Coding unit splitting early termination for fast HEVC intra coding based on global and directional gradients

High efficiency video coding (HEVC) doubles the compression ratio as compared to H.264/AVC, for the same quality. To achieve this improved coding performance, HEVC presents a new content-adaptive approach to split a frame into coding units (CUs), along with an increased number of prediction modes, which results in significant computational complexity. To lower this complexity with intra coding, in this paper, we develop a new method based on global and directional gradients to terminate the CU splitting procedure early and prevent processing of unnecessary depths. The global and directional gradients determine if the unit is predicted with high accuracy at the current level, and where that's the case, the CU is deemed to be non-split. Experimental results show that the proposed method reduces the encoding time by 52% on average, with a small quality loss of 0.07 dB (BD-PSNR) for all-intra scenarios, as compared to the HEVC reference implementation, HM 15.0.