The opponent process is a color theory that can be explained as follows:

Athough the human visual system at its frontend (eye) detects color with three types of cones (trichromatic theory), this is not the way color is processed further on by the human visual system. The human visual system processes these primary input into an opposing color system.

The opponent color theory was first proposed by Ewald Hering in 1872 (Hering E., 1964). The opponent color theory suggests that there are three opponent channels: red versus green, blue versus yellow, and black versus white (luminance), with each responding in an antagonist way. That is, either red or green is perceived and never greenish-red. (Note that although yellow is a mixture of red and green in the RGB color theory, the eye doesn't perceive it as such.) In 1957 Hurvich and Jameson provided quantitative data for the color opponency theory of Hering (Hurvich LM, et al, 1957).

The opponent color theory can be applied to computer vision and implemented as the Gaussian color model (Geusebroek J. M. et al 2001).

References

• Geusebroek J. M., van den Boomgaard R., Smeulders A. W. M.,Geerts H., Color invariance, IEEE Trans. Pattern Anal. Machine Intell., 2001; 23(12):1338-1350.
• Hering E., Outlines of a Theory of the Light Sense, Cambridge, Mass., Harvard Univ. Press, 1964.
• Hurvich LM, Jameson D, An opponent-process theory of color vision, Psychol Rev 1957; 64:384-404.