Adaptive Intra Candidate Selection With Early Depth Decision for Fast Intra Prediction in HEVC

To better exploit spatial correlations in a video frame, the High Efficiency Video Coding (HEVC) standard has adopted a great many more intra prediction modes than H.264/AVC. As a result, the complexity of rate-distortion-optimized (RDO) HEVC intra mode selection is very high. Many techniques have been proposed to expedite the intra mode selection process to achieve a better overall tradeoff between complexity and RD performance. In this paper, two novel techniques for adaptive intra mode candidate selection and bidirectional depth search algorithms are utilized to accelerate intra prediction. The proposed techniques show an average of 63% (up to 67%) time saving with only 1% BD-Rate increase, outperforming most of existing intra prediction algorithms.

I. Introduction

The high efficiency video coding (HEVC) standard achieves about 50% bitrate reduction as compared with H.264/AVC [1], [2]. For intra prediction, HEVC supports up to 35 prediction modes and coding unit size from 4  4 to 64  64. As a result, the complexity of HEVC intra prediction is significantly higher than for H.264/AVC. To achieve good HEVC RD performance while lowering complexity, numerous algorithms have been proposed. Among the algorithms, some utilized various features of the current block for early termination of the RD mode decision process. Yet more algorithms simplified the rate-distortion optimized (RDO) process by replacing the RD cost by metrics such as the absolute transformed difference (SATD) that was easier to calculate. The rough mode decision (RMD) algorithm [3], [4] was adopted into the HEVC test model (HM) 2.0.