Research On The Key Technologies Of Screen Content Coding

Different from the camera-captured sequences,the screen content sequences are not limited to the physical structure of the camera,which contain no sensor noise.Moreover,screen content sequences always contain repeat patterns,large plat area and limited number of colors.To fully utilized these characteristics and improve the compression efficiency of the screen content sequences,HEVC-SCC standard was finalized in February 2016.HEVC-SCC standard introduced four screen content coding tools,these new coding tools can efficiently utilize different characteristics of screen content sequences and greatly improve the coding efficiency.However,the real-time transmission of screen content sequences is still a great challenge.Screen content sequences usually contain plenty of abrupt frames and static frames.The discontinuities in the sequences increase the difficulty of controlling the video bitrate after the compression by the SCC reference software.Moreover,introducing new tools to the encoder also increases the encoding complexity.Developing fast algorithms for the new tools has become a hot research topic.This dissertation focuses on the screen content coding in low delay video application,the main contributions are described as follow:This dissertation proposed a rate control scheme with delay constraint for screen content coding.To tackle the discontinuity is screen content sequences,a pre-analyzer is designed to analyze the complexity of incoming frames.The encoder will allocate bits for each frame according to the information gathered from the pre-analyzer.The pre-analyzer can help encoder make more rational bit allocation decisions during the rate control and avoid buffer overflow or underflow.However,introducing the pre-analyzer will increase the End-to-End transmission delay of the whole system.Therefore,this dissertation proposed a delay constraint condition which can manage the trade-off between buffer and pre-analyzer and avoid additional delay.Compared with the rate control scheme in HM16.7+SCM7.0,the proposed scheme can reduce 5.4%bitrate error and achieve 3.1 dB PSNR gain.The paper about proposed scheme has been accepted by the related academic conference and awarded as the best paper of that conference.This dissertation also proposed a graphics processing unit(GPU)based fast algorithm of palette mode in SCC.Since screen content sequences usually contain the coding blocks that have a small number of distinct colors.In palette mode,for each coding block,encoder will establish a palette which refers to a table consisting of the dominant color values and use the index of the table to represent each pixel.This dissertation proposed parallel fast schemes for palette generation and index mapping processes in the palette mode according to the single instruction multiple(SIMD)structure of GPU.The cooperation between CPU and GPU can increase the encoding speed of real-time video encoder.