Motion vector prediction-based image/video coding method and device
An image decoding method according to the present document comprises: decoding a current block on the basis of image information, wherein an MVP candidate list for the current block is derived on the basis of an inter prediction mode, which is derived on the basis of image information, and peripheral blocks of the current block; and deriving motion information of the current block on the basis of the MVP candidate list, wherein the peripheral blocks include a left bottom corner peripheral block, a left peripheral block, a right top corner peripheral block, a top peripheral block, and a left top corner peripheral block of the current block, the motion information includes an L0 motion vector for L0 prediction and/or an L1 motion vector for L1 prediction, the L0 motion vector is derived on the basis of an L0 motion vector predictor and an L0 motion vector difference, and the L1 motion vector is derived on the basis of an L1 motion vector predictor and an L1 motion vector difference.
1. An image decoding method performed by a decoding apparatus, the method comprising:
obtaining image information from a bitstream;
deriving inter prediction mode for a current block based on the image information;
deriving a motion vector predictor (MVP) candidate list for the current block based on the inter prediction mode and neighboring blocks of the current block;
deriving motion information of the current block based on the MVP candidate list;
generating prediction samples of the current block based on the motion information;
generating reconstructed samples based on the prediction samples,
wherein the neighboring blocks include a bottom-left corner neighboring block, a left neighboring block, a top-right corner neighboring block, a top neighboring block and a top-left corner neighboring block,
wherein the motion information includes at least one of an L0 motion vector for L0 prediction or an L1 motion vector for L1 prediction,
wherein the L0 motion vector is derived based on an L0 motion vector predictor and an L0 motion vector difference, and the L1 motion vector is derived based on an L1 motion vector predictor and an L1 motion vector difference,
wherein the image information includes an L1 motion vector difference zero flag, and
wherein the image information includes a coding unit (CU) syntax for the current block,
wherein based on a value of a symmetric motion vector difference reference index for the current block, the CU syntax includes a symmetric motion vector differences (SMVD) flag for the current block,
wherein based on a case where a value of the SMVD flag is 1, the L1 motion vector difference is derived from the L0 motion vector difference, and
wherein based on a case where a value of the L1 motion vector difference zero flag is 1, the L1 motion vector difference is derived as 0 only when the value of the SMVD flag is not 1.
2. The image decoding method of claim 1 , wherein the image information includes header information, and
wherein the header information includes the L1 motion vector difference zero flag.
3. The image decoding method of claim 1 , wherein the image information includes sequence parameter set (SPS),
wherein the SPS include SMVD enabled flag,
wherein the CU syntax includes inter prediction type information and an inter affine flag,
wherein the inter prediction type information indicate whether bi-prediction is applied to the current block,
wherein the CU syntax include the SMVD flag further based on the SMVD enabled flag, the inter prediction type information and the inter affine flag.
4. The image decoding method of claim 1 , wherein an absolute value of the L1 motion vector difference is equal to an absolute value of the L0 motion vector difference, and wherein a sign of the L1 motion vector difference is different from a sign of the L0 motion vector difference.
5. An image encoding method performed by an encoding apparatus, the method comprising:
deriving a motion vector predictor (MVP) candidate list for a current block based on inter prediction mode and neighboring blocks of the current block;
generating information for indicating motion information of the current block based on the MVP candidate list; and
encoding image information including at least one of information on the inter prediction mode or the information for indicating the motion information of the current block,
wherein the neighboring blocks include a bottom-left corner neighboring block, a left neighboring block, a top-right corner neighboring block, a top neighboring block and a top-left corner neighboring block,
wherein the motion information includes at least one of an L0 motion vector for L0 prediction or an L1 motion vector for L1 prediction,
wherein the L0 motion vector is derived based on an L0 motion vector predictor and an L0 motion vector difference, and the L1 motion vector is derived based on an L1 motion vector predictor and an L1 motion vector difference,
wherein the image information includes an L1 motion vector difference zero flag, and
wherein the image information includes a coding unit (CU) syntax for the current block,
wherein based on a value of a symmetric motion vector difference reference index for the current block, the CU syntax includes a symmetric motion vector differences (SMVD) flag for the current block,
wherein based on a case where a value of the SMVD flag is 1, the L1 motion vector difference is derived from the L0 motion vector difference, and
wherein based on a case where a value of the L1 motion vector difference zero flag is 1, the L1 motion vector difference is derived as 0 only when the value of the SMVD flag is not 1.
6. The image encoding method of claim 5 , wherein the image information includes header information, and
wherein the header information includes the L1 motion vector difference zero flag.
7. The image encoding method of claim 5 , wherein the image information includes sequence parameter set (SPS),
wherein the SPS include SMVD enabled flag,
wherein the CU syntax includes inter prediction type information and an inter affine flag,
wherein the inter prediction type information indicate whether bi-prediction is applied to the current block,
wherein the CU syntax include the SMVD flag further based on the SMVD enabled flag, the inter prediction type information and the inter affine flag.
8. The image decoding method of claim 5 , wherein an absolute value of the L1 motion vector difference is equal to an absolute value of the L0 motion vector difference, and
wherein a sign of the L1 motion vector difference is different from a sign of the L0 motion vector difference.
9. An apparatus for transmitting data for image information, comprising:
at least one processor configured to obtain a bitstream for the image information, wherein the bitstream is generated based on deriving a motion vector predictor (MVP) candidate list for a current block based on inter prediction mode and neighboring blocks of the current block,
generating information for indicating motion information of the current block based on the MVP candidate list, and
encoding image information to generate the bitstream, wherein the image information includes at least one of information on the inter prediction mode or the information for indicating the motion information of the current block; and
a transmitter configured to transmit the data including the bitstream,
wherein the neighboring blocks includes a bottom-left corner neighboring block, a left neighboring block, a top-right corner neighboring block, a top neighboring block and a top-left corner neighboring block,
wherein the motion information includes at least one of an L0 motion vector for L0 prediction or an L1 motion vector for L1 prediction,
wherein the L0 motion vector is derived based on an L0 motion vector predictor and an L0 motion vector difference, and the L1 motion vector is derived based on an L1 motion vector predictor and an L1 motion vector difference,
wherein the image information includes an L1 motion vector difference zero flag, and
wherein the image information includes a coding unit (CU) syntax for the current block,
wherein based on a value of a symmetric motion vector difference reference index for the current block, the CU syntax includes a symmetric motion vector differences (SMVD) flag for the current block,
wherein based on a case where a value of the SMVD flag is 1, the L1 motion vector difference is derived from the L0 motion vector difference, and
wherein based on a case where a value of the L1 motion vector difference zero flag is 1, the L1 motion vector difference is derived as 0 only when the value of the SMVD flag is not 1.