1. An image processing method for correcting colour aliasing artefacts in an image mosaic, the image mosaic being composed of a plurality of image pixels and each image pixel having one of at least three colour values and having a luminance value representing the intensity of the colour value for that pixel in the image mosaic, the pixels of each colour value being interleaved in rows and columns across the image mosaic with pixels of different colour values to form the image, the method comprising the steps of: i) for one or more of the colour values, assessing at locations in the image mosaic an edge strength metric using at least two luminance values of the same colour value at locations in the image mosaic, the edge strength metric being indicative of the strength of luminance changes across said locations, and hence of detected edges at said locations; and ii) generating for each colour value a corresponding low spatial frequency image in which changes in luminance values are smoothed, said smoothing for each colour value being in accordance with said edge strength metric so that smoothing at the locations of detected edges is inhibited.