Video coding with pixel-aligned directional adaptive interpolation filters

In this paper a novel adaptive interpolation filter structure is proposed to improve the coding efficiency of video coders. Proposed scheme utilizes one dimensional directional adaptive filter for every of the sub-pixel location, whose coefficients are calculated analytically for every frame by minimizing the prediction error energy. The direction of the interpolation filter is different for every sub-pixel position and it is determined based on the alignment of the corresponding sub- pixel with integer pixel samples. Experimental results show that, the proposed method achieves up-to 1.1 dB gain compared to the standard non-adaptive interpolation scheme of H.264/AVC, requiring less number of operations for interpolation. Compared to two-dimensional non-separable adaptive interpolation, proposed scheme has practically the same coding efficiency with approximately 3 times less complexity. Since significant coding efficiency is achieved without increasing the complexity, it is believed that proposed method has important use-cases in mobile multimedia environments where the resources are severely constrained.