The Research On Pre-processing Methods And Motion Estimation Algorithms For Video Coding

With the rapid development of modern digital communication technology and the extensive applications of HDTV, Net Video and DVD, video coding techniques are highly regarded now. As an important branch of computer multimedia technologies, video coding is becoming a focus of academic research all over the world.The goal of digital video compression is using fewer bits to represent video stream.And at the same time it should keep the subjective quality of the compressed video good, and make it satisfy specific applications. Thus, to find more efficient schemes which can improve compression rate and visual quality with lower coding complexities is always the goal of video coding research.Based on the research of the development and basic techniques of video coding, the thesis focuses on video pre-processing methods and motion estimation algorithms.The main achievements of this thesis include:1. Pre-processing methods for video compression.For the video signal, human eyes are the final receivers, thus video compression should consider the effect of human visual system. As the ability of human eyes is limited, it is hard to detective some distortions.Thus, if the distortion can be tolerated by human eyes or it can satisfy some applications, video codec can allow certain distortions to appear in the reconstructed images. Before compression and transmission, we can take advantage of the characters of HVS to pre-process original video sequences, and then encode and transmit them. Experimental results show that the proposed algorithm can improve compression ratio to a great extend without sacrificing subjective video subjective quality, and at the same compression rate, the subjective video quality using pre-processing technique is obviously better than that of the original compression scheme.2. Fast search algorithms for block-matching motion estimation.As a key part of video coder, motion estimation is extremely complicated and time-consuming.Thus an efficient motion estimation algorithm is always essential to the research of real-time video coding and decoding.Based on adaptive rood pattern search (ARPS) algorithm, a new fast and efficient motion estimation algorithm called enhanced adaptive rood pattern search (E-ARPS) is proposed in this thesis. Four aspects are proposed to improve ARPS: utilize spatial correlations to predict the initial search centre, introduce a new initial search based on motion vector (MV) centre-biased distribution, adopt a new adaptive unequal-arm rood search pattern and incorporate early terminations. Experimental results show that our algorithm has yielded significant search efficiency gain while consistently ensure search accuracy. Based on the study of the principle of the UMHexagonS algorithm, a new adaptive unsymmetrical-cross pattern is adopted instead of the unsymmetrical-cross proposed in the UMHexagonS. In JM10.2, experimental results show that the improved UMHexagonS algorithm can effectively reduce motion estimation duration and improvethe quality of the reconstructed images compared with the original performance of the UMHexagonS algorithm.