Adaptive weighting of reference pictures in video encoding

1. A video encoder for encoding video signal data for an image block, the encoder comprising a reference picture weighting factor assignor for assigning a weighting factor for the image block, the weighting factor being associated with a particular reference picture index, wherein the particular reference picture index is for independently indicating, without use of another index, a reference picture from which the image block is predicted and the weighting factor from a set of weighting factors.

2. A video encoder as defined in claim 1 , further comprising a reference picture store in signal communication with the reference picture weighting factor assignor for providing the reference picture corresponding to the particular reference picture index.

3. A video encoder as defined in claim 1 , further comprising a variable length coder in signal communication with the reference picture weighting factor assignor for providing the particular reference picture weighting factor to the variable length coder.

4. A video encoder as defined in claim 1 , further comprising a motion compensation unit in signal communication with the reference picture weighting factor assignor for providing motion compensated reference pictures responsive to the reference picture weighting factor assignor.

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

6. A video encoder as defined in claim 5 usable with bi-predictive picture predictors, the encoder further comprising prediction means for forming first and second predictors from two different reference pictures.

7. A video encoder as defined in claim 6 wherein the two different reference pictures are both from the same direction relative to the image block.

8. A method for encoding video signal data for an image block, the method comprising:

receiving an uncompressed image block;

assigning a weighting factor for the image block, the weighting factor being associated with a particular reference picture index, wherein the particular reference picture index is for independently indicating, without use of another index, a particular reference picture from which the image block is predicted and the weighting factor from a set of weighting factors;

computing motion vectors corresponding to the difference between the image block and the particular reference picture;

motion compensating the particular reference picture in correspondence with the motion vectors;

modifying the motion compensated reference picture by the assigned weighting factor to form a weighted motion compensated reference picture;

comparing the weighted motion compensated reference picture to the uncompressed image block; and

encoding a signal indicative of the difference between the uncompressed image block and the weighted motion compensated reference picture along with the reference picture index of the particular reference picture.

9. A method as defined in claim 8 wherein computing motion vectors comprises:

testing within a search region for every displacement within a pre-determined range of offsets relative to the image block;

calculating at least one of the sum of the absolute difference and the mean squared error of each pixel in the image block with a motion compensated reference picture; and

selecting the offset with the lowest sum of the absolute difference and mean squared error as the motion vector.

10. A method as defined in claim 8 wherein bi-predictive picture predictors are used, the method further comprising:

assigning a second weighting factor for the image block corresponding to a second reference picture index corresponding to a second reference picture;

computing motion vectors corresponding to the difference between the image block and the second reference picture;

motion compensating the second reference picture in correspondence with the motion vectors;

multiplying the motion compensated second reference picture by the assigned second weighting factor to form a weighted motion compensated second reference picture;

subtracting the weighted motion compensated second reference picture from the substantially uncompressed image block; and

encoding a signal indicative of the difference between the substantially uncompressed image block and the weighted motion compensated second reference picture along with the corresponding second reference picture index.

11. A method as defined in claim 10 wherein the two different reference pictures are both from the same direction relative to the image block.

12. A method as defined in claim 10 wherein computing motion vectors comprises:

testing within a search region for every displacement within a pre-determined range of offsets relative to the image block;

calculating at least one of the sum of the absolute difference and the mean squared error of each pixel in the image block with a first motion compensated reference picture corresponding to the first predictor;

selecting an offset with the lowest sum of the absolute difference and mean squared error as the motion vector for the first predictor;

calculating at least one of the sum of the absolute difference and the mean squared error of each pixel in the image block with a second motion compensated reference picture corresponding to the second predictor; and

selecting an offset with the lowest sum of the absolute difference and mean squared error as the motion vector for the second predictor.