1. A method of detecting skin tone pixels in an input image and adjusting colour values thereof for an output image, the method comprising: determining, by software running on computer equipment or software embedded in an integrated circuit or dedicated hardware, for each of a plurality of pixels in an input image whether initial chromaticity values of each of said pixels lie within a skin tone area defined in a chromaticity plane; and, amending, by the software running on computer equipment or the software embedded in an integrated circuit or the dedicated hardware, the initial chromaticity values of those pixels that have chromaticity values lying within said skin tone area to obtain amended chromaticity values for use in obtaining an output image, wherein, for each of those pixels that have initial chromaticity values lying within said skin tone area, the chromaticity values are amended by an amount that depends on a distance of said initial chromaticity values for said pixel from a point within the skin tone area.