How does 3D TV Work?

by Jack Burden

A television screen can only display 2D images so how does a 2D image become 3D? 3D TV works because as a human being you have stereoscopic vision. This means that you have 2 eyes with space in between them; that space, however small, forces you to see objects from 2 slightly different angles. When your brain combines these images it gives you the ability to judge depth and therefore the distance to an object. On average this distance can be judged very accurately out to about 25 feet (8 meters), further away and the angles your eyes are viewing the object at are too narrow to accurately judge depth. At that point you are relying on the relative size of an object of known size to judge how far away it is and not just your eyes.

So how does 3D TV take advantage of our Biology to create the illusion of 3 dimensions? It shows a different picture to each of our eyes, both pictures are of the same thing at slightly differing angles and this forces our brain to give the 2D image apparent depth.

There are a few different ways that this can be accomplished. The most common way is by using a set of glasses that only allows one of the dual images through to each eye. Most everyone has seen the paper 3D glasses that have two colored cellophane lenses, for these to work both images are shown at the same time on the screen and each uses a different color to separate it. The colored lenses filter out one of the images and you get a separate image to each eye and the illusion of depth is created. At first this method would only work with monochrome images but advancements have allowed full color images to be shown using this method, called Anaglyph 3D. Using color filters still mutes the color of the picture an is no longer the preferred method of showing 3D.

Polarized glasses look like regular sunglasses. The lenses are polarized to only allow certain wavelengths of light through and like Anaglyph 3D both images are combined into one frame and shown to the viewer. The two images use different light wavelengths and the polarized lenses filter out one image or the other showing the separate pictures to each eye. This again creates the illusion of depth and provides the 3D effect. This is the method used in 3D movie theaters and in some of the new passive 3D TVs introduced in 2011.

The third method involving glasses is called Active 3D. In active 3D the glasses you wear are actually two LCD screens, using a sync signal broadcast by the TV the lenses alternate open and closed. The television shows the images in sequence instead of them being combined into one image. The television alternates the images very quickly, left eye image, right eye image, left eye image, right eye image and so on. The sync signal tells the LCD glasses to open and close in time with the images shown and you again get the impression of depth. This method provides the "deepest" 3D images but in doing so effectively halve the frame rate of the content. Most modern TVs are capable of doubling the frame rate so this isn't really a problem anymore. Some viewers can find this method of 3D uncomfortable to view and can get headaches or nausea during extended viewing.

The final method of 3D display, the holy grail of 3D TV, is "glasses free" 3D. This method uses a controllable filter on the screen and a camera with facial recognition technology to only show the correct image to each eye. Both images are broadcast at the same time and the filter creates angles to only show the correct image to each eye. The camera and facial recognition software keeps track of where your eyes are and the filter adjusts to follow your position to keep showing you 3D even if your head moves. Sony and Toshiba both showed glasses free TVs at the 2011 Consumer Electronics Show but these models were just prototypes and will not be available for sale any time soon. Although this technology is still in it's infancy you will be able to experience it with Nintendo's 3DS handheld game system soon.