Prediction Refinement with Optical Flow for Affine Motion Compensation

Affine motion compensation (AMC) has been adopted in the latest working draft of the Versatile Video Coding (VVC) standard jointly developed by ITU-T VCEG and ISO/IEC MPEG. The AMC in the VVC working draft is implemented as a sub-block based MC rather than pixel-based MC in order to reduce the memory access bandwidth and computation complexity, which loses prediction efficiency. The proposed algorithm in this paper is to improve the MC granularity by using pixel-based optical flow refinement. The affine prediction efficiency will be close to the pixel-based MC refinement without increasing external memory access. The experiment results show that on average the proposed algorithm can achieve 0.86% and 0.87% BD rate saving for random access and low delay B configurations, respectively, comparing to the VTM-4.0. The BD rate saving is up to 3.10%.