The present invention relates to a method for determining filter coefficients of a separable two-dimensional adaptive interpolation filter used for motion compensation with sub-pel resolution, a corresponding method for video data compression with adaptive filtering, and a corresponding apparatus. According to the present invention, the two-dimensional interpolation filter is separated into a one-dimensional horizontal interpolation filter and a one-dimensional vertical interpolation filter. Filter coefficients of the first one-dimensional interpolation filter are determined from blocks of video data having motion vectors that indicate a full-pel displacement in the interpolation direction of the second one-dimensional filter. The first one-dimensional filter may then be applied to the video image so as to obtain one-dimensionally interpolated blocks of video data. Filter coefficients of the second one-dimensional interpolation filter are then determined in a second step from interpolated blocks of video data having motion vectors that indicate a sub-pel displacement in the interpolation direction of the second one-dimensional filter. According to this invention, filter coefficients can be determined in a highly efficient manner by solving systems of linear equations.
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