Dmvr-based inter-prediction method and device

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

• determining luma weight L0 flag information related to indicating whether a weight factor for L0 prediction is present and luma weight L1 flag information related to indicating whether a weight factor for L1 prediction is present;
• determining to apply decoder-side motion vector refinement (DMVR) to an L0 motion vector and an L1 motion vector of a current block, based on a case where a value of the luma weight L0 flag information and a value of the luma weight L1 flag information are both equal to 0;
• deriving a refined L0 motion vector and a refined L1 motion vector by applying the DMVR to the current block;
• deriving prediction samples for the current block based on the L0 prediction using the refined L0 motion vector and the L1 prediction using the refined L1 motion vector;
• deriving residual samples based on the prediction samples;
• and
• encoding image information including information on the residual samples,
• wherein in the deriving of the prediction samples for the current block, based on the case where the value of the luma weight L0 flag information and the value of the luma weight L1 flag information are both equal to 0, the prediction samples are derived by applying bi-directional optical flow (BDOF) to the current block.

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

• determining luma weight L0 flag information related to indicating whether a weight factor for L0 prediction is present and luma weight L1 flag information related to indicating whether a weight factor for L1 prediction is present;
• determining to apply decoder-side motion vector refinement (DMVR) to an L0 motion vector and an L1 motion vector of a current block, based on a case where a value of the luma weight L0 flag information and a value of the luma weight L1 flag information are both equal to 0;
• deriving a refined L0 motion vector and a refined L1 motion vector by applying the DMVR to the current block;
• deriving prediction samples for the current block based on the L0 prediction using the refined L0 motion vector and the L1 prediction using the refined L1 motion vector;
• deriving residual samples based on the prediction samples;
• and
• encoding image information including information on the residual samples to generate the bitstream,
• wherein in the deriving of the prediction samples for the current block, based on the case where the value of the luma weight L0 flag information and the value of the luma weight L1 flag information are both equal to 0, the prediction samples are derived by applying bi-directional optical flow (BDOF) to the current block.