Study On Fast Algorithm Concerning Inter PU Mode Decision For HEVC

The newest generation of video coding standard-HEVC can save half bit rate compared to H.264/AVC standard and achieve the same coding quality.However,the coding complexity is greatly increased.While the coding framework of HEVC is determined,fast algorithms aiming at saving time of its coding process become the important ways for the promotion and practical value of HEVC.This thesis has conducted studies to the inter PU mode selection,and proposed three fast algorithms for inter PU mode selection.The main work and contributions are as follows.(1)The optimized PU mode selection algorithm based on fuzzy logic is proposed.In this algorithm,texture and gradient are used to judge the reference value of spatial and temporal adjacent coding units for the current coding unit.According to the idea of fuzzy logic,coding units are divided into direct acceleration type,loose acceleration type and non-acceleration type.For coding units that in the direct acceleration interval,the best modes in the same depth of the reference coding units are used for direct acceleration.For those in the loose direct acceleration interval,an optimization algorithm that uses PU mode reference list based on spatial location is advised.And no change is done to the coding units in the non-acceleration interval.Morever,to improve the performance of the proposed algorithm in all kinds of video and video clips,dynamic thread control technology is included.Experiments show that in Low Delay configuration,the bit rate increases by 0.7%-2.2%,the PSNR decreases by 0.01-0.05 dB,and 60%-75% time saving is achieved,compared to the standard test model HM 16.0.(2)The optimized PU mode selection algorithm based on acceleration tolerance is proposed.The above algorithm uses speed-up ratio,which is the acceleration conditions of the previous coded units,to adjust the dynamic threads.To a certain extent,it improves the algorithm.However,there is still certain “hysteresis”.Based on experimental data,some conclusions about the relationship between video characteristics and acceleration characteristic are obtained,and two mathematical model formulas based on speed-up tolerance are proposed.Before the PU mode selection procedure,analyse the characteristics of the current coding unit and adjust the threads.In this way,the acceleration strategy is better selected.Experimental results show that in Low Delay configuration,the bit rate increases by 0.2%-1.6%,the PSNR decreases by 0.01-0.04 dB,and 60%-72% time saving is achieved,compared to the standard test model HM 16.0.(3)The optimization algorithm for PU mode selection procedure in non-I scene switch frames is proposed.Before mode selection,this algorithm can accurately classify whether the frame is scene switch frame or not by the Hash Index-based video motion intensity detection.For scene switch frames,this algorithm set the current frame as I frame and conduct intra coding directly.Experiment results show that in Low Delay configuration,the bit rate and PSNR are not changed and the proposed algorithm achieves 42%-53% time saving of the scene switch frame coding.Meanwhile,it achieves about 5%-10% time saving of the whole video coding,compared to the standard test model HM 16.0.Finally,summarize the work in the study and describes possible directions for future work.