Early termination for fast intra mode decision in depth map coding using DIS-inheritance

Depth Intra Skip (DIS) mode is a new depth intra coding tool in the 3D extension of High Efficiency Video Coding (3D-HEVC) to improve the coding efficiency of depth maps. The optimization of quadtree partitioning in HEVC is conducted on different Coding Unit (CU) sizes from 64×64 to 8×8. Although all CU sizes should be considered in partition decision, only the CUs in the optimal partition structure are coded in the final bitstream. In this paper, it is found that the CUs well predicted by DIS (i) occupy a large proportion in mode decision; (ii) have a strong consistency in its sub-CUs at the higher depth level; and (iii) tend to be coded at the lower depth level in the final bitstream. Based on these observations, this work proposes an early termination scheme for fast intra mode decision in depth maps. Early termination of CU splitting is triggered according to the consistency of DIS between different depth levels by evaluating several most probable modes in the current CUs and its four sub-CUs based on the new distortion metric. Simulation results demonstrate that the proposed algorithm could save 31.04% of depth coding time with 0.07% increase in BDBR. By integrating with other fast intra mode decision methods, the overall algorithm could provide averagely 50.08% time reduction with only 0.64% increase in BDBR.