Fast CU Size and Intra Mode Decision Algorithm in HEVC Standard

With the expansion of the Internet and wireless technologies, video-related applications have been expanded much more than ever. But since network bandwidth is limited, better high-gain video compression methods remain essential. Recently, the new video compression standard called "High Efficiency Video Coding" (HEVC) has been introduced, which doubles the compression compared to the previous standard called "Advanced Video Coding", while preserving video quality at the same time. In HEVC standard, 35 intra prediction modes have been defined to improve the efficiency of encoding algorithm. The best intra prediction mode is chosen using a process called "Rate Distortion Optimization". The purpose of this study is to propose a method to reduce the number of intra prediction modes in RDO process, since it is a very time consuming process. A new method based on Sobel operator is proposed for fast determination of intra prediction mode as well as coding unit size in HEVC. Although Sobel operator is an essential part of our algorithm, other features were extracted from coding control part of HEVC algorithm to excel the speed of coding process, since the main purpose of fast coding algorithm should be to reduce complexity while producing a bitstream, which preserves the quality of decoded video. These features are parent CU mode, modes with lower cost functions and modes that are determined to be most probable via pervious researches. Parent CU mode is intra angle of coding unit that contains the current CU and is available at the time of calculating the best mode for current CU. Modes with lower cost functions are modes that have the least cost function value that are calculated by HM via a fast algorithm and modes that are determined to be most probable via pervious researches are DC and horizontal and vertical modes. Coding time compared to HEVC reference software (HM) using the proposed fast method is reduced by an average of 56% and by using the proposed precise method is reduced by an average of 29%. In proposed precise method, final video quality degradation is negligible.