Geometry Partitioning with Motion Vector Difference for Video Coding

Geometric partitioning mode (GPM) is employed in the latest video coding standard known as versatile video coding (VVC). GPM provides a capability to partition an inter-coded block into two geometric regions with different motion vectors (MVs). However, MVs of the two partitions of a GPM coding unit (CU) are restricted to be selected from a MV candidate list, lacking the flexibility to refine the MVs. This paper presents a method named geometric partitioning with motion vector difference (GMVD). With the proposed GMVD mode, the MV of each GPM partition, partitioned by GPM, is generated as a sum of a base MV selected from a MV candidate list and a motion vector difference, signaled in a similar way as merge motion vector difference (MMVD) in VVC. The presented GMVD has been adopted into the enhanced compression model (ECM), developed by JVET to explore novel coding tools beyond VVC. Experimental results show that the presented GMVD provides an additional average luma BD-rate gain of 0.27% and 0.42% in RA and LB configurations over ECM-1.0 under the JVET CTC, with decent trade-off between compression efficiency and encoder complexity. Moreover, the decoder complexity of GMVD is negligible.