A Fast Local Mode Decision for the HEVC Intra Prediction Based on Direction Detection

This work presents a fast local mode decision for the HEVC intra prediction based on a direction detection algorithm first proposed in the Daala video format and currently used in the AV1 deringing filter. The main objective is to reduce the number of intra candidates entering the very expensive RDO loop by locally detecting the dominant edge direction of the original block, without the need of computing any of the intra prediction modes and associated RD costs. The proposed method was implemented on the latest HEVC reference encoder (HM 16.20), replacing the original local mode decision by the algorithm proposed in this paper. Experiments under the HEVC common test conditions, including UHD 4K (3840x2160 pixels) test sequences, showed, on average, 28.2% encoding time reduction, at a cost of 1.0% BD-BR (YUV) increase. Specifically for UHD 4K sequences, the experiments showed, on average, 30.0% encoding time reduction, at cost of 0.9% BD-BR (YUV) increase.