Screen Content Coding by Combined Full-chroma LZMA and Subsampled-chroma HEVC

Considering the anisotropic characteristics of screen content, satisfactory coding efficiency cannot be achieved when screen content is coded only by traditional image/video coding tools. A new Dual-coder Mixed Chroma-sampling-rate (DMC) technique is proposed for full-chroma (YUV4:4:4) screen content coding by adding a dictionary-entropy based coder which extracted from Lempel-Ziv-Markov chain Algorithm (LZMA) to existing High Efficiency Video Coding (HEVC) SDK tools for better coding efficiency of discontinues-tone portion of screen content. Two coders are seamlessly unified and the optimal coder is selected adaptively macroblock-by-macroblock to fit the characteristics of the macroblock content. A mixed chroma-sample-rate method is also proposed for reducing distortions to convert YUV4:4:4 to YUV4:2:0. Coding experimental results show that DMC coding can achieve much higher PSNR than the current HEVC. There are also obvious improvements on the subjective visual quality differences between them.