  A symmetrical model of color vision, the decoding model as a new version of
zone model, was introduced. The model adopts new continuous-valued logic and
works in a way very similar to the way a 3-8 decoder in a numerical circuit
works. By the decoding model, Young and Helmholtz's tri-pigment theory and
Hering's opponent theory are unified more naturally; opponent process, color
evolution, and color blindness are illustrated more concisely. According to the
decoding model, we can obtain a transform from RGB system to HSV system, which
is formally identical to the popular transform for computer graphics provided
by Smith (1978). Advantages, problems, and physiological tests of the decoding
model are also discussed.
