MPM list-based intra prediction method and device
A video decoding method according to the present document is characterized by comprising: obtaining Most Probable Mode (MPM) index information and reference line index information from a bitstream; compiling an MPM list including candidate intra prediction modes for the intra prediction of a current block; deriving an intra prediction mode for the current block from among the candidate intra prediction modes included in the MPM list on the basis of the MPM index information; generating prediction samples for the current block on the basis of the intra prediction mode; and generating reconstructed samples for the current block on the basis of the prediction samples, wherein the step for compiling the MPM list involves deriving a DC mode as one of the candidate intra prediction modes, and including the DC mode in the MPM list, the DC mode being derived on the basis of the value of reference line index information indicating a reference line used for the intra prediction of the current block not being zero.
1. An image decoding method performed by a decoding apparatus, the method comprising:
obtaining Most Probable Mode (MPM) index information and reference line index information from a bitstream;
constructing a MPM list including candidate intra prediction modes for intra prediction of a current block;
deriving an intra prediction mode for the current block among the candidate intra prediction modes included in the MPM list based on the MPM index information;
generating prediction samples for the current block based on the intra prediction mode; and
generating reconstructed samples for the current block based on the prediction samples,
wherein in the constructing of the MPM list, a DC mode is derived as one of the candidate intra prediction modes and included in the MPM list,
wherein the reference line index information is related to a value indicating a reference line used for intra prediction of the current block, and
wherein based on the value of the reference line index information being not equal to 0, a planar mode is not used as the intra prediction mode of the current block, the planar mode is not included in the MPM list, a number of candidate intra prediction modes in the MPM list is five, and the intra prediction mode of the current block is derived from the MPM list based on the MPM index information.
2. The image decoding method of claim 1 , wherein based on the value of the reference line index information being not equal to 0, planar flag information related to indicating whether the planar mode is used as the intra prediction mode of the current block or not is not signaled, and
wherein a value of the planar flag information is inferred as 1 indicating that the planar mode is not used as the intra prediction mode of the current block.
3. The image decoding method of claim 1 , further comprising constructing a temporary MPM list, wherein, in the constructing of the MPM list, based on a case in which the planar mode is included among candidate intra prediction modes in the temporary MPM list, the MPM list is reconstructed by removing the planar mode.
4. The image decoding method of claim 1 , wherein the DC mode is not used as the intra prediction mode of the current block, based on subpartition mode information related to indicating whether subpartition intra prediction is used for the current block or not.
5. The image decoding method of claim 4 , comprising obtaining the subpartition mode information based on the value of the reference line index information being equal to 0,
wherein based on the subpartition mode information indicating that subpartition intra prediction is used for the current block, the DC mode is not used as the intra prediction mode of the current block.
6. The image decoding method of claim 1 , wherein the reference line index information having a value of 0 means that intra prediction is performed using samples of the first closest reference line to the current block, and
the reference line index information having a non-zero value means that intra prediction is performed using samples of the second, third, or fourth closest reference line to the current block.
7. An image encoding method performed by an encoding apparatus, the method comprising:
generating reference line index information related to a value indicating a reference line used for intra prediction of a current block;
constructing a most probable mode (MPM) list including candidate intra prediction modes for the intra prediction of the current block;
deriving an intra prediction mode for the current block among the candidate intra prediction modes included in the MPM list;
generating MPM index information related to indicating the intra prediction mode for the current block; and
encoding image information including the MPM index information and the reference line index information,
wherein in the constructing of the MPM list, a DC mode is derived as one of the candidate intra prediction modes and included in the MPM list, and
wherein based on the value of the reference line index information being not equal to 0, a planar mode is not used as the intra prediction mode of the current block, the planar mode is not included in the MPM list, a number of candidate intra prediction modes in the MPM list is five, and the MPM index information is generated based on the intra prediction mode of the current block derived from the MPM list.
8. The image encoding method of claim 7 , wherein based on the value of the reference line index information being not equal to 0, planar flag information related to indicating whether the planar mode is used as the intra prediction mode of the current block or not is not signaled, and
wherein a value of the planar flag information is inferred as 1 indicating that the planar mode is not used as the intra prediction mode of the current block.
9. The encoding method of claim 7 , further comprising constructing a temporary MPM list, wherein in the constructing of the MPM list, based on a case in which the planar mode is included among candidate intra prediction modes in the temporary MPM list, the MPM list is reconstructed by removing the planar mode.
10. A non-transitory computer-readable digital storage medium storing a bitstream generated by a method, the method comprising:
generating reference line index information related to a value indicating a reference line used for intra prediction of a current block;
constructing a most probable mode (MPM) list including candidate intra prediction modes for the intra prediction of the current block;
deriving an intra prediction mode for the current block among the candidate intra prediction modes included in the MPM list;
generating MPM index information related to indicating the intra prediction mode for the current block; and
encoding image information including the MPM index information and the reference line index information to generate the bitstream,
wherein in the constructing of the MPM list, a DC mode is derived as one of the candidate intra prediction modes and included in the MPM list, and
wherein based on the value of the reference line index information being not equal to 0, a planar mode is not used as the intra prediction mode of the current block, the planar mode is not included in the MPM list, a number of candidate intra prediction modes in the MPM list is five, and the MPM index information is generated based on the intra prediction mode of the current block derived from the MPM list.