Image decoding method and device thereof

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

obtaining a Block-based Delta Pulse Code Modulation (BDPCM) flag for a current block;

obtaining a BDPCM direction flag for the current block based on the BDPCM flag representing that BDPCM is applied to the current block; and

storing an intra prediction mode of a prediction direction derived based on the BDPCM direction flag as an intra prediction mode of the current block,

wherein the BDPCM direction flag represents a horizontal direction or a vertical direction as the prediction direction,

wherein based on the BDPCM being applied to the current block and the prediction direction for the current block being the vertical direction, residual information includes syntax elements for a target sample of the current block, and

wherein the syntax elements for the target sample represent a difference between a residual coefficient value of the target sample and a top residual coefficient value of the target sample.

2. The image decoding method of claim 1 , further comprising when the prediction direction is the horizontal direction, deriving a prediction sample of the target sample of the current block based on a left neighboring sample of the current block;

deriving a residual coefficient for the target sample based on the residual information;

deriving a modified residual coefficient based on a sum of a left residual coefficient of the residual coefficient and the residual coefficient;

deriving a residual sample for the target sample based on the modified residual coefficient; and

deriving a reconstructed sample for the target sample based on the prediction sample and the residual sample.

3. The image decoding method of claim 1 , further comprising when the prediction direction is the vertical direction, deriving a prediction sample of the target sample of the current block based on a top neighboring sample of the current block;

deriving a residual coefficient for the target sample based on the residual information;

deriving a modified residual coefficient based on a sum of a top residual coefficient of the residual coefficient and the residual coefficient;

deriving a residual sample for the target sample based on the modified residual coefficient; and

deriving a reconstructed sample for the target sample based on the prediction sample and the residual sample.

4. The image decoding method of claim 1 , wherein 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.

5. The image decoding method of claim 1 , wherein when a value of the BDPCM direction flag is 0, the BDPCM direction flag represents the horizontal direction as the prediction direction,

wherein when the value of the BDPCM direction flag is 1, the BDPCM direction flag represents the vertical direction as the prediction direction.

6. The image decoding method of claim 1 , wherein when a 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 1 , wherein the stored intra prediction mode is used for prediction of a neighboring block of the current block.

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

deriving prediction samples of a current block based on Block-based Delta Pulse Code Modulation (BDPCM);

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 BDPCM direction flag represents a horizontal direction or a vertical direction as the prediction direction,

wherein residual samples of the current block are derived based on the prediction sample and residual information for the residual samples is encoded based on the BDPCM,

wherein based on the prediction direction for the current block being the vertical direction, the residual information includes syntax elements for a target residual sample of the current block, and

wherein the syntax elements for the target residual sample represent a difference between a residual coefficient value of the target residual sample and a residual coefficient value of a top neighboring residual sample of the target residual sample.

9. The image encoding method of claim 8 , wherein when a 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.

10. The image encoding method of claim 8 , wherein based on the prediction direction for the current block being the horizontal direction, the residual information includes syntax elements for the target residual sample of the current block, and

wherein the syntax elements for the target residual sample represent a difference between a residual coefficient value of the target residual sample and a residual coefficient value of a left neighboring residual sample of the target residual sample.

11. A non-transitory computer-readable storage medium storing a bitstream generated by a method, the method comprising:

deriving prediction samples of a current block based on Block-based Delta Pulse Code Modulation (BDPCM);

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;

storing an intra prediction mode of the prediction direction as an intra prediction mode of the current block; and

generating the bitstream including the BDPCM flag and the BDPCM direction flag,

wherein the BDPCM direction flag represents a horizontal direction or a vertical direction as the prediction direction,

wherein residual samples of the current block are derived based on the prediction sample and residual information for the residual samples is encoded based on the BDPCM,

wherein based on the prediction direction for the current block being the vertical direction, the residual information includes syntax elements for a target residual sample of the current block, and

wherein the syntax elements for the target residual sample represent a difference between a residual coefficient value of the target residual sample and a residual coefficient value of a top neighboring residual sample of the target residual sample.