1. A method for converting a color representation of an image to a grayscale representation, said method comprising: determining, for a color image, a location of each color within a device-independent color space; determining a color difference of each color by applying an appropriate perceptual-based color difference model according to its determined location within said device-independent color space; normalizing said determined color differences for each color under a predetermined range; and mapping said normalized color differences to an output range of an output device.