An efficient early termination algorithm for depth coding is presented by considering the textureless characteristic of depth maps. In the proposed algorithm, all candidate modes are sorted in ascending order according to their inherent minimum rate-distortion costs (IMRDcost), resulting from the minimum number of head information coding bits. After finishing the rate-distortion cost (RDcost) calculation of each candidate mode, a termination decision will be made with IMRDcost of the next candidate mode to decide whether or not to terminate the mode decision process. Experimental results show that the algorithm can save encoding time by 84.20% on average, while the rate-distortion performance is invariant.Introduction: In the emerging three-dimensional video (3DV) data format-multi-view video plus depth (MVD), depth maps are used to synthesise virtual views with their corresponding texture images. The induction of depth maps enables the 3D and the free-viewpoint TV (FTV) applications, but it increases coding complexity extremely. Therefore, a faster depth coding algorithm is needed. Tsang et al. [1] proposed an efficient intra prediction algorithm by reducing the number of candidate prediction directions for smooth regions. In [2], the temporal and inter-view correlation of texture images was exploited to determine to skip some depth blocks at an early stage without a normal encoding process. Motion vector sharing and SKIP mode decision techniques were proposed in [3] to reduce the depth coding time by using the correlation between texture images and depth maps. Different from the algorithms mentioned above that reduce the intra prediction complexity only, or reduce the coding complexity with the associated texture images, in this Letter an efficient early termination algorithm for depth coding is proposed by considering the textureless characteristic of depth maps. With the proposed algorithm, the optimal mode can be found at an early stage during the rate-distortion optimisation (RDO) process with no extra coding loss being involved.
Rate-distortion optimisation (RDO) is the key technology that is used to choose the optimal coding parameters in video coding. As the Lagrangian multiplier plays a vital role in RDO, a model-based Lagrangian multiplier derivation method is proposed for depth map coding. This method is based on the analysis of the relationships among the Lagrangian multiplier, the coding distortion, the coding bitrate and the quantisation step. Experimental results demonstrate that the proposed method can achieve an average 3.42% bitrate saving compared with the method in HTM 16.0 reference software, and an average 0.41% bitrate saving compared with a state-of-art method.
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