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Local saliency detection based fast mode decision for HEVC intra coding

The High Efficiency Video Coding (HEVC) is the next generation video coding standard beyond H.264/AVC. Compared with only up to 9 modes for intra prediction in H.264/AVC, HEVC provides 35 intra prediction modes (IPM) to improve coding efficiency, which inevitably poses a huge complexity burden to the encoder. To speed up the HEVC encoder, a novel fast mode decision (FMD) algorithm for HEVC intra prediction is proposed. In the proposed algorithm, we analyzed the costs generated by rough mode decision (RMD), which has already been incorporated in the HM software. We found that the RMD costs listed by mode number generally follow the same trend with the rate-distortion optimization (RDO) costs. Further, the local salient modes, whose RMD costs have a significant drop compared with adjacent modes, tend to be promising competitors for the optimal mode. Based on these observations, we further reduced the number of the candidates for the RDO process. Experimental results show that our proposed algorithm achieves averagely 19.0% (up to 33.6%) encoding time saving whilst causing negligible RD performance loss (0.4% BD-Rate increase on average) compared with HM 7.0 anchor.