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:
determining a number of available bi-prediction weights based at least in part on a temporal layer of a current picture in a hierarchical prediction structure, wherein the number of available bi-prediction weights decreases for increasing temporal layers;
from among the determined number of available bi-prediction weights, identifying a first weight and a second weight; and
predicting a current block in the current picture as a weighted sum of a first reference block in a first reference picture and a second reference block in a second reference picture, wherein the first reference block is weighted by the first weight and the second reference block is weighted by the second weight.
2. The method of claim 1 , wherein the number of available bi-prediction weights is further determined by a quantization parameter of the current picture, and wherein the number of available bi-prediction weights decreases for increasing quantization parameter.
3. The method of claim 2 , wherein, for at least one pair of values of the temporal layer of the current picture and the quantization parameter of the current picture, the determined number of available bi-prediction weights is one.
4. The method of claim 1 , wherein identifying the first weight and the second weight comprises parsing from a bitstream information identifying at least one of the first weight and the second weight.
5. An apparatus comprising a processor configured to perform at least:
determining a number of available bi-prediction weights based at least in part on a temporal layer of a current picture in a hierarchical prediction structure, wherein the number of available bi-prediction weights decreases for increasing temporal layers;
from among the determined number of available bi-prediction weights, identifying a first weight and a second weight; and
predicting a current block in the current picture as a weighted sum of a first reference block in a first reference picture and a second reference block in a second reference picture, wherein the first reference block is weighted by the first weight and the second reference block is weighted by the second weight.
6. The apparatus of claim 5 , wherein the number of available bi-prediction weights is further determined by a quantization parameter of the current picture, and wherein the number of available bi-prediction weights decreases for increasing quantization parameters.
7. The apparatus of claim 6 , wherein, for at least one pair of values of the temporal layer of the current picture and the quantization parameter of the current picture, the determined number of available bi-prediction weights is one.
8. The apparatus of claim 5 , wherein the apparatus is a video encoder.
9. The apparatus of claim 5 , wherein the apparatus is a video decoder.
10. A video encoding method comprising:
determining a number of available bi-prediction weights based at least in part on a temporal layer of a current picture in a hierarchical prediction structure, wherein the number of available bi-prediction weights decreases for increasing temporal layers;
from among the determined number of available bi-prediction weights, identifying a first weight and a second weight; and
predicting a current block in the current picture as a weighted sum of a first reference block in a first reference picture and a second reference block in a second reference picture, wherein the first reference block is weighted by the first weight and the second reference block is weighted by the second weight.
11. The method of claim 10 , wherein the number of available bi-prediction weights is further determined by a quantization parameter of the current picture, and wherein the number of available bi-prediction weights decreases for increasing quantization parameter.
12. The method of claim 11 , wherein, for at least one pair of values of the temporal layer of the current picture and the quantization parameter of the current picture, the determined number of available bi-prediction weights is one.
13. The method of claim 10 , further comprising signaling in a bitstream information identifying at least one of the first weight and the second weight.