Dmvr and bdof based inter prediction method and apparatus thereof

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

• deriving an L0 motion vector and an L1 motion vector for a current block;
• deriving a refined L0 motion vector and a refined L1 motion vector based on the L0 motion vector and the L1 motion vector, by applying Decoder-side Motion Vector Refinement (DMVR) to the current block based on DMVR flag information for representing whether to apply the DMVR to the current block;
• deriving L0 prediction samples of the current block based on the refined L0 motion vector and L1 prediction samples of the current block based on the refined L1 motion vector;
• deriving prediction samples for the current block based on the L0 prediction samples and the L1 prediction samples, by applying Bi-directional optical flow (BDOF) to the current block based on BDOF flag information for representing whether to apply the BDOF to the current block;
• and
• generating reconstruction samples for the current block based on the prediction samples,
• wherein the DMVR flag information is derived based on bi-prediction weight index information, L0 luma weight prediction flag information, L1 luma weight prediction flag information, L0 chroma weight prediction flag information and L1 chroma weight prediction flag information,
• wherein based on the bi-prediction weight index information being equal to 0, both the L0 luma weight prediction flag information and the L1 luma weight prediction flag information being equal to 0, and both the L0 chroma weight prediction flag information and the L1 chroma weight prediction flag information being equal to 0, the DMVR flag information is derived as a value related to applying the DMVR to the current block,
• wherein the BDOF flag information is derived based on the bi-prediction weight index information, the L0 luma weight prediction flag information, the L1 luma weight prediction flag information, the L0 chroma weight prediction flag information and the L1 chroma weight prediction flag information,
• wherein based on the bi-prediction weight index information being equal to 0, both the L0 luma weight prediction flag information and the L1 luma weight prediction flag information being equal to 0, and both the L0 chroma weight prediction flag information and the L1 chroma weight prediction flag information being equal to 0, the BDOF flag information is derived as a value related to applying the BDOF to the current block.

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

• deriving an L0 motion vector and an L1 motion vector for a current block;
• deriving a refined L0 motion vector and a refined L1 motion vector based on the L0 motion vector and the L1 motion vector, by applying Decoder-side Motion Vector Refinement (DMVR) to the current block based on DMVR flag information for representing whether to apply the DMVR to the current block;
• deriving L0 prediction samples of the current block based on the refined L0 motion vector and L1 prediction samples of the current block based on the refined L1 motion vector;
• deriving prediction samples for the current block based on the L0 prediction samples and the L1 prediction samples, by applying Bi-directional optical flow (BDOF) to the current block based on BDOF flag information for representing whether to apply the BDOF to the current block;
• deriving residual samples based on the prediction samples;
• and
• encoding image information including information on the residual samples,
• wherein the DMVR flag information is derived based on bi-prediction weight index information, L0 luma weight prediction flag information, L1 luma weight prediction flag information, L0 chroma weight prediction flag information and L1 chroma weight prediction flag information,
• wherein based on the bi-prediction weight index information being equal to 0, both the L0 luma weight prediction flag information and the L1 luma weight prediction flag information being equal to 0, and both the L0 chroma weight prediction flag information and the L1 chroma weight prediction flag information being equal to 0, the DMVR flag information is derived as a value related to applying the DMVR to the current block,
• wherein the BDOF flag information is derived based on the bi-prediction weight index information, the L0 luma weight prediction flag information, the L1 luma weight prediction flag information, the L0 chroma weight prediction flag information and the L1 chroma weight prediction flag information,
• wherein based on the bi-prediction weight index information being equal to 0, both the L0 luma weight prediction flag information and the L1 luma weight prediction flag information being equal to 0, and both the L0 chroma weight prediction flag information and the L1 chroma weight prediction flag information being equal to 0, the BDOF flag information is derived as a value related to applying the BDOF to the current block.

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

• deriving an L0 motion vector and an L1 motion vector for a current block;
• deriving a refined L0 motion vector and a refined L1 motion vector based on the L0 motion vector and the L1 motion vector, by applying Decoder-side Motion Vector Refinement (DMVR) to the current block based on DMVR flag information for representing whether to apply the DMVR to the current block;
• deriving L0 prediction samples of the current block based on the refined L0 motion vector and L1 prediction samples of the current block based on the refined L1 motion vector;
• deriving prediction samples for the current block based on the L0 prediction samples and the L1 prediction samples, by applying Bi-directional optical flow (BDOF) to the current block based on BDOF flag information for representing whether to apply the BDOF to the current block;
• deriving residual samples based on the prediction samples;
• and
• encoding image information including information on the residual samples to generate the bitstream,
• wherein the DMVR flag information is derived based on bi-prediction weight index information, L0 luma weight prediction flag information, L1 luma weight prediction flag information, L0 chroma weight prediction flag information and L1 chroma weight prediction flag information,
• wherein based on the bi-prediction weight index information being equal to 0, both the L0 luma weight prediction flag information and the L1 luma weight prediction flag information being equal to 0, and both the L0 chroma weight prediction flag information and the L1 chroma weight prediction flag information being equal to 0, the DMVR flag information is derived as a value related to applying the DMVR to the current block,
• wherein the BDOF flag information is derived based on the bi-prediction weight index information, the L0 luma weight prediction flag information, the L1 luma weight prediction flag information, the L0 chroma weight prediction flag information and the L1 chroma weight prediction flag information,
• wherein based on the bi-prediction weight index information being equal to 0, both the L0 luma weight prediction flag information and the L1 luma weight prediction flag information being equal to 0, and both the L0 chroma weight prediction flag information and the L1 chroma weight prediction flag information being equal to 0, the BDOF flag information is derived as a value related to applying the BDOF to the current block.