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; applying an appropriate perceptual-based color difference model to said determined location of each color within said device-independent color space to generate two color differences for each color, wherein each color location within said device-independent color space is expressed in a first and second Euclidean distances, and each color difference is based on said first Euclidean distance and said second Euclidean distance, wherein said appropriate perceptual-based color difference model is separately applied on said first Euclidean distance and said second Euclidean distance, wherein CIEdE2000 is applied to colors having an Euclidean distance less than 20, and CIELab is applied to colors having an Euclidean distance greater than 20 but less than 30; normalizing said two color differences for each color under a predetermined range; mapping said normalized color differences to an output range of an output device; and outputting a grayscale representation of said color image on said output device by using said normalized color differences.