Adaptive Interpolation Filter for Motion and . . .

Common motion compensated hybrid video coding standards such as H.263, MPEG-1, MPEG-2, MPEG-4 are based on a fractional-pel displacement vector (DV) resolution of 1/2-pel. Recent approaches like MPEG-4 (ACE-profile) and H.26L use higher DV resolutions of 1/4-pel and 1/8-pel. In order to estimate and compensate fractional-pel displacements, the image signal has to be interpolated. Especially for higher DV resolutions an efficient interpolation filter is necessary [13]. Thus, in MPEG-4 (ACE-profile) and H.26L 6 or 8-tap Wiener interpolation filters are applied [5,3]. These Wiener filters were designed to interpolate the image signal while reducing spacial aliasing components that deteriorate the motion compensated prediction [6]. In [12] we presented an improved interpolation filter that allows to interpolate an aliasing affected image more accurate then the conventional Wiener filter. This filter is a combination of the Wiener filter and a motion compensated interpolation filter. Up to now these filters are based on invariant filter coefficients. The same coefficients are applied for all sequences and for all images of a sequence. In [10] we presented an adaptive interpolation filter that improves the coding efficiency by reducing the impact of displacement estimation errors and by compensating the aliasing components. The interpolation scheme of [10] is based on filter coefficients that are adapted once per frame to the non-stationary statistical features of the sequence. This paper introduces a motion compensated adaptive interpolation filter that combines the frame-adaptive approach of [10] and the motion compensated interpolation approach of [12]. Due to the motion compensated adaptive interpolation filter, the coding efficiency of an H.26L codec is improved up to 0.8 dB.