Our visual system can interpret colors and shades in surprising ways. With this 3×3 Tic-Tac-Toe grid I would like to show that our sensibility to color brightness can be easily fooled. Well, do you notice something particular in the grid below?
In fact, the large green square behind the grid hasn’t a uniform color as it looks,
but is checkered with dark and light green boxes.
Our visual system works like a “comparative computer”. In fact, we never see colors in isolation, as the appearance of any color is affected by the colors surrounding it. So, under certain conditions, colors that are identical may appear different, while colors that are different may look the same. In our visual system there is a mechanism that enhances the contrast of the outline of an object relative to its background: it is called “lateral inhibition”.
Thus, even small differences in brightness between adjacent zones, or objects, are deliberately increased by our visual system and the brain to better distinguish them. But something strange happens when the brightness boundaries of the color zones are concealed: the cues the brain needs to trigger the lateral inhibition no longer exist and consequently we become blind to variations in color brightness, as shown in the animated gif.
