Method of predicting an image block
According to one embodiment of the method of determining a motion vector of a current image block at least a first motion vector of a current image block is determined based on a kind of reference buffer storing a reference picture referenced by a co-located image block. For example, in one embodiment of the method, a first motion vector of the current image block may be set equal to a motion vector of the co-located image block and a second motion vector of the current image block may be set equal to zero if the reference buffer is a kind of buffer storing a long-term reference picture.
1. A method of determining and using a motion vector of a current image block, the method performed by a moving picture coding system and comprising:
determining, by the moving picture coding system, a first motion vector of a current image block based on a kind of reference buffer storing a reference picture referenced by a co-located image block, the kind being one of long term and short term, the kind characterizing a temporal distance of the reference picture for the co-located image block with respect to the bi-predictive block, the determining step determining the first motion vector according to a first set of expressions if the reference buffer storing the reference picture is the short term kind and the determining step determining the first motion vector according to a second set of expressions if the reference buffer storing the reference picture is the long term kind, the second set of expressions being different than the first set of expressions; and
decoding, by the moving picture coding system, the current image block based on the determined first motion vector.
2. The method of claim 1 , wherein the second set of expressions sets the first motion vector of the current image block equal to a motion vector of the co-located image block if the reference buffer storing the reference picture is the long term kind.
3. The method of claim 2 , wherein the first motion vector is a forward motion vector.
4. The method of claim 2 , wherein the determining step is performed in a direct mode of operation.
5. The method of claim 2 , wherein the first set of expressions determines the first motion vector by scaling the motion vector of the co-located block if the reference buffer storing the reference picture is the short term kind.
6. The method of claim 5 , wherein the first motion vector is a forward motion vector.
7. The method of claim 5 , wherein the determining step is performed in a direct mode of operation.
8. The method of claim 1 , wherein
the second set of expressions sets the first motion vector of the current image block equal to a motion vector of the co-located image block and sets a second motion vector of the current image block equal to zero if the reference buffer storing the reference picture is the long term kind.
9. The method of claim 8 , wherein the determining step is performed in a direct mode of operation.
10. The method of claim 8 , wherein the current image block is a bi-predictive image block, the first motion vector is a forward motion vector, and the second motion vector is a backward motion vector.
11. The method of claim 8 , wherein the first set of expressions determines the first and second motion vectors of the current image block by scaling the motion vector of the co-located block if the reference buffer storing the reference picture is the short term kind.
12. The method of claim 1 , wherein the second set of expressions sets the first motion vector equal to zero if the reference buffer storing the reference picture is the long term kind.
13. The method of claim 12 , wherein the first motion vector is a backward motion vector.
14. The method of claim 12 , wherein the determining step is performed in a direct mode of operation.
15. The method of claim 12 , wherein the first set of expressions determines the first motion vector by scaling the motion vector of the co-located block if the reference buffer storing the reference picture is the short term kind.