I. Introduction
Video compression becomes more important as resolution of video increases rapidly even in mobile display devices. High efficiency video coding (HEVC) or H.265, one of the latest video compression standards, was ratified in April 2013 [1] while aiming at two times higher coding efficiency than the former standard, H.264/AVC [2]. In addition to many other improvements, the HEVC introduced a new coding tool: sample adaptive offset (SAO), which works as another in-loop filter at the right next stage of the deblocking filter.