboring sample of the current block;
deriving residual coefficients of the first sample and the second sample based on the residual information;
deriving a modified residual coefficient of the second sample by adding a residual coefficient of the first sample and a residual coefficient of the second sample;
deriving residual samples for the first sample and the second sample based on the residual coefficient of the first sample and the modified residual coefficient of the second sample;
deriving reconstructed samples for the first sample and the second sample based on the prediction samples and the residual samples; and
storing an intra prediction mode of a prediction direction of the current block derived based on a BDPCM direction flag as an intra prediction mode of the current block,
wherein the BDPCM related information includes the BDPCM direction flag representing the prediction direction,
wherein the first sample is a sample in the current block adjacent to the neighboring sample, and the second sample is a sample in the current block adjacent to the first sample in the prediction direction,
wherein the intra prediction mode stored as the intra prediction mode of the current block is used for prediction for a block coded after the current block, and
wherein the block coded after the current block is a block within a current Coding Tree Unit (CTU) or a neighboring CTU in a current picture or a reference picture.
2. The image decoding method of claim 1 , wherein when a value of the BDPCM direction flag is 0, the BDPCM direction flag represents that the prediction direction for the current block is a horizontal direction, and
wherein when the value of the BDPCM direction flag is 1, the BDPCM direction flag represents that the prediction direction for the current block is a vertical direction.
3. The image decoding method of claim 1 , wherein the prediction direction for the current block is a horizontal direction, the neighboring sample is a left neighboring sample of the current block, the first sample is a sample located in a first column of the current block.
4. The image decoding method of claim 1 , wherein the prediction direction for the current block is a vertical direction, the neighboring sample is a top neighboring sample of the current block, the first sample is a sample located in a first row of the current block.
5. The image decoding method of claim 1 , wherein the BDPCM related information includes a BDPCM flag representing whether BDPCM is applied to the current block.
6. The image decoding method of claim 5 , wherein when a value of the BDPCM flag is 0, the BDPCM direction flag represents that the BDPCM is not applied to the current block,
when the value of the BDPCM flag is 1, the BDPCM direction flag represents that the BDPCM is applied to the current block and the BDPCM direction flag is present.
7. The image decoding method of claim 2 , wherein when the prediction direction is the horizontal direction, a horizontal intra prediction mode is stored as the intra prediction mode of the current block, and
wherein the prediction direction is the vertical direction, a vertical intra prediction mode is stored as the intra prediction mode of the current block.
8. The image decoding method of claim 1 , wherein the stored intra prediction mode is used for prediction of a neighboring block of the current block.
9. An image encoding method, performed by an encoding apparatus, comprising:
deriving prediction samples for a first sample and a second sample of a current block based on Block-based Delta Pulse Code Modulation (BDPCM) and a neighboring sample of the current block;
deriving residual samples for the first sample and the second sample based on the prediction samples;
deriving residual coefficients of the first sample and the second sample based on the residual samples;
encoding residual information of the current block based on the BDPCM and the residual coefficients;
encoding a BDPCM flag representing that the BDPCM is applied to the current block and a BDPCM direction flag representing a prediction direction for the current block; and
storing an intra prediction mode of the prediction direction as an intra prediction mode of the current block,
wherein the first sample is a sample in the current block adjacent to the neighboring sample, and the second sample is a sample in the current block adjacent to the first sample in the prediction direction,
wherein the intra prediction mode stored as the intra prediction mode of the current block is used for prediction for a block coded after the current block, and
wherein the block coded after the current block is a block within a current Coding Tree Unit (CTU) or a neighboring CTU in a current picture or a reference picture.
10. The image encoding method of claim 9 , wherein the residual information includes syntax elements for the first sample representing a residual coefficient for the first sample, and syntax elements for the second sample representing a difference between the residual coefficient for the first sample and a residual coefficient for the second sample.
11. The image encoding method of claim 9 , wherein when a value of the BDPCM direction flag is 0, the BDPCM direction flag represents that the prediction direction for the current block is a horizontal direction,
wherein when the value of the BDPCM direction flag is 1, the BDPCM direction flag represents that the prediction direction for the current block is a vertical direction.
12. The image encoding method of claim 9 , wherein the prediction direction for the current block is a horizontal direction, the neighboring sample is a left neighboring sample of the current block, the first sample is a sample located in a first column of the current block.
13. The image encoding method of claim 9 , wherein the prediction direction for the current block is a vertical direction, the neighboring sample is a top neighboring sample of the current block, the first sample is a sample located in a first row of the current block.
14. The image encoding method of claim 9 , wherein when a value of the BDPCM flag is 0, the BDPCM direction flag represents that the BDPCM is not applied to the current block,
when the value of the BDPCM flag is 1, the BDPCM direction flag represents that the BDPCM is applied to the current block and the BDPCM direction flag is present.
15. A non-transitory computer-readable storage medium storing a bitstream generated by a method, the method comprising:
deriving prediction samples for a first sample and a second sample of a current block based on Block-based Delta Pulse Code Modulation (BDPCM) and a neighboring sample of the current block;
deriving residual samples for the first sample and the second sample based on the prediction samples,
deriving residual coefficients of the first sample and the second sample based on the residual samples,
encoding residual information of the current block based on the BDPCM and the residual coefficients;
encoding a BDPCM flag representing that the BDPCM is applied to the current block and a BDPCM direction flag representing a prediction direction for the current block;
generating the bitstream including the residual information, the BDPCM flag and the BDPCM direction flag; and
storing an intra prediction mode of the prediction direction as an intra prediction mode of the current block,
wherein the first sample is a sample in the current block adjacent to the neighboring sample, and the second sample is a sample in the current block adjacent to the first sample in the prediction direction,
wherein the intra prediction mode stored as the intra prediction mode of the current block is used for prediction for a block coded after the current block, and
wherein the block coded after the current block is a block within a current Coding Tree Unit (CTU) or a neighboring CTU in a current picture or a reference picture.