结合全色度HEVC和有损字典算法的屏幕图像编码

Screen Content Coding of Combining Full-chroma HEVC and Lossy Matching Dictionary Coder

鉴于传统视频压缩算法对屏幕视频编码的效果不理想,提出了一种误差限自适应的有损字典编码方案,并和全色度HEVC有机融合,形成LDSC（Lossy Dual-coder Single Chroma-sampling-rate）算法.该算法根据屏幕内容中不同类型区域的编码特性,自适应地选择率失真性能较好的编码结果放入码流.为了评价有损字典编码的性能,提出了基于匹配长度和匹配失真的LD-Cost（Length Distortion Cost）模型,并使用拉格朗日乘子法对模型进行分析和计算.对于有损字典编码过程中可能出现的误差积累现象,给出了可行的解决方案.实验结果表明,与基于无损字典编码的双编码器方案相比,在不损伤主观图像质量的前提下,LDSC算法能明显提高编码性能,对连续色调内容居多的屏幕视频也表现出更好的编码适应性,全Ⅰ帧配置下BD-rate性能比基于无损字典编码的方案提高了3％～15％,与单纯使用HEVC相比,BD-rate性能提高了7％～49％.

Since traditional video compressing tools are not suitable for screen contents,a lossy dictionary coding algorithm with adaptive matching error limit was proposed.After combining with full-chroma HEVC,a dual-coder scheme named LDSC（Lossy Dual-coder Single Chroma-sampling-rate） was obtained.According to the coding character of different types of area in screen content,better coding result was selected adaptively and put into bit-stream.To evaluate the performance of lossy string matching,we proposed the LD-Cost model based on the string matching length and distortion by employing lagrangian multiplier method.We also gave an elaborate analysis about the error accumulation phenomenon during lossy dictionary coding and pointed out a feasible way to avoid it.Experimental reault show that the proposed method can obviously improve coding efficiency comparing with lossless dictionary coder based dual-coder scheme,and has betteradaptability when coding discontinues-tone area of screen content.3 ％ ～ 15 ％ coding gain can be achieved in BD-rate against lossless dictionary coder based dual-coder scheme in all-intra configuration.And the proposed method can obtain more BD-rate performance improvement,compared with latest HEVC reference software.