1. A colour image enhancement method, for enhancing a colour of a colour image comprising a plurality of pixels, the method comprising: (a) mapping a colour saturation value of each pixel to a normalised saturation value, wherein a range of values of normalised saturation is the same independent of the luminance value of the each pixel, wherein the colour saturation value of the each pixel is represented relative to a maximum saturation value dependent on at least one of the luminance and the hue of the each pixel; (b) estimating a probability distribution of the normalised saturation values; (c) defining a transfer function for modifying the normalised saturation values, based on the estimated probability distribution; (d) limiting local gain of the transfer function to a predetermined value; and (e) applying the transfer function to the normalised saturation values to generate modified saturation values, wherein the colour image includes a plurality of luminance regions and method steps (a) to (e) are performed on the colour image irrespective of different luminance values in each of the plurality of luminance regions thereby computing only one histogram for the plurality of luminance regions.