Research On High Efficiency Video Coding

As the age of big data concentration for information is coming, the problems of transmitting, storing and processing efficiently mass data of ultra/high-definition(HD/ UHD) and 3D video are needed to be solved immediately. In order to substantially improve the coding efficiency of the H.264/AVC video coding, a Joint Collaborative Team on Video Coding(JCT-VC) from ITU-T and ISO/IEC was formed for the development of a new international standard, so-called High Efficiency Video Coding(HEVC). And a 3D video extension of HEVC standard known as 3D-HEVC has been initially formed. Similar to H.264, HEVC adopts the conventional block-based hybrid video coding frame work, and offers many more flexible and advance technologies by introducing quadtree block segmentation, DST/DCT transform and so on. Based on HEVC, 3D-HEVC develops multi-view plus depth video coding system by further introducing the depth information which reflects the distance between the object and the camera.The standards HEVC and 3D-HEVC improve the coding efficiency by introducing many new methods, but there are still some places need to be optimized. Aiming to further enhance the coding performance of HEVC and 3D-HEVC standard, we study on high efficiency video coding techniques for 2D and 3D video. The primary work of the thesis is as follow:1. HEVC video encoding optimization(1). Analysis and optimization of Intra prediction optimization and Joint Transform coding for HEVC. To predict the DC value more efficiently, we first simplify the generative process of DC prediction in HEVC. Experimental results demonstrate that about 0.02% BD-rate saving can be achieved with less complexity, under the All-Intra(AI) and Low Delay(LD) configurations. Then we analyze the Discrete Cosine Transform(DCT) and Discrete Sine Transform(DST) of HEVC, and through the experimental simulation analysis the coding performance between DST and Discrete Cosine Transform(DCT). Finally, we propose DST/DCT transform scheme based intra mode and optimize the transformational matrix of DCT based orthogonality. The experimental results justify effectiveness of our proposed schemes.(2). Rate Distortion Optimization(RDO). To optimize coding performance in the block-based hybrid coding architecture, RDO techniques are widely employed based on different levels ranging from frame-level to slice-level, to coding tree unit(CTU)-level, coding unit(CU)-level and prediction unit(PU)-level. However the dependency among groups of pictures(GOPs) has not been addressed. Through a statistical analysis of the reference dependency among GOPs under the Random-Access(RA) configuration in the HEVC standard, we then develop a GOP-level Lagrange multiplier optimization scheme to further enhance the coding performance. The experimental results justify effectiveness of our proposed scheme, where 0.7% BD-rate saving can be achieved on average with the RA configuration with a lower overall coding complexity, compared with the latest reference software HM 16.7 of HEVC standard.2. Optimization of Depth Modeling Modes in 3D-HEVC Depth Intra Coding(1). Enhanced prediction of Constant Partition Value(CPV) and Rate distortion optimization. In the development of 3D-HEVC, Depth Modeling Modes(DMMs) are introduced in depth intra coding to represent object edges in depth maps. With the DMMs, a depth block is approximated by partitioning the block into two non-rectangular regions using Wedgelet or Contour partition, where each region is represented by a constant value referred to as CPV. To predict the CPV more accurately and efficiently, we develop three approaches in this paper. First, a better CPV predictor may be obtained by simply extending the actual depth map boundary, which can also simplify the CPV prediction by removing comparisons and average operations. Second, we propose to choose an optimal combination of delta CPVs in terms of View Synthesis Optimization(VSO) at the encoder by checking more candidates. Finally, zero residual coding is suggested for DMMs coding units in the rate-distortion optimization loop. Experimental results demonstrate that about 0.2% and 0.1% BD-rate saving can be achieved on average for synthesized views with less complexity, under the AI and RA configurations, respectively.(2). Optimization of Wedgelet pattern segmentation(DMM-1). For a better representation of edges in depth maps, Depth Modeling Modes(DMMs) are added into depth intra prediction modes. The Explicit Wedgelet Signalization within DMM partitions the depth block into two non-rectangular regions by using a Wedgelet pattern selected from the Wedgelet lookup table. The Wedgelet lookup table is generated during both encoder and decoder initialization for each block size ranging from 4×4 to 16×16, and the Wedgelet lookup table stores a large number of Wedgelet patterns, which may cause cache storing problem or increase cache burden. In order to reduce the number of Wedgelet partitions in Wedgelet lookup table, we propose a rotation-sampling based method to remove the redundancy among different orientations and different block sizes. Specifically, a down-sampling method is employed to construct the 8×8 and 4×4 Wedgelet patterns so as to reduce the size of lookup table. Then, we remove the generation process of all Wedgelet patterns with some orientations by rotation. The experimental results show the down-sampling method can achieve storage size reduction by 27.8% with negligible 0.03% / 0.05% coding loss in both configurations of Common Test Conditions(CTC) and AI, respectively. Moreover, the rotation technique can achieve 0.04% / 0.03% BD-rate saving on average under AI / CTC. Generally, the proposed rotation-sampling based method can save storage size by 75.1% with no coding loss.(3). Optimization of Contour pattern segmentation(DMM-4). For Contour partition, the corresponding coded texture information of current depth block is employed to predict the final block partition. However, it just utilizes the structural similarity between texture and depth, without considering the edge similarity between adjacent boundary blocks within the same depth map, which may lead to inaccurate block partition, thereby affecting the coding efficiency. To address the problem above, an optimized Contour partition generation method, which makes full use of the edge similarity between adjacent boundary blocks, is proposed. The experimental results demonstrates nearly averaged 0.1% BD-rate saving can be achieved for synthesized views under all intra case, compared with the reference software HTM 11.0.