Block Adaptive Interpolation Filter Using Trained Dictionary for Sub-Pixel Motion Compensation

Adaptive interpolation filtering for sub-pel motion compensation is one of key techniques of ITU-T key technology area (KTA) codec. However, the adaptive interpolation filtering has a limitation in coding efficiency because of its frame-based update strategy of filter coefficients. Although switched interpolation filter with offset is presented as a sort of block-adaptive filtering for KTA codec, its coding efficiency is generally lower than that of the best adaptive interpolation filter. In order to overcome such a problem, this paper presents an advanced block-adaptive interpolation filtering using well-trained dictionaries which store optimized filter coefficients. We derive those filter coefficients by using learning-based super-resolution. The proposed block-adaptive interpolation filtering for quarter-pel motion compensation consists of two steps: up-scaling of half-pel accuracy and subsequent up-scaling of quarter-pel accuracy. The dictionary optimized for each step is employed to produce the precise up-scaled pixels. Simulation results show that the proposed algorithm improves higher coding efficiency than the previous adaptive interpolation filters for KTA.