by John Walker 25th April 1996 Most computer applications specify colour in three-component systems such as RGB, HLS, or HSV. Derived from the mechanisms of human colour perception, these colour spaces map relatively straightforwardly onto display and printing technologies. While human colour perception is well modeled by such systems, the physical interaction of light and matter is far more complicated. To correctly display the effects of dispersion in refractive media, diffraction, or absorption by nontrivial filters, image synthesis tools must consider the spectrum of the electromagnetic radiation and the spectral dependence of its absorption, reflection, and other interactions with objects; perceptual abstractions such as RGB are inadequate. A task as simple as rendering a scene under a variety of light sources: daylight, incandescent and fluorescent indoor lighting, an...