Optimization HEVC Intra Prediction Algorithm

The High Efficiency Video Coding (HEVC) standard was developed by JCT-VC in2010and was officially released in2013.Compared to the previous video coding standard of H.264/AVC, HEVC can save about50%bit-rate for equal perceptual video quality, but the computational complexity significantly increases. Therefore current research is focusing on decreasing the computational complexity and improving the coding timeliness of the HEVC video coding algorithm. In view of this, this thesis mainly studies on optimizing the intra coding algorithm. The main achievements are as follows:1) For the high computational complexity caused by too many times splitting of coding blocks in LCU (Largest Coding Unit), this thesis proposes an early CU splitting algorithm. Firstly, the algorithm makes use of image’s texture features to analysis the correlation between neighboring coded blocks under different depths, and then proposes a splitting scheme of coding blocks under different depths. The scheme determines whether the lower right coding block needs to be split by using the splitting information of the left, above and upper left coded blocks. Experimental results show that:Compared to the original algorithm, the proposed algorithm saves about17.79%coding time while the bit-rate increases about1.02%, and PSNR decreases about0.045dB.2) Base on studying the algorithm of mode decision in intra prediction, this thesis proposes a fast intra prediction mode decision algorithm. Firstly, this thesis divides RMD (Rough Mode Decision) process into two steps namely early selection and later selection, thus the number of modes for RMD is reduced; then formulates a scheme that can select the optimal prediction mode in advance by exploiting the relationship of the first mode in candidate list and MPM (Most Probable Mode); Finally, the modes in candidate list are grouped, thus modes that are used for computing the rate-distortion cost are adaptively reduced. Experimental results show that:compared to the original algorithm in HEVC, the proposed algorithm saves about25.1%coding time while the bit-rate increases about0.04%, and PSNR decreases about0.034dB.At last, this thesis combines the two above algorithms into one algorithm. Compared to the original algorithm in HEVC, the new algorithm can save about37.16%coding time with the bit-rate increases about1.08%and PSNR decreases about0.075dB on average.