1. A colour image enhancement method, for enhancing the colour of a colour image comprising a plurality of pixels, the method comprising: mapping a colour saturation value of each pixel to a normalised saturation value, wherein the range of values of normalised saturation is the same independent of the luminance value of the pixel; estimating a probability distribution of the normalised saturation values; defining a transfer function for modifying the normalised saturation values, based on the estimated probability distribution; and applying the transfer function to the normalised saturation values to generate modified values.