Fast intra mode decision and fast CU size decision for depth video coding in 3D-HEVC

3D-HEVC is the new coding standard for both texture and associated depth video. In addition to several new coding tools that are designed for texture video with improved coding efficiency, some tools are specified for depth video, such as depth modeling modes (DMMs), segment-wise DC (SDC) mode and depth intra skip mode. This paper proposes techniques that accelerate the encoding of depth video, including a fast intra mode decision and a fast CU size decision. A hierarchical mode decision is proposed for the fast intra mode decision, based on a statistical analysis of mode distribution. The intra mode can be predicted at a very early stage if the hierarchical comparison of the rate-distortion (R-D) cost for selected candidate modes is satisfied for a given condition. For the fast CU size decision, smaller CU sizes are not evaluated if the current CU has the desired properties. The CU size of the collocated texture is also considered to avoid over-splitting of the current depth CU. The experimental results show that the proposed techniques achieve an average 62.5% time saving with 0.81% increase in the bitrate for the synthesized views under the all intra configuration, compared with the reference software HTM 15.0.