In a previous post we looked at how to produce the contrast illusion shown above. Simply stated the letters on the right appear lighter than those on the left. They are the same colour. The effect results from the graded background. This possibly results from the electrophysiological properties of the Retinal Ganglion cells. What happens if we change the colours in the background or in the letters themselves? Here are some examples.
What is interesting about this black text on grey background is that the illusion vanishes. All other colours will be lighter and perhaps the original effect relies on background colours being both lighter and darker than the letter colours.
In the same vein, the effect also appears to be lost here.
The blue on grey combination produces a contrast effect. In the word ‘contrast’ the first few letters appeared to me to be darker than the last few although I will leave it to the reader to see if they are persuaded. Perhaps the effect is stronger if the background and letter colours are similar.
The effect seems more marked here than in the previous diagram. Perhaps then the contrast illusion depends on a contrasting background and letters of similar colour.
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