Opponent process is a color theory that states that the human visual system interprets information about color by processing signals from cones and rods in an antagonistic manner (source).
What is the advantage of opponent color against RGB color? For example, in object recognition or edge detection?
Can we say that it provides some level of invariance to changes in brightness?
Answer
RGB color is a more direct representation of the "raw input" received by the (human) eye, since the three types of cone cell have responsivity spectra that roughly correspond to red, green, and blue light:
Opponent color decomposes color into three "dimensions" of opposing properties: dark or light, yellow or blue, and red or green. This provides some brightness invariance, since changing the intensity of light will change the brightness but not the yellow/blue or red/green balance of the color, even though the stimulation level of all three types of cone cell will change.
One could speculate that opponent color perception is more "meaningful" in real-world environments. The dark/light axis represents the overall amount of light, the yellow/blue axis indicates which end of the visible spectrum is predominant, and the red/green axis provides a finer distinction for low-frequency light.
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