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Mixed Chroma Sampling-Rate High Efficiency Video coding for Full-Chroma Screen Content

IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY 2013年第1期23卷 173-185页

作者： Lin, Tao Zhang, Peijun Wang, Shuhui Zhou, Kailun Chen, Xianyi Tongji Univ VLSI Lab Shanghai 200092 Peoples R China

Computer screens contain discontinuous-tone content and continuous-tone content. Thus, the most effective way for screen content coding (SCC) is to use two essentially different coders: a dictionary-entropy coder and a traditional hybrid coder. Although screen content is originally in a full-chroma (e. g., YUV444) format, the current method of compression is to first subsample chroma of pictures and then compress pictures using a chroma-subsampled (e. g., YUV420) coder. Using two chroma-subsampled coders cannot achieve high-quality SCC, but using two full-chroma coders is overkill and inefficient for SCC. To solve the dilemma, this paper proposes a mixed chroma sampling-rate approach for SCC. An original full-chroma input macroblock (coding unit) or its prediction residual is chroma-subsampled. One full-chroma base coder and one chroma-subsampled base coder are used simultaneously to code the original and the chroma-subsampled macroblock, respectively. The coder minimizing rate-distortion (R-D) is selected as the final coder for the macroblock. The two base coders are coherently unified and optimized to get the best overall coding performance and share coding components and resources as much as possible. The approach achieves very high visual quality with minimal computing complexity increment for SCC, and has better R-D performance than two full-chroma coders approach, especially in low bitrate.

关键词： dictionary-entropy coding full-chroma hybrid coding screen content coding

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United coding method for compound image compression

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MULTIMEDIA TOOLS AND APPLICATIONS 2014年第3期71卷 1263-1282页

作者： Wang, Shuhui Lin, Tao Tongji Univ VLSI Lab Shanghai 200092 Peoples R China

This paper proposes a compound image coding method named united coding (UC). In UC, several lossless coding tools such as dictionary-entropy coders, run-length encoding (RLE), Hextile, and a few filters used in portable network graphics (PNG) format are united into H.264 like intraframe hybrid video coding. The basic coding unit (BCU) has a size typically between 16 x 16 pixels to 64 x 64 pixels. All coders in UC are used to code each BCU. Then, the lossless coder that generates minimum bit-rate (R) is chosen as the optimal lossless coder. Finally, the final optimal coder is chosen from the lossy intraframe hybrid coder and the optimal lossless coder using R-D cost based optimization criterion. Moreover, the data coded by one lossless coder can be used as the dictionary of other lossless coders. Experimental results demonstrate that compared with H.264, UC achieves up to 20 dB PSNR improvement and better visual picture quality for compound images with mixed text, graphics and natural picture. Compared with lossless coders such as gzip and PNG, UC can achieve 2-5 times higher compression ratio with just a minor loss and keep partial-lossless picture quality. The partial-lossless nature of UC is indispensable for some typical applications, such as cloud computing and rendering, cloudlet-screen computing and remote desktop, where lossless coding of partial image regions is demanded. On the other hand, the implementation complexity and cost increment of UC is moderate, typically less than 25 % of a traditional hybrid coder such as H.264.

关键词： Compound image and video United coding Hybrid coding Lossless coding dictionary-entropy coding

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