How we see 3D

Dr Adrian Dorrington, a scientist from the University of Waikato, explains how the brain interprets the images our two eyes receive. The net result is that we experience depth perception. 3D television works in a similar way. By wearing special glasses, two pictures are shown at the same time, one to each eye. The brain interprets this such that we see in 3D.

Transcript

DR ADRIAN DORRINGTON
Humans perceive depth because we have two eyes. For example, if you were to hold out a finger and close one eye and then swap to the other eye, you’ll see that your finger appears to move relative to the background. So because our brains see this difference, then we can estimate how far away things are.

So we see stereoscopically, that is we see two different images, and then the brain takes those images and it finds the differences between the images it sees and the discrepancy between those images, and the larger the discrepancy, the closer an object is, so an object further away doesn’t appear to change between the two eyes.

So 3D TV works by showing two pictures at the same time, but each picture is delivered to the individual eyes. One eye we see one picture, the other eye we see another picture, so it’s really tricking the brain into seeing a three-dimensional image.

There’s several different ways of delivering those two different images to the two different eyes. One of the older ways is with those red-blue glasses called anaglyph, and you put the glasses on and you look at a picture, and part of the picture is in red and one eye will see that, and part of the picture is in blue and another eye will see that. By splitting the picture into the two different colours and wearing the two different coloured glasses, you can have the two different images coming to the different eyes.

Another technique for delivering the different images to the different eyes is to use polarisation in the glasses, so you put the glasses on and one side is polarised horizontally and one side is polarised vertically, and the two images that are presented are also polarised, so the polarised filters mean that the horizontally polarised image is delivered to one eye and the vertically polarised image is delivered to the other eye.