DMVR-based inter-prediction method and device

An encoding apparatus for image encoding, the encoding apparatus comprising:

• a memory;
• and
• at least one processor connected to the memory, the at least one processor configured to:
• determine whether an application condition of a decoder-side motion vector refinement (DMVR) for applying a motion vector refinement to a current block is satisfied;
• derive a minimum sum of absolute differences (SAD) based on an L0 motion vector and an L1 motion vector of the current block based on a case where the application condition of the DMVR is satisfied;
• derive a refined L0 motion vector and a refined L1 motion vector for the current block based on the minimum SAD;
• derive prediction samples for the current block based on the refined L0 motion vector and the refined L1 motion vector;
• derive residual samples based on the prediction samples;
• and
• encode image information including information on the residual samples,
• wherein whether the application condition of the DMVR is satisfied is determined based on whether a combined inter and intra prediction (CIIP) mode in which an inter prediction and an intra prediction are combined is applied to the current block, wherein the DMVR is applied to the current block based on a case in which the CIIP mode is not applied to the current block,
• wherein the prediction samples are derived based on determining whether an application condition of a bi-directional optical flow (BDOF) for applying a refinement to the prediction samples is satisfied, and
• wherein whether the application condition of the BDOF is satisfied is determined based on whether the CIIP mode is applied to the current block, wherein the BDOF is applied to the prediction samples based on a case in which the CIIP mode is not applied to the current block.

An apparatus for transmitting data for an image, the apparatus comprising:

• at least one processor configured to obtain a bitstream for the image, wherein the bitstream is generated based on determining whether an application condition of a decoder-side motion vector refinement (DMVR) for applying a motion vector refinement to a current block is satisfied, deriving a minimum sum of absolute differences (SAD) based on an L0 motion vector and an L1 motion vector of the current block based on a case where the application condition of the DMVR is satisfied, deriving a refined L0 motion vector and a refined L1 motion vector for the current block based on the minimum SAD, deriving prediction samples for the current block based on the refined L0 motion vector and 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;
• a transmitter configured to transmit the data comprising the bitstream,
• wherein whether the application condition of the DMVR is satisfied is determined based on whether a combined inter and intra prediction (CIIP) mode in which an inter prediction and an intra prediction are combined is applied to the current block, wherein the DMVR is applied to the current block based on a case in which the CIIP mode is not applied to the current block,
• wherein the prediction samples are derived based on determining whether an application condition of a bi-directional optical flow (BDOF) for applying a refinement to the prediction samples is satisfied, and
• wherein whether the application condition of the BDOF is satisfied is determined based on whether the CIIP mode is applied to the current block, wherein the BDOF is applied to the prediction samples based on a case in which the CIIP mode is not applied to the current block.