Generalized bi-prediction for video coding with reduced coding complexity
Exemplary embodiments include systems and methods for coding a video comprising a plurality of pictures including a current picture, a first reference picture, and a second reference picture, where each picture includes a plurality of blocks. In one method, for at least a current block in the current picture, a number of available bi-prediction weights is determined based at least in part on a temporal layer and/or a quantization parameter of the current picture. From among available bi-prediction weights a pair of weights are identified. Using the identified weights, the current block is then predicted as a weighted sum of a first reference block in the first reference picture and a second reference block in the second reference picture. Encoding techniques are also described for efficient searching and selection of a pair of bi-prediction weights to use for prediction of a block.
1. A video decoding method comprising:
for a current block, obtaining a first temporal distance to a first reference picture and a second temporal distance to a second reference picture;
selecting at least a first weight value from among a plurality of weights in a first predetermined set of weights, the first predetermined set of weights being selected based at least in part on a comparison of the first temporal distance and the second temporal distance; and
predicting the current block as a weighted sum of a first reference block in the first reference picture and a second reference block in the second reference picture, wherein the first reference block is weighted by the first weight and the second reference block is weighted by a second weight.
2. The method of claim 1 , wherein the first predetermined set of weights is a set of no more than seven weights.
3. The method of claim 1 , wherein the first predetermined set of weights is a set of no more than four weights.
4. The method of claim 1 , wherein the first predetermined set of weights is a set of four weights.
5. The method of claim 1 , wherein the second weight is selected from among a plurality of weights in a second predetermined set of weights different from the first predetermined set of weights.
6. The method of claim 2 , wherein the second weight is obtained by subtracting the first weight from one.
7. A video decoding apparatus comprising a processor configured to perform at least:
for a current block, obtaining a first temporal distance to a first reference picture and a second temporal distance to a second reference picture;
selecting at least a first weight value from among a plurality of weights in a first predetermined set of weights, the first predetermined set of weights being selected based at least in part on a comparison of the first temporal distance and the second temporal distance; and
predicting the current block as a weighted sum of a first reference block in the first reference picture and a second reference block in the second reference picture, wherein the first reference block is weighted by the first weight and the second reference block is weighted by a second weight.
8. The apparatus of claim 7 , wherein the first predetermined set of weights is a set of no more than seven weights.
9. The apparatus of claim 7 , wherein the first predetermined set of weights is a set of no more than four weights.
10. The apparatus of claim 7 , wherein the first predetermined set of weights is a set of four weights.
11. The apparatus of claim 7 , wherein the second weight is selected from among a plurality of weights in a second predetermined set of weights different from the first predetermined set of weights.
12. The apparatus of claim 8 , wherein the second weight is obtained by subtracting the first weight from one.
13. A video encoding method comprising:
for a current block, obtaining a first temporal distance to a first reference picture and a second temporal distance to a second reference picture;
selecting at least a first weight value from among a plurality of weights in a first predetermined set of weights, the first predetermined set of weights being selected based at least in part on a comparison of the first temporal distance and the second temporal distance; and
predicting the current block as a weighted sum of a first reference block in the first reference picture and a second reference block in the second reference picture, wherein the first reference block is weighted by the first weight and the second reference block is weighted by a second weight.
14. The method of claim 13 , wherein the first predetermined set of weights is a set of no more than four weights.
15. The method of claim 13 , wherein the first predetermined set of weights is a set of four weights.
16. The method of claim 13 , wherein the second weight is selected from among a plurality of weights in a second predetermined set of weights different from the first predetermined set of weights.
17. A video encoding apparatus comprising a processor configured to perform at least:
for a current block, obtaining a first temporal distance to a first reference picture and a second temporal distance to a second reference picture;
selecting at least a first weight value from among a plurality of weights in a first predetermined set of weights, the first predetermined set of weights being selected based at least in part on a comparison of the first temporal distance and the second temporal distance; and
predicting the current block as a weighted sum of a first reference block in the first reference picture and a second reference block in the second reference picture, wherein the first reference block is weighted by the first weight and the second reference block is weighted by a second weight.
18. The apparatus of claim 17 , wherein the first predetermined set of weights is a set of no more than four weights.
19. The apparatus of claim 17 , wherein the second weight is selected from among a plurality of weights in a second predetermined set of weights different from the first predetermined set of weights.
20. The apparatus of claim 17 , wherein the second weight is obtained by subtracting the first weight from one.