Wednesday, June 21, 2023

Ponzo Illusion

The Ponzo Illusion demonstrates the principle that our minds estimate the size of an object based on surrounding background cues.


The illusion was first described by Italian psychologist Mario Ponzo in 1913. In its simplest form, the illustration shows two lines of equal length are placed at an angle between two diagonal lines.

The line placed on the top appears to be longer than the one on the bottom. This is because the brain interprets the diagonal lines as converging in perspective, and therefore the upper line must be longer. But of course the segments are really exactly the same size.


The illusion is more compelling when the background cues are more realistic. In this case, all three cars are exactly the same size.

More examples

Wikipedia on Ponzo Illusion

3 comments:

  1. The optical illusion of the cars on a street in perspective had me fooled. I had to but the image in Photoshop and measure the first and last cars. It is amazing!

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  2. I've often thought about incorporating clever optical illusions within art, even on a subtle level. I'm having trouble with the car ponzo illusion -- if I mask off the rest of the picture, the car in the distance seems to be bigger -- what am I missing?

    James, have you ever used these principles in your art work.

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