Novel Adaptive Algorithm for Intra Prediction With Compromised Modes Skipping and Signaling Processes in HEVC

Up to 35 intra prediction modes are available for each Luma prediction unit in the coming HEVC standard. This can provide more accurate predictions and thereby improve the compression efficiency of intra coding. However, the encoding complexity is thus increased dramatically due to a large number of modes involved in the intra mode decision process. In addition, more overhead bits should be assigned to signal the mode index. Intuitively, it is not necessary for all modes to be checked and signaled all the time. Therefore, a novel adaptive modes skipping algorithm for mode decision and signaling processing is presented in this paper. More specifically, three optimized candidate sets with 1, 19, and 35 intra prediction modes are initiated for each prediction unit in the proposed algorithm. Based on the statistical properties of the neighboring reference samples used for intra prediction, the proposed algorithm is able to adaptively select the optimal set from the three candidates for each prediction unit preceding the mode decision and signaling processing. As a result, the mode decision process can be speeded up due to some modes skipping in the first two sets, and importantly less bits are required to signal the mode index. Experimental results show that, compared to the test model HM7.0 of HEVC, BD-Rate savings of 0.18% and as well as 0.18% on average are achieved for AI-Main and AI-HE10 cases for low-bitrate ranges, and the average encoding times can also be reduced by 8%-38% and 8%-34% for AI-Main and AI-HE10 cases in low-bitrate ranges, respectively.