How 3D Glasses Work

The idea of breaking an image up into its components so that the brain perceives it as three-dimensional is not a new one, as evidenced by the fact that Batman comics have been featuring various types of such goggles for close to five decades. Still, most people don't know how they work, or why images seem to come out of the movie theater screen. Here are a few basic tips to understanding how 3D, or stereoscopic images are formed.

First of all, you have to always remember that two cameras are used at all times while filming seemingly 3D scenes. The trick is to shoot the same thing from two slightly different angles, which reproduce the 2-inch (5-centimeter) distance between the human eyes. Naturally, we are born to see stereoscopically, but our brain merges the two slightly different images from our eyes together, and allows us to see objects in 3D as “default.”

In the case of 3D movies, for example, producers have to film the same scene using two cameras, set slightly apart. These capture the images that are then superimposed on each other. But the trick is the light filter used for each of the cameras, and this is the second most important detail. One of them has to shoot using a reddish filter, while the other needs to use a cyan, green or blue one. Once people arrive in the cinema, they are given a pair of glasses, which have carefully-designed lenses.

Each of the lenses has a a certain color, but one is always red, while the other can have any of the remaining three. The light filters mean that images that have been shot by the first camera, using a red filter, will only enter the right eye, while footage from the second camera, which has been shot in green, only enters the left one. This color-coding is essential in helping the brain put the pictures back together.

If, when watching a 3D movie, you take your glasses off during intense scenes, you will see that what appears on the screen may not seem like a good film, in that the image is completely out-of-focus. Without the goggles to code and control each picture on it, your brain perceives the movie exactly how it appears – an undecipherable combination of images and colors that make no sense.