Research On HEVC Fast Intra Coding Algorithms Based On Quadtree Structure

In recent years, fast algorithms for HEVC have attracted more and more attention. In order to obtain higher coding efficiency, many new technologies are used in HEVC intra and inter coding, such as new coding mode, flexible coding structure and so on. Although HEVC obtains better compression than previous H.264, its computation load increases greatly. This in turn has negative effect on the coding rate. In order to achieve rapid coding rate and to meet application requirements, fast algorithms attract more attention. Fast algorithms can increase the coding rate while ensuring the coding efficiency. Mainly, fast algorithms include intra and inter fast coding algorithms. Aiming at the above problems, this thesis studies fast intra coding algorithms. The main contents and innovations are as follows:(1) HEVC intra coding includes the splitting process of coding unit(CU) and thirty-five modes selection process of prediction unit(PU). This thesis firstly studies the CU splitting process. HEVC employs flexible quadtree structure in this process. In this process, the rate distortion costs of CU from depth zero to depth three need calculating and then obtain the final splitting, which increases the computation amount. The thesis solves this problem by early terminating the splitting. It raises a parameter to represent the texture of CU and sets thresholds to early terminate the splitting. Besides, the thesis also analyzes the relationship between the depth of current coding unit and the surrounding coding units, and then uses this relationship to early terminate the splitting.(2) The thesis analyzes the thirty-five modes selection process of HEVC intra coding. In this process, Hardmard values of these modes need calculating to roughly obtain the candidate modes, followed by adding most probable mode into candidate modes and then compute rate-distortion values of candidate modes. The best mode is the one with least rate-distortion value. Aiming at this complexy process, this paper decreases the computation by decreasing the number of prediction modes in the rough mode decision process. This paper improves jiang’s fast algorithm, which based on gradient. This paper counts the edge direction of each 2x2 block to obtain the current edge direction of PU, which decreases the the number of candidate modes.(3) Based on the above studies, the thesis further analyzes the relationship between the CU splitting process and the PU mode decision process. It combines the study of this two processes and proposes two corresponding fast algorithms respectively.The thesis provides detailed experimental results and analyses. According to the experimental results, the proposed algorithms can effectively improve the coding rate while ensuring the coding efficiency. These results fully verify the correctness of above work.Finally, the thesis summarizes the whole work and provides discuss for further study.