1. A method of pixel interpolation in which a two-dimensional digital filter is arranged so as to interpolate an output pixel from a two-dimensional array of input pixels, the method comprising: detecting the direction of an image feature at a pixel position to be interpolated; applying a shear transformation to the digital filter and/or to the array of input pixels so as to map the operation of the filter to the detected image feature direction in respect of at least a first one of two axes of the two dimensional filter; and applying the digital filter to obtain the output pixels.