On the drawing below, the grey colour of the squares marked as A and B is exactly the same. Still…
It is not often that you find the most simple and lighter illusions described as actively than on the web site for the MIT (Massachussets Institute of Technology).
Lightness Perception and Lightness Illusions
interactive movies based on a paper by Edward H. Adelson
Anamorphosis is a technique to hide images in another image. It has long been used by painters. And some of them are quite well known like the The Ambassadors (Hans Holbein the Younger, 1533) below.
In this painting, there is a highly deformed skull appearing like a whitish blade at the bottom of the painting.
1. Stare at the image for 10 seconds
2. Look at something — your hand, a book, your friend
For more on illusions — and the delight of our buggy minds — see Al Seckel’s 2004 TEDTalk.