环路内重映射带来的编码增益分析
Analysis of Coding Gain Due to In-Loop Reshaping
AI总结：
本文针对视频编码中的环路内重映射技术开展理论与实验研究，证明熵编码器次优时该技术可提升编码效率，推导出PSNR增益闭式解且与标准测试序列实验结果吻合。
摘要：
重映射是一种改变信号特性的点操作，已在视频编码实践中被证明能够提升压缩比。直接修改输入视频信号的环路外重映射最早被用作HEVC/H.265的补充增强信息（SEI），无需改动视频编解码器的核心设计。VVC/H.266进一步采用了对混合编码环路中处理的残差信号进行修改的环路内重映射，以提升编码效率。本文对环路内重映射的率失真性能进行了理论分析，并通过实验验证了理论结果。我们证明，当编码流程中采用的熵编码器为次优时——这与视频编解码器运行的实际场景相符——环路内重映射能够提升编码效率。我们推导出了闭式表达的PSNR增益，并表明理论预测的增益与使用标准测试视频序列实验测得的增益一致。
英文摘要：
Reshaping, a point operation that alters the characteristics of signals, has been shown capable of improving the compression ratio in video coding practices. Out-of-loop reshaping that directly modifies the input video signal was first adopted as the supplemental enhancement information (SEI) for the HEVC/H.265 without the need to alter the core design of the video codec. VVC/H.266 further improves the coding efficiency by adopting in-loop reshaping that modifies the residual signal being processed in the hybrid coding loop. In this paper, we theoretically analyze the rate-distortion performance of the in-loop reshaping and use experiments to verify the theoretical result. We prove that the in-loop reshaping can improve coding efficiency when the entropy coder adopted in the coding pipeline is suboptimal, which is in line with the practical scenarios that video codecs operate in. We derive the PSNR gain in a closed form and show that the theoretically predicted gain is consistent with that measured from experiments using standard testing video sequences.
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