Fast Rate-Distortion Optimization for Depth Maps in 3-D Video Coding

To ensure the fidelity of virtual views, rate-distortion optimization (RDO) criterion for the 3D extension of the High Efficiency Video Coding (3D-HEVC) is well designed, in which the synthesized view distortion (SVD) is introduced to derive the rate-distortion (RD) cost. To obtain accurate SVDs, the rendering operation is employed which demands a fairly high computational complexity. To address this problem, a fast RDO method for depth maps is proposed, which checks the RD cost during its calculation process. Specifically, given a coding mode, the RD cost is composed of several cumulative items. If the accumulated RD cost is equal to or exceeds the minimum RD cost of previously coded modes, it will not be necessary to continue the RD cost calculation for the mode. To reduce the encoding complexity, existing methods usually aim at reducing the number of tested modes or block partitions. To the best of our knowledge, it is the first time that the latent redundant complexity in the RD cost calculation is investigated and removed. Experimental results demonstrate that, compared with the 3D-HEVC reference software, the proposed method can save 28.1% of depth coding time with a small coding gain (0.04% BD-rate saving). An additional test is designed to evaluate four typical fast coding methods with/without the proposed method. Extensive results verify that the proposed method can be seamlessly combined with the state-of-the-art methods.