A method of converting a three-or-more-color-component image input signal to an image output signal includes acquiring an input signal having a plurality of pixel signals, each pixel signal having three, or more, color components; determining a residual difference for each color component of each pixel signal; determining a limit value of the residual differences; calculating a common scale factor for each of the color components based upon the limit value; and applying the common scale factor to the image input signal to produce the image output signal.