位移(Offset)参数是帧内串复制(ISC)算法中复制参数的重要组成部分,用来表示当前待编码或解码像素串与参考像素串之间的位置关系.如何对Offset参数进行有效编码成为ISC算法中提高屏幕图像编码(SCC)效率的一个核心问题.为了消除现有Offset参数编码算法中的冗余,根据Offset参数的统计特性和找出Offset参数之间以及Offset参数与其他编码参数之间的相关性,提出了改进的Offset参数编码算法.该算法主要由Offset联合编码方案、水平扫描时OffsetX映射方案和截断2阶指数哥伦布编码方案组成.实验结果表明,对于SCC标准测试数据集中的视频序列,提出的Offset参数编码算法与现有的算法相比,在几乎没有增加编解码复杂度的前提下,对于全帧内(AI)、随机接入(RA)、低延迟(LB)3种编码配置,有损BD-rate平均降低率分别可达2.1％、1.5％、1.4％;无损Bit-rate总节省率分别可达1.8％、1.1％、1.1％,能有效提高编码效率.%Offset parameter is an important part of copy parameters in Intra String Copy (ISC) algorithm.Offset specifies the position displacement vector between the current string to be encoded or decoded and the reference string.In order to improve the coding efficiency of screen content,how to efficiently code the Offset parameters in ISC becomes a key issue.As the Offset parameters exhibit some unusual statistical characteristics and correlations between Offset parameters or correlations among Offset parameters and other coding parameters,there are some redundancies in existing Offset parameter coding algorithm.Therefore,an improved Offset parameters coding algorithm which consists of a joint Offset parameters coding scheme,an OffsetX mapping scheme in horizontal-scanned coding units,and a truncated 2th order Exp-Golomb binaryzation scheme is proposed in this paper to eliminate those redundancies.Compared with the existing Offset parameter coding algorithm,experimental results show that,for the HEVC SCC test sequences,the proposed algorithm achieves the BD-rate reduction up to 2.1％,1.5％,1.4％ for All Intra(AI),Random Access(RA) and Low-delay B (LB) configurations in lossy coding,respectively,the Bit-rate saving up to 1.8％,1.1％,1.1％ for AI,RA,LB configurations in lossless coding,respectively,at very little additional encoding or decoding complexity.
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