3D, every few years you’ve probably watched a mainstream movie through a pair of glasses that make creatures, people and explosions pop out of the screen. And if you’ve bought into the massive hype, you were probably queueing up for James Cameron’s Avatar, which was screening in 3D. You might wonder, why can’t more movies be shown in 3D? It would just take some post-production video rendering and a pair of stereoscopic glasses, right?

Actually, 3D projection is a lot more complicated and expensive than one would think. Wired paid a visit to Dolby Laboratories in San Francisco to learn about the history of 3D movie technology leading up to its current state.

Remember those junky glasses, with a blue lens for one eye and a red one for the other? They were tied to a 3D-imaging method called anaglyph that dates back to the 1950s. With this system, the images on the screen were projected with two colour layers superimposed onto one another. When you put on the glasses, each eye sees a separate visual, the red-tinted image through one eye and the blue-tinted one through the other. Your visual cortex combines the views to create the representation of 3D objects.

Though it may have been impressive at the time, early anaglyph imaging suffered from many issues. The colour separation on film was very limited, and thus it was difficult to perceive details in 3D scenes. Another frequent problem was ghosting, which happened when the image that should be appearing in your left eye would creep over to the right.

And then there’s the screen. Cinemas projecting 3D movies with the anaglyph method have to install silver screens for an ideal viewing experience. That’s because the more reflective screen helps keep the two different light signals separated.

3-D movie technology has come a long way. Anaglyph imaging has improved: glasses are now typically red and cyan, which, when combined, can make use of all three primary colours, resulting in more realistic colour perception.

RealD cinema, currently the most widely used 3D film system in cinemas, uses circular polarisation produced by a filter in front of the projector to beam the film onto a silver screen. It does not require two projectors shooting out images in separate colors. The benefit of polarisation is you can move your head without losing perception of the 3D image.

Dolby’s 3-D system, used for some Avatar screenings, is a little different. It makes use of a filter wheel installed inside the projector in front of a 6.5-kilowatt bulb. The wheel is divided into two parts, each one filtering the projector light into different wavelengths for red, green and blue. The wheel spins rapidly about three times per frame so it doesn’t produce a seizure-inducing effect. The glasses that you wear also contain filters separating the red, green and blue wavelengths for each eye.

The advantages of Dolby’s 3-D system? There’s no need for a silver screen, thanks to the built-in colour-separation wheel and the powerful bulb right next to it, ensuring the bright picture necessary for 3D viewing. Also, a mechanism can be adjusted inside the projector to change the projection method from reflection to refraction meaning cinemas can switch between projecting regular and 3D films.

The cons? The glasses are pricey: more than £15 apiece, so they’re designed to be washed and reused rather than recycled (although, this could be considered a pro for the environment.) Altogether, a Dolby 3D projection system costs cinemas about £16,000, not including the eyewear.

Credits: Wired UK