1. An image processing method for correcting the colour of a colour image, the colour image being composed of at least two sets of image pixels, each set having a distinct colour value, and each pixel having a luminance value representing the intensity of the colour value for that pixel in the colour image, the method comprising the steps of: i) for each colour value, generating from the pixels for that colour value a low spatial frequency monochrome image composed of a set of smoothed image pixels; ii) for at least one colour value, selecting a sub-set of the smoothed image pixels; iii) applying a colour correction function to the or each sub-set of smoothed image pixels in order to generate one or more corresponding sub-sets of corrected smoothed image pixels, said function including for each colour value a contribution from corresponding smoothed image pixels in one or more of the other sets of smoothed image pixels; iv) completing one or more sets of corrected smoothed image pixels by interpolating and/or extrapolating from the or each of the corrected smoothed image pixels to generate similarly corrected smoothed image pixels not in the original sub-set of smoothed image pixels; and v) using the or each set of corrected smoothed image pixels to generate a corrected colour image.