Inter prediction-based image coding method and device
An image decoding method according to the present document may comprise: a step for deriving an inter prediction mode from encoded information; a step for constructing reference pictures lists; a step for deriving motion information including reference picture indices for symmetric motion vector differences (SMVD) on the basis of reference pictures included in the reference picture lists; and a step for generating prediction samples on the basis of the motion information. The reference picture indices for SMVD may be derived on the basis of short-term reference pictures included in the reference picture lists.
1 . An image decoding method performed by a decoding apparatus, the method comprising:
obtaining image information including prediction related information from a bitstream;
deriving an inter prediction mode for a current block based on the prediction related information;
deriving reference picture lists for the current block;
deriving picture order count (POC) differences between each of reference pictures included in the reference picture lists and a current picture including the current block;
deriving reference picture indices for symmetric motion vector differences (SMVD) based on the POC differences;
deriving motion vectors for the current block using motion vector predictors (MVPs) for the current block indicated by MVP indices, wherein information on the MVP indices is included in the prediction related information, and
generating prediction samples for the current block based on motion information including the reference picture indices and the motion vectors,
wherein the reference picture indices for the SMVD are derived based on short-term reference pictures among the reference pictures included in the reference picture lists, and
wherein the reference picture indices for the SMVD are not derived based on a long-term reference picture among the reference pictures included in the reference picture lists.
2 . An image encoding method performed by an encoding apparatus, the method comprising:
deriving an inter prediction mode for a current block;
deriving reference picture lists including reference pictures for the current block;
deriving picture order count (POC) differences between the reference pictures included in the reference picture lists and a current picture including the current block;
deriving reference picture indices for symmetric motion vector differences (SMVD) based on the POC differences;
deriving motion vectors for the current block using the inter prediction mode;
generating prediction samples for the current block based on motion information including the reference picture indices and the motion vectors;
generating prediction related information including information on the inter prediction mode;
deriving residual information based on the prediction samples; and
encoding image information including the prediction related information and the residual information,
wherein the reference picture indices for SMVD are based on short-term reference pictures among the reference pictures included in the reference picture lists, and
wherein the reference picture indices for the SMVD are not derived based on a long-term reference picture among the reference pictures included in the reference picture lists.
3 . A non-transitory computer readable storage medium storing a bitstream and computer instruction, which when executed by a processor, causes the processor to perform the image encoding method of claim 2 to generate the bitstream.
4 . A transmission method of data for an image, the method comprising:
obtaining a bitstream for the image, wherein the bitstream is generated based on deriving an inter prediction mode for a current block, deriving reference picture lists including reference pictures, deriving picture order count (POC) differences between the reference pictures included in the reference picture lists and the current picture, deriving motion information including reference picture indices for symmetric motion vector differences (SMVD) based on the POC differences, generating predicted samples based on the motion information, generating prediction related information including the inter prediction mode, deriving residual information based on the predicted samples, and encoding image information including the prediction related information and the residual information; and
transmitting the data comprising the bitstream,
wherein the reference picture indices for SMVD are based on short-term reference pictures among the reference pictures included in the reference picture lists, and
wherein the reference picture indices for the SMVD are not derived based on a long-term reference picture among the reference pictures included in the reference picture lists.