Adaptive bilateral filter for improved in-loop filtering in the emerging high efficiency video coding standard

To face the still growing video compression needs, ITU and MPEG have jointly started a standardization project called High Efficiency Video Coding (HEVC) which aims to improve the compression efficiency of the state-of-the-art H.264/AVC standard for high and ultra high definition video. The HEVC codec still relies on the usual motion compensated, predictive, block based transform coding architecture with block sizes higher than 8×8 being now considered. Furthermore, the codec is also equipped with a Wiener in-loop filter which, together with the H.264/AVC deblocking filter, further reduces the distortion between the original and decoded frames introduced by lossy coding. While this filter allows indeed reducing the sum of square differences between the original and reconstructed frames, it is not specifically designed to reduce the ringing artifacts resulting from the use of large transform block sizes. In this context, this paper proposes to combine an adaptive bilateral filter together with the HEVC Wiener filter. The proposed combined filter allows an average bitrate reduction of about 7% regarding the HEVC codec without the Wiener filter and a 1.5% reduction regarding the HEVC codec with only the Wiener filter, always for the same quality. Moreover, the combined filter also reduces the ringing artifacts according to an objective metric specifically designed to quantify this type of coding artifact.