Machine learning-based fast CU size decision algorithm for 3D-HEVC inter-coding

3D-high efficiency video coding (3D-HEVC) is an extension of the high efficiency video coding (HEVC) standard for the compression of the texture videos and depth maps. In 3D-HEVC inter-coding, the coding unit (CU) is recursively performed on variable sizes, namely, depth levels. The CU size decision process is conducted using all the possible depth levels to obtain the one with the least rate-distortion (RD) cost using the Lagrange multiplier. These tools achieve the highest coding efficiency but incur a very high computational complexity. In this paper, a fast CU size decision algorithm is proposed to reduce the complexity caused by the CU size splitting process. The proposed algorithm is based on the CU homogeneity classification using machine learning technology. First, the tensor feature is extracted to characterize the homogeneity of CU, which has a strong relationship with CU sizes. Then, a boosted decision stump algorithm is employed to analyze and construct a binary classification model from the extracted features and find suitable thresholds for the proposed method. Finally, an efficient early termination of CU splitting is released based on adaptive thresholds for texture videos and depth maps. The experimental results show that the proposed algorithm reduces a significant encoding time, while the loss in coding efficiency is negligible.