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Rate-Distortion Control Techniques For Video Coding

Posted on:2011-06-23Degree:DoctorType:Dissertation
Country:ChinaCandidate:M LiFull Text:PDF
GTID:1118360305464262Subject:Communication and Information System
Abstract/Summary:PDF Full Text Request
Rate-distortion (R-D) theory is the fundamental theory of lossy compression techniques, which are widely employed in video and image compression schemes. For video applications, the R-D issues not only reveal the theoretical background for practical design of video coding systems, but also serve as the guidelines for improving the performance of video communication by providing high compression efficiency, successful network transmission of the coded data and acceptable visual quality at the receiver. In this thesis, the critical issues of rate-distortion based coder control are investigated, and several novel coder control approaches are proposed. The major contributions of this thesis are summarized as follows:1. The P-frames closer to the I-frames in a group of pictures (GOP) are directly or indirectly used as reference pictures for the successive coding frames. Therefore, the P-frames are always not equal in the importance to the entire coding quality of the GOP. Motivated by this feature, a quadratic curve based buffer management method is proposed and integrated in the recommended rate control scheme for H.264/AVC encoder, and the coding performance could be improved by unequally allocating the available bits among the P-frames in a GOP.2. Based on the analyses of the R-D properties of the foreground region and the background region of a video frame, a region-based rate control approach is developed and implemented in the macroblock (MB) layer. An adaptive factor is employed to properly assign more bits to the foreground MBs in the bit allocation phase. Then using the quadratic model with different parameters related to the two regions, the quantization parameter (QP) is computed and further adjusted according to the region information.3. An underlying rate control scheme is proposed for the hierarchical coding structure using hierarchical B-frames. Taking account of the coding characteristics of the hierarchical coding structure, a temporal level (TL) layer rate control phase is developed, and a typical weighting factor representing the TL coding characteristics is introduced in determining the target bits for the current coding B-frame. The frame layer QP is computed using the quadratic model with the corresponding model parameters of each TL, and then adaptively adjusted according to the usage of the target bit budgets.4. Based on the underlying rate control scheme proposed for the hierarchical coding structure, a QP determination method is proposed to adaptively determine the QPs for key frames. The QP for the first key frame in the sequence is calculated by an empirical expression which depicts the relationship of the starting QP, the available channel bandwidth and the source characteristics. For the other key frames, their QPs are firstly computed using an R-D model and then adjusted according to the reference QPs.5. Picture padding is introduced in H.264/AVC encoder to support the video coding at arbitrary resolution. From the perspective of coding efficiency and the concept of soft decision, we formulate the issue of R-D based picture padding as an optimization problem, and present an iterative solution which integrates the optimal picture padding in the R-D optimization (RDO) process. To reduce the related computational burden, a heuristic solution is proposed based on comprehensive analyses on the influence of the padded pixels on the encoder performance. This solution directly utilizes the already existing algorithms of RDO, and automatically implements the concepts and technologies of template matching and spatial extrapolation to determine the padded pixels, while keeping high coding performance and bringing little additional computational complexity to the codec.
Keywords/Search Tags:rate-distortion, rate control, rate-distortion optimization, hierarchical B-frame, arbitrary resolution video coding, H.264/AVC
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