Gradient-Based Early Termination of CU Partition in VVC Intra Coding

The quaternary tree with nested binary and ternary tree structure is an efficient coding unit (CU) partitioning method adopted in Versatile Video Coding (VVC). Compared with quaternary tree only in HEVC, its flexible block sizes improve the coding performance significantly at the cost of computation load increase due to the recursive and nested searching for the best CU structure. In this paper, an early termination algorithm is proposed to skip unnecessary searches in CU size decision. Based on directional gradients, pre-determine the likelihood of binary partition or ternary partition in horizontal or vertical direction for current block, thus the impertinent partition pattern is skipped. The experimental results show that the proposed method is able to save the encoding time up to 51% with about 1.2% BD-rate degradation compared with VVC software reference VTM5.0.