A fast CU size decision algorithm for the HEVC intra encoder

Intra coding plays a crucial role in the High Efficiency Video Coding (HEVC) standard. It provides the higher coding efficiency than the previous standard, H.264/Advanced Video Coding. The block partitioning in HEVC supports quad-tree-based coding unit (CU) structure from size 64 × 64 to 8 × 8. The new technique provides better performances on one hand, whereas on the other hand it also increases the coding complexity. In this paper, a novel fast algorithm is proposed for the CU size decision in intra coding. Both the global and local edge complexities in horizontal, vertical, 45° diagonal, and 135° diagonal directions are proposed and used to decide the partitioning of a CU. Coupled with handling its four sub-CUs in the same way, a CU is decided to be split, nonsplit, or undetermined for each depth. Compared with the reference software HM10.0, the encoding time is reduced by ∼52% on average, with ∼0.8% Bjontegaard Distortion-rate increasing and reasonable peak signal-to-noise ratio losses.