How colour optical illusions work
Colour illusions are images where the object’s surrounding colours trick the eye into thinking it's a different colour.
The reason for this optical illusion comes down to how humans have evolved to view colour in daylight.
We see the objects around us because light bounces off them and back onto our retinas. When we look at an object, light enters the eye at different wavelengths corresponding to the different colours. This light hits the retina in the back of the eye where pigments pass signals to the brain which in-turn processes these signals as an image. The brain then works out what colour light is bouncing off the object your eyes are looking at by subtracting that colour from the actual colour of the object.
In the examples below, the light is influencing the colour of the surface it’s landing on and, as a result, the brain tries to ignore it.
Examples
1. The Checker Shadow Illusion
The checker shadow illusion is an optical illusion published by Edward H. Adelson, Professor of Vision Science at MIT in 1995. The image depicts a checkerboard with light and dark squares. The optical illusion is that the area of the image labeled A appears to be a darker color than the area of the image labeled B on the 2D plane of the rendered 3D projection. However, they are actually exactly the same color on the 2D plane of the image file (but not necessarily in the 3D projection) which becomes especially obvious if the projected 3D scenery is rendered partially or entirely defective. (Wikipedia)
The checker shadow illusion is an optical illusion published by Edward H. Adelson, Professor of Vision Science at MIT in 1995. The image depicts a checkerboard with light and dark squares. The optical illusion is that the area of the image labeled A appears to be a darker color than the area of the image labeled B on the 2D plane of the rendered 3D projection. However, they are actually exactly the same color on the 2D plane of the image file (but not necessarily in the 3D projection) which becomes especially obvious if the projected 3D scenery is rendered partially or entirely defective. (Wikipedia)
2. The Koffka Ring and Adelson's Koffka Ring
In the following example of Professor Adelson's modulation of the Koffka ring, there appears to be four different colours, however, if you take a closer look, there are actually only three.
Copyright Akiyoshi Kitaoka
3. Simultaneous Contrast
Simultaneous contrast, as identified by Michel Eugène Chevreul, refers to the manner in which the colours of two different objects affect each other. This effect is more noticeable when shared between objects of complementary colours.
In the above image, although appearing to be slightly different, the two inner rectangles are exactly the same shade of grey! This is due to the background provided by the outer rectangles influencing how the inner rectangles are perceived.
More Examples
In the above image, A, B and C are the same colour. Image source: brainden.com
In the above image, A, and B are the same colour. Image source: brainden.com
