Color images can be displayed in many different kinds of devices: CRT monitors [160], liquid-crystal displays (LCDs) [491], plasma display panels (PDPs), field-emission displays (FEDs) [451], organic light-emitting diodes (OLEDs) [865], and other eletroluminescent displays (ELDs) that receive electronic signals and produce color images on the display screen. The images are transient in the sense that they last not much longer than the electric signals. They are called soft-copies. In comparison, color images that are printed on reversal films (slides) and papers, by photographic processes, inject printing, thermal dye transfer, and offset printing, last much longer after the printing is completed. These are called hardcopies.

Color images displayed as soft-copies are almost exclusively based on additive color reproduction, in which colors are produced by additive mixtures of three or more primary colored lights (usually red, green, and blue). In comparison, color images produced by hard-copy devices mostly use subtractive color reproduction, in which part of the light spectrum is selectively removed from the illumination on the hard-copy. For example, cyan ink removes mainly the long-wavelength part of the illuminant spectrum. The more cyan ink is deposited on a paper, the less “red” light is reflected from the print. Different colors are produced by controlling the amounts of cyan ink, magenta ink, yellow ink, and black ink (to produce very dark colors).

Therefore, there are two major topics in our study of color image displays. The first is the device or the medium itself, and the second is the method of color reproduction for that display.