The uni-prediction candidate list is derived directly from the merge candidate list constructed according to the extended merge prediction process in 3.4.1. Denote n as the index of the uni-prediction motion in the geometric uni-prediction candidate list. The LX motion vector of the n-th extended merge candidate, with X equal to the parity of n, is used as the n-th uni-prediction motion vector for geometric partitioning mode. These motion vectors are marked with “x” in Figure 38. In case a corresponding LX motion vector of the n-the extended merge candidate does not exist, the L(1 − X) motion vector of the same candidate is used instead as the uni-prediction motion vector for geometric partitioning mode.
Figure 38 – Uni-prediction MV selection for geometric partitioning mode
After predicting each part of a geometric partition using its own motion, blending is applied to the two prediction signals to derive samples around geometric partition edge. The blending weight for each position of the CU are derived based on the distance between individual position and the partition edge.
The distance for a position to the partition edge are derived as:
(3-0)
(3-0)
(3-0)
(3-0)
where are the indices for angle and offset of a geometric partition, which depend on the signaled geometric partition index. The sign of and depend on angle index .
The weights for each part of a geometric partition are derived as following:
(3-0)
(3-0)
(3-0)
The partIdx depends on the angle index . One example of weigh is illustrated in Figure 39.
