How 3D TV and movies work

Over the past 12 months or so there’s been something unusual going on at cinemas around the country: 3D movies are back and this time they don’t require silly paper glasses with coloured lenses.

What’s even more startling is that, if some companies are to be believed, 3D could soon be coming to a television near you. We take a look at how this would work and ask why you would want to try it.

Why are you seeing double?
In the near future, 3D displays could find their way into homes across the country. There are four types of 3D display, each relying on the same basic principle: 3D requires you to see two different images simultaneously, one via the left eye and the other via the right.

Perhaps the most famous technique uses what are called anaglyph images. Each frame of the film includes two images laid over each other, and coloured red and blue. The viewer needs to wear glasses with red and blue lenses to filter out one of the overlaid images. Red areas on screen will appear as white to the eye covered by the red filter and black to the eye with the blue one.

This system has two obvious disadvantages: it requires the viewer to wear silly glasses and has a huge effect on the film’s ability to show accurate colours. On the other hand, the glasses are cheap to produce and you don’t need a special screen.

Earlier this year the Disney TV Channel showed a concert movie, Hannah Montana & Miley Cyrus: Best of Both Worlds, using this 3D system and released it on a 3D Blu-ray disc with the glasses included. Reviews suggest that the 3D effect isn’t particularly good but then the film itself sounds far worse.

In February, the US television network NBC showed an episode of its drama series Chuck in 3D, that required coloured glasses.

Polar opposites
An alternative method uses polarisation. This restricts the shape of the light waves that we see. Imagine a ray of light as a wave heading away from you. This can be polarised so that as the wave travels it waggles up and down, or from left to right.

In a simplified 3D cinema two pictures are projected on the screen, directly on top of one another: the image for the left eye uses waves oscillating from side to side; the one for the right eye oscillates up and down. The viewer wears glasses with polarised lenses that only allow in the correct type of light, and therefore the correct picture, to reach each eye.

This system looks better than the coloured anaglyph films, and allows colour to be reproduced properly. But it has its disadvantages.

The glasses, which normally use circular polarised lenses rather than the simple filters described earlier, are more expensive to make.

More importantly, this kind of film cannot be shown on a standard television, which lacks the ability to emit polarised rays of light. However, manufacturers such as LG are already making LCD televisions with the necessary equipment built-in.