Illusion Comes to Life: the Science of 3D

How does our brain make us see a rose pop out of this flat splotch of red paint?
 

It starts out as an oblong red blob. The outer lines of the blog converge in the distance, so my eyes tell my brain that it's about 25 feet back-to-front.

As the artists adds black shading to the red splotch and petals start to pop out, suddenly it's a round red rose. The shadows tricks my brain into thinking I'm seeing a different object all together. Suddenly, what was the back of our blob, is the top of the rose, and my brain uses the sides of the rose instead of the back of the blob to determine how far back the object goes into space.

The human eye calculates distance by by how much each eye tilts to see something. Since the eyes are set apart, looking at a farther object means less inward eye tilt, closer means more inward eye tilt. Look at your nose, and the acuteness of you inward eye tilt makes you look cross-eyed.

In the final concrete painting, we register the sides of the rose with our eyes and our brain tells us it's close, not far. The effect of the shadow on our brain's perception of 3D is tremendous, as Rembrandt or Cezanne knew well. The artist here take full advantage of it.

So, that's how the rose seems so close. But, how do I see 3D in the first place? Simple. Camera 1, camera 2. My eyes see in stereo which means they spot slightly different images at the same time from their slightly different vantage points. The slightly different images combine into one image in the brain, an image which basically presents almost two sides of a thing and registers it as 3D:

Again, the shadows on the flat painting do the work of telling our brain that our eyes are viewing a 3D object from different angles. Cool trick. But not new...

Rembrandt self portrait, round face accomplished through shading.