Adaptive weighting of reference pictures in video decoding

1. A video decoder for decoding video data for a picture having a plurality of image blocks, the decoder comprising:

a reference picture weighting factor unit for receiving at least one reference picture index, ones of the at least one reference picture index for independently indicating, without use of another index, one of a plurality of reference pictures from which a current one of the plurality of image blocks is predicted and a weighting factor from a set of weighting factors for the current one of the plurality of image blocks.

2. A video decoder as defined in claim 1 wherein the reference picture weighting factor unit has a second output for determining an offset corresponding to at least one of the at least one reference picture index.

3. A video decoder as defined in claim 1 , further comprising a variable length decoder in signal communication with the reference picture weighting factor unit for providing the at least one reference picture index to the reference picture weighting factor unit.

4. A video decoder as defined in claim 1 , further comprising a motion compensator in communication with the reference picture weighting factor unit for providing motion compensated reference picture predictors.

5. A video decoder as defined in claim 4 , further comprising a multiplier in communication with the motion compensator and the reference picture weighting factor unit for applying a weighting factor to a motion compensated reference picture predictor.

6. A video decoder as defined in claim 4 , further comprising an adder in signal communication with the motion compensator and the reference picture weighting factor unit for applying an offset to a weighted motion compensated reference picture predictor.

7. A video decoder as defined in claim 1 wherein the video data is streaming video data comprising block transform coefficients.

8. A video decoder as defined in claim 1 usable with bi-predictive picture predictors, the decoder further comprising:

prediction means for forming first and second predictors for an image block from two different reference pictures;

combining means for combining the first and second predictors together using their corresponding weighting factors to form a single combined predictor for the image block.

9. A video decoder as defined in claim 8 wherein the two different reference pictures are both from the same direction, forward direction or reverse direction, relative to the image block picture.

10. A method for decoding video data for a picture having a plurality of image blocks, the method comprising:

receiving a reference picture index with the data for a current image block, the index independently indicating, without use of another index, a reference picture from which the current image block is predicted and a weighting factor from a set of weighting factors for the current image block;

retrieving a motion compensated picture predictor using the indicated reference picture corresponding to the received reference picture index; and

varying the motion compensated reference picture predictor by the indicated weighting factor to form a weighted motion compensated reference picture predictor.

11. A method as defined in claim 10 , further comprising:

determining an offset corresponding to the received reference picture index; and

adjusting the weighted motion compensated reference picture predictor with the corresponding offset.

12. A method as defined in claim 10 , further comprising adding the weighted motion compensated reference picture predictor to the data for the image block to predict the image block.

13. A method as defined in claim 12 , further comprising storing the predicted image block as part of a picture for future retrieval.

14. A method as defined in claim 10 wherein the video data is streaming video data comprising block transform coefficients.

15. A method as defined in claim 10 wherein bi-predictive picture predictors are used, the method further comprising:

forming first and second predictors for an image block from two different reference pictures; and

combining the first and second predictors using their corresponding weighting factors to form a single predictor for the image block.

16. A method as defined in claim 15 , further comprising:

determining first and second offsets corresponding to each of the first and second predictors;

combining the first and second offsets to form a combined offset; and

combining the single predictor combined offsets to predict the image block.

17. A method as defined in claim 15 wherein the two different reference pictures are both from the same direction, forward direction or reverse direction, relative to the image block picture.

18. A program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform program steps for decoding video data for a picture having a plurality of image blocks, the program steps comprising:

receiving a reference picture index with the data for a current image block, the index independently indicating, without use of another index, a reference picture from which the current image block is predicted and a weighting factor from a set of weighting factors for the current image block;

retrieving a motion compensated picture predictor using the indicated reference picture corresponding to the received reference picture index; and

varying the motion compensated reference picture predictor by the indicated weighting factor to form a weighted motion compensated reference picture predictor.

19. A program storage device as defined in claim 18 , the program steps further comprising:

determining an offset corresponding to the received reference picture index; and

adjusting the weighted motion compensated reference picture predictor with the corresponding offset.

20. A program storage device as defined in claim 18 , the program steps further comprising adding the weighted motion compensated reference picture predictor to the data for the image block to predict the image block.