Pushing the (parallax) barrier: 3D Technology

Before we take a look at the impact of stereoscopic displays on the visual system it is important for us to look at the differing designs currently on the market. The most prominent two systems can be classified as with glasses and without glasses. Today we will discuss the options for without glasses.
Glasses free stereoscopic displays are also called auto-stereoscopic, unsurprisingly as the stereo-effect happens automatically. Currently only parralax barrier technology has made it mainstream although other technologies are slowly progressing, such as lenticular arrays.

Parallax barrier technology works by physically separating the images being projected by a source, typically a screen, much like how the Turville balance uses a septum. The technique is generally accredited to Frederic Ives who is said to have discovered it sometime between 1901 and 1903 (he also co-coincidently invented colour photography way back in 1885). Whilst Ives' technique was not re-used until the 21st Century a modification of it, called lenticular parallax was and you might be more familiar with it than you think; all the rulers which have images that seem to move when you wiggle the ruler use this effect.

Bringing back childhood memories: Lenticular Rulers

In the modern day whilst technology may be more sophisticated the principals of parallax barrier technology is not. There are two current variations of the pixel barrier in present use. The first is a series of slits placed in-front of the LCD screen, this has the advantage of being very cheap but it does reduce image intensity and viewing angle. A second technique has been devised to overcome this limitation which is to insert a barrier behind the screen but in-front of the illumination. This means that whilst the image being projected is identical for each eye, the lighting is not and the alternate pixel image is bleached out; thus creating auto-stereoscopy. This lighting method is what is being used in the Nintendo 3DS and some 3D smartphones. Television incorporating it are slowly coming to market with Sony, Toshiba, Sharp and Panasonic all showing off their designs at recent trade shows.

A Parallax Barrier Screen Principle

Lenticular lens displays, are similar to the parallax barrier technique however they use an array of cylinders to create the effect of a parallax barrier. This technique was used in the 1990s to early 2000s but with the advances in parallax barrier technology described above had fallen by the way side somewhat. One interesting device which does use the lenticular array system is the 3DeeSlide, designed to make non-native displays 3D compatible.

A Lenticular Array Screen Principle

A similar technique to lenticular lens displays is Integral imaging displays, these use a multitude of lenses to create an image with perceived depth through optical distortion, this has the benefit of inducing a normal accommodative action for the depth being viewed, but is currently best filed under future-technology with tech firms only really beginning to explore its potential.

The other technique in use presently is eye/head tracking. This is a very clever, though currently limited system in which the position of a users head or eye position is traced by a camera. If you're reading this and have an iPhone (or any iOS device with a front-facing camera) to hand you can see a crude version this technique yourself using i3D. The more refined version uses eye tracking to create a 3D auto-stereoscopic image relative to the viewers position using switchable LCDs. Though this technology is not expected to penetrate the mass-market until a few years time with the advent of holographic displays.