It’s an Illusion, Part 6 – Inside or Out?


Convex or Concave?

There is something interesting about creating two dimensional images of concave and convex surfaces.  They look so similar that we need cues to tell us which of these shapes our eyes are looking at.  A curved surface can look convex in one context, and concave in another.  Are we looking at it from inside, or out?  From above or below?  When there are no clues, or the context is not clearly defined, the brain struggles to decide what it is looking at.

Escher makes good use of this in “Convex Concave”.  It is an image which can be seen in many different ways, and one that seems to change as your eye travels around it.  A pillar marks an outside corner at one glance; turns inward at the next.  Windows and roofs change shape and direction.  The same curve becomes a bridge for walking on or the inside curve of a ceiling.  If you see a shape as convex, the surface beside it looks as if it faces in one direction – if it looks concave, then the surface beside it seems to point a different way.

It’s an elusive illusion.


M. C. Escher, Convex Concave


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