Two stage fast mode decision algorithm for intra prediction in HEVC

Abstract

High efficiency video coding (HEVC) standard, introduced by the joint collaborative team on video coding (JCT-VC), is the newest international standard for video compression. This standard provides more compression and better video quality, compared with the previous standards such as H.264/AVC. The higher compression efficiency in HEVC is achieved at the cost of increasing the computational load. Intra prediction unit is among the high computational stages in the HEVC encoder. There are proposed 35 intra prediction modes in HEVC, to improve the compression efficiency. To reduce the computational load of intra prediction, HEVC uses a preprocessing step, called Rough Mode Decision (RMD). A number of best prediction modes are selected by the RMD stage and then, using Rate Distortion Optimization (RDO) process, the encoder selects the best prediction mode among them. In this paper a two stage algorithm is proposed for fast intra mode decision in HEVC encoder, in the first stage of our proposed algorithm the number of the tested modes in RMD is reduced from 35 to 19. In the second stage, the number of the tested modes in the RDO process is reduced as well. In order to evaluate the performance of the proposed method two encoding profiles, main and main10 were used in the experiments. Experimental results indicate that the proposed method achieves 14.4 and 7.2 % reduction in the encoding time compared with the HEVC reference software in all intra-main and all intra-main10 configurations, respectively. Meanwhile, it imposes minimum reduction in the coding efficiency among the compared methods.