Referring to FIG. 4, the BIO assumes that an optical flow (+vx, +vy) for the first reference picture Ref0 and an optical flow (?vx, ?vy) for the second reference picture Ref1 have the same magnitude but different signs. Therefore, in order for the bidirectional motion vectors (MVx0, MVy0) and (MVx1, MVy1) to satisfy the BIO assumption, the x components MVx0 and MVx1 of the bidirectional motion vectors should have different signs, and the y components MVy0 and MVy1 should also have different signs. In addition, in order to satisfy the CVC condition, the absolute value of MVx0 divided by τ0, which is the time-domain distance between the current picture and the first reference picture, should be equal to the absolute value of MVx1 divided by τ1, which is the time-domain distance between the current picture and the second reference picture. Similarly, the absolute value of MVy0 divided by τ0 and the absolute value of MVy1 divided by τ1 should be equal to each other. Therefore, based on the concept of a threshold, the CVC condition as given above may be derived.
The BCC condition is satisfied when the SAD between the reference blocks that the bidirectional motion vectors (MVx0, MVy0) and (MVx1, MVy1) refer to, respectively, is less than or equal to a threshold TBCC. Of course, other indicators that may represent the difference between two reference blocks, such as SSE, may be used instead of SAD.
