1. An image processing method for de-mosaicing 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 mosaic, the method comprising the steps of: i) generating from the image mosaic a high spatial frequency luminance image that extends across all pixel locations of the image mosaic, each pixel having a luminance value; ii) adjusting the luminance values of pixels in the high spatial frequency luminance image in order to reduce mosaic artefacts, said adjustment being performed on pixels generated from a particular colour value at least in a first row and/or a first column of the high frequency luminance image according to the luminance values for said pixels and the luminance values of pixels generated from another colour value; iii) generating for each colour value from the image mosaic a low spatial frequency luminance image, each pixel having a luminance value; and iv) after the adjustment of step ii), combining across all pixel locations the high frequency luminance pixels with each of the low frequency luminance images in order to generate a de-mosaiced image for each of the colour values corresponding to said low frequency luminance images.