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Research On Rate-distortion Optimization For HEVC Video Coding

Posted on:2016-12-17Degree:MasterType:Thesis
Country:ChinaCandidate:Q WanFull Text:PDF
GTID:2428330473964837Subject:Computer technology
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High Efficiency Video Coding(HEVC)is a new generation of video coding standard for diversified video application and high-resolution video encoding.HEVC adopts many new coding techniques,which include a quadtree-based coding unit division,more flexible intra-prediction modes.Compared with previous video coding standard H.264/AVC,HEVC improves the compression ratio by about 50% at the same visual quality.However,it is at the sacrifice of significant increase of computational complexity.HEVC adopts rate-distortion optimization(RDO)technique to compromise between the bitrate and distortion,which d etermines the division of coding unit and the optimal prediction mode.Therefore,RDO is the key factor of HEVC,which has influence on both visual quality and compression efficiency.In this thesis,we research on the RDO techniques for HEVC video coidng so as to decrease the computation complexity and improve the bitrate-distoriton performance.Specifically,the main research works and contributions are summarized as follows.First,to address the huge computational complexity of intra prediction coding in the RDO process of HEVC,a quantized coefficients-based bitrate and distortion estimation apprach is proposed for efficient RDO framework.By estimating the bitrate and distortion of the quantized DCT coefficients,some steps in the standard RDO framework such as entropy coding,inverse quantization and inverse transform can be skipped,which significantly reduces the computational complexity.Moreover,Sobel operator is used to calculate the gradient value of image edges.The sum of gradient vectors in a prediction unit(PU)is used to select the optimal candidate mode within the candidate mode set.Thus,the huge computational complexity due to too many candidate modes can be greatly reduced.Experimental results show that the proposed method can greatly reduce the computational complexities of rate distortion optimization and intra prediction of HEVC.Second,a novel distortion estimation approach is proposed for the RDO process of HEVC by combining the structure similarity index(SSIM)and sum of squar ed error(SSE).The existing RDO approaches usually utilize SSE as distoriton estimator,which does not always match the perceived video quality of human visual system.By combining SSE and SSIM and introducing them into the RDO process,the superior performance of SSE in estimating the distortion in complex texture region and the computational simplicity of SSE in estimating the distortion in smooth region are balanced,which further improves the perceptual video quality after encoding.Moreover,considering that the quantization parameter(QP)might be different for each coding unit in HEVC,a Lagrange multiplier approach is proposed based on the optimal QP.It can made better trade-off between bitrate and distortion.Experimental results show that the proposed model can achieve better rate-distortion performance and provide better visual quality than those traditional RDO approaches.
Keywords/Search Tags:High Efficiency Video Coding(HEVC), Rate-distortion Optimization(RDO), Structural Similarity(SSIM)Index, Intra Prediction, Distortion Estimator, Quantized Coeffcient
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