Red-Green 3D glasses are festive, right?

I'm currently in the depths of revising for an exam, trying to get some grading done, and dreaming about baking cookies shaped like Christmas trees instead of doing any of this nonsense. Today's revision project is a chapter on 3D vision - like Avatar or the red-green glasses that used to come in cereal boxes and were way cheaper than going to see Avatar.

My textbook came with red-green glasses, which is awesome.
It was more expensive than seeing Avatar, though.

One of the things I learned along with how 3D vision works, is how to make pictures that look 3D. And so, I present to the world my very-own home-made 3D work of art. red-green glasses required.

And people still think a PhD in Psychology is impractical.

So how does viewing that picture with 3D glasses make your brain think there's a hole in your monitor? And why doesn't it work if you have lazy eye?

Fact #1: Unless you have lazy eye, by virtue of having two eyes, your brain always gets two very slightly different pictures of whatever it is you're looking at. One from your left eye, and one from your right eye. If you do have lazy eye, your brain ignores one of these pictures in favour of the other one.

Fact #2: There is a systematic relationship between the differences in the two pictures and how far (in depth) something is from the thing you're looking at. 

Here's what's really cool - the brain can exploit these relationships at high speeds to give us this extremely vivid perception of depth. Usually, we don't think photos are 'missing' anything, but the difference between a perceived depth and a projection of a 3D scene on to a flat surface is really amazing once you see a 3D photo. 

There are a ton of beautiful stereo-photos of old japan, taken by Japanese photographer Enami, collected on Flickr by Okinawa Soba. 

From Okinawa Soba's set

If you make them into animated images, the depth appears.

I used photoshop to make this one

Again, from Okinawa Soba

into a 3D image that works with red-green glasses: 

Fun! Unfortunately, I don't think photoshopping 3D images is going to come up on the exam.