Square Optical Illusion

Is the red figure a perfect square?

See Another Random Optical Illusion

Scroll down for the answer and explanation.

Yes.

Explanation

The contrast between the points of the square and the smoothness of the circles makes the angles appear sharper than they actually are in this distortion type optical illusion. We are unaware of a really good explanation why, but believe it is because we are constantly trying to make what we see into a 3D object and we adjust and distort the object if necessary to make the 3D version fit reality.