Interpolation filter design in HEVC and its coding efficiency - complexity analysis

Coding efficiency gains in the High Efficiency Video Coding (H.265/HEVC) standard are achieved by improving many aspects of the traditional hybrid coding framework. Motion compensated prediction, and in particular the interpolation filter, is one of the areas that was improved significantly over H.264/AVC. This paper presents the details of the motion compensation interpolation filter design of the H.265/HEVC standard and its improvements over the interpolation filter design of H.264/AVC. These improvements include discrete cosine transform based filter coefficient design, utilizing longer filter taps for luma and chroma interpolation and using higher precision operations in the intermediate computations. The computational complexity of HEVC interpolation filter is also analyzed both from theoretical and practical perspectives. Experimental results show that a 4.5% average bitrate reduction for the luma component and 13.0% average bitrate reduction for the chroma components are achieved compared to interpolation filter of H.264/AVC. The coding efficiency gains are significant for some video sequences and can reach up to 21.7%.