Image coding method and apparatus using motion vector differences
According to embodiments of the present document, a prediction procedure can be performed for image video coding, and the prediction procedure can comprise merge mode motion vector differences (MMVD) and symmetric motion vector differences (SMVD) according inter prediction. The inter prediction can be performed on the basis of reference pictures of a current picture, and types of the reference pictures (e.g. a long-term reference picture, a short-term reference picture, etc.) can be considered for the inter prediction. Accordingly, performance and coding efficiency in the prediction procedure can be increased.
1. An image decoding method performed by a decoding apparatus, the method comprising:
receiving image information including prediction related information and information on motion vector differences (MVDs) through a bitstream;
deriving an inter prediction mode for a current block based on the prediction related information;
constructing motion vector predictor (MVP) candidate lists for the current block based on neighboring blocks of the current block;
deriving MVPs for the current block based on the MVP candidate lists;
deriving motion information for the current block based on the information on the MVDs and the MVPs; and
generating predicted samples for the current block based on the motion information,
wherein bi-prediction is applied to the current block,
wherein the motion information includes motion vectors (MVs) and symmetric motion vector difference reference indices,
wherein the MVs include an MVL0 for L0 prediction and an MVL1 for L1 prediction,
wherein the symmetric motion vector difference reference indices include a symmetric motion vector difference reference index L0 for the L0 prediction and a symmetric motion vector difference reference index L1 for the L1 prediction,
wherein the information on the MVDs includes information on an MVDL0 for the L0 prediction,
wherein information on an MVDL1 for the L1 prediction is derived based on the information on the MVDL0,
wherein the MVDL0 is derived based on the information on the MVDL0,
wherein the MVDL1 is derived based on the information on the MVDL1,
wherein the symmetric motion vector difference reference index L0 and the symmetric motion vector difference reference index L1 are derived based on short-term reference pictures among reference pictures included in reference picture lists.
2. The method of claim 1 , wherein the MVPs include the MVPL0 for L0 prediction and the MVPL1 for L1 prediction,
the MVL0 is derived based on a sum of the MVDL0 and the MVPL0, and
the MVL1 is derived based on a sum of the MVDL1 and the MVPL1.
3. The method of claim 1 , wherein the prediction related information includes information on symmetric motion vector differences, and
when the value of the information on symmetric motion vector differences is 1, the symmetric motion vector difference reference index L0 and the symmetric motion vector difference reference index L1 are derived based on picture order count (POC) differences between the short-term reference pictures and a current picture including the current block.
4. The method of claim 1 , wherein the size of the MVDL1 is the same as that of the MVDL0, and
the sign of the MVDL1 is opposite to that of the MVDL0.
5. The method of claim 1 , wherein the short-term reference pictures include short-term reference picture L0 and short-term reference picture L1,
the symmetric motion vector difference reference index L0 indicates the short-term reference picture L0, and
the symmetric motion vector difference reference index L1 indicates the short-term reference picture L1.
6. The method of claim 5 , wherein the reference picture lists include reference picture list 0,
the reference picture list 0 includes the short-term reference picture L0, and
the symmetric motion vector difference reference index L0 is derived based on picture order count (POC) differences between each of short-term reference pictures included in the reference picture list 0 and the current picture including the current block.
7. The method of claim 6 , wherein the symmetric motion vector difference reference index L0 is derived based on comparison between the POC differences.
8. The method of claim 7 , wherein the reference picture list 0 further includes another short-term reference picture L0,
the POC differences include a first POC difference between the short-term reference picture L0 and the current picture and a second POC difference between another short-term reference picture L0 and the current picture, and
the first POC difference is smaller than the second POC difference.
9. The method of claim 5 , wherein the prediction related information includes information on symmetric motion vector differences, and
the symmetric motion vector difference reference index L0 and the symmetric motion vector difference reference index L1 are not signaled directly but are derived based on information on the symmetric motion vector differences.
10. An image encoding method performed by an encoding apparatus, the method comprising:
deriving an inter prediction mode for a current block;
constructing motion vector predictor (MVP) candidate lists for the current block based on neighboring blocks of the current block;
deriving MVPs for the current block based on the MVP candidate lists;
generating prediction related information including information on the inter prediction mode and motion vector differences (MVDs) for the current block;
deriving motion information for the current block based on the information on the MVPs and the MVDs;
generating predicted samples for the current block based on the motion information;
generating residual information based on the predicted samples; and
encoding image information including the prediction related information and the residual information,
wherein the motion information includes motion vectors (MVs) and symmetric motion vector difference reference indices,
wherein the MVs include MVL0 for L0 prediction and MVL1 for L1 prediction,
wherein the symmetric motion vector difference reference indices include the symmetric motion vector difference reference index L0 for L0 prediction and the symmetric motion vector difference reference index L1 for L1 prediction,
wherein the information on the MVDs includes the information on the MVDL0 for L0 prediction,
wherein the information on the MVDL1 for L1 prediction is derived based on the information on the MVDL0,
wherein the MVL0 is derived based on the information on the MVDL0,
wherein the MVL1 is derived based on the information on the MVDL1,
wherein the symmetric motion vector difference reference index L0 and the symmetric motion vector difference reference index L1 are derived based on short-term reference pictures among reference pictures included in reference picture lists.
11. The method of claim 10 , wherein the MVPs include the MVPL0 for L0 prediction and the MVPL1 for L1 prediction,
the MVL0 is derived based on a sum of the MVDL0 and the MVPL0, and
the MVL1 is derived based on a sum of the MVDL1 and the MVPL1.
12. The method of claim 10 , wherein the prediction related information includes information on symmetric motion vector differences, and
when the symmetric motion vector difference reference index L0 and the symmetric motion vector difference reference index L1 are derived based on picture order count (POC) differences between the short-term reference pictures and a current picture including the current block, the value of the information on the symmetric motion vector differences is 1.
13. The method of claim 10 , wherein the size of the MVDL1 is the same as that of the MVDL0, and
the sign of the MVDL1 is opposite to that of the MVDL0.
14. The method of claim 10 , wherein the short-term reference pictures include short-term reference picture L0 and short-term reference picture L1,
the symmetric motion vector difference reference index L0 indicates the short-term reference picture L0, and
the symmetric motion vector difference reference index L1 indicates the short-term reference picture L1.
15. The method of claim 14 , wherein the reference picture lists include reference picture list 0,
the reference picture list 0 includes the short-term reference picture L0, and
the symmetric motion vector difference reference index L0 is derived based on picture order count (POC) differences between each of short-term reference pictures included in the reference picture list 0 and a current picture including the current block.
16. The method of claim 15 , wherein the symmetric motion vector difference reference index L0 is derived based on comparison between the POC differences.
17. The method of claim 16 , wherein the reference picture list 0 further includes another short-term reference picture L0,
the POC differences include a first POC difference between the short-term reference picture L0 and the current picture and a second POC difference between another short-term reference picture L0 and the current picture, and
the first POC difference is smaller than the second POC difference.
18. A non-transitory computer readable storage medium storing a bitstream generated by a method, wherein the method comprising:
deriving an inter prediction mode for a current block;
constructing motion vector predictor (MVP) candidate lists for the current block based on neighboring blocks of the current block;
deriving MVPs for the current block based on the MVP candidate lists;
generating prediction related information including information on the inter prediction mode and motion vector differences (MVDs) for the current block;
deriving motion information for the current block based on the information on the MVPs and the MVDs;
generating predicted samples for the current block based on the motion information;
generating residual information based on the predicted samples; and
encoding image information including the prediction related information and the residual information to output the bitstream,
wherein the motion information includes motion vectors (MVs) and symmetric motion vector difference reference indices,
wherein the MVs include MVL0 for L0 prediction and MVL1 for L1 prediction,
wherein the symmetric motion vector difference reference indices include the symmetric motion vector difference reference index L0 for L0 prediction and the symmetric motion vector difference reference index L1 for L1 prediction,
wherein the information on the MVDs includes the information on the MVDL0 for L0 prediction,
wherein the information on the MVDL1 for L1 prediction is derived based on the information on the MVDL0,
wherein the MVL0 is derived based on the information on the MVDL0,
wherein the MVL1 is derived based on the information on the MVDL1,
wherein the symmetric motion vector difference reference index L0 and the symmetric motion vector difference reference index L1 are derived based on short-term reference pictures among reference pictures included in reference picture lists.