How Stereo 3D Works

Stereo 3D (S3D) is becoming more and more commonplace in our lives - in movie theatres, in public spaces such as bars, and in our living rooms.

But how does it work?

The basics are, in fact, very simple. Two very similar two-dimensional images are made to look like a single three-dimensional one; an illusion of depth for the person viewing them. The principle applies to still and moving pictures.

To get an idea what's going on, hold your finger a short distance from your eyes. Consider that each eye is seeing a slightly different view of your finger, but your brain integrates these two views and interprets them as a single three-dimensional view. If you close one eye after the other, you can see the differences between the 'left' and 'right' views of your finger.

S3D is like your visual system

S3D uses the same approach. Two HD cameras are mounted approximately the same distance apart as your eyes - the distance can vary in practice, if the film- or program-maker wants to achieve particular effects.

The left and the right eye signals are kept separate throughout the post production process and the display technology presents each signal to only the correct eye so that the brain 'sees' the depth present on the original scene.

The real points of interest are the creative possibilities of having a third dimension to play with. In the realm of special effects, there is the now almost traditional monster leaping out of the screen at the audience, or a building falling towards them.

Using depth cues

Filmmakers have used depth cues almost since the earliest films. They're equally applicable in two-dimensional programming as in three. But the simple act of directing an actor to walk behind a car, for example, will reinforce the illusion of depth being built by the interaction of the two images and the person watching the S3D film.

On-set monitoring and post-production

Although S3D is now established as a technology, it can be difficult to anticipate the effect on-screen because film- and program-makers are dealing in optical illusions. While many makers still shoot and then check during post, most agree that a 3D monitor on-set is what's really needed.

The director can then be fully confident that the 3D effects being tried for will work exactly as anticipated. If playback on-set shows the shot hasn't worked, then it can be reshot right away, potentially saving an enormous amount of time and money.

With the digital files safely shot, post-production is the next stage in content creation, with the most advanced technology currently offering creative people a huge degree of freedom in delivering their vision for movies, TV dramas, commercials or documentaries.

S3D TVs and Movie Projectors

TVs and projectors decode the S3D datastream from pro storage devices or Blu-ray discs into two separate images. The pictures are refreshed very rapidly, switching between the two images. The images on the screen are then synchronized with the stereo glasses worn by the viewers. So-called active shutter glasses block one eye and then the other, so that each eye only sees the image that is meant for it.

The alternative is to use polarizing technology. Using polarized images and polarizing glasses, different images can be fed to each eye as each lens accepts correctly polarized light, but rejects incorrectly polarized light.

Glasses-free systems have already been developed and demonstrated, and the industry is looking forward to further impressive growth as later adopters who have reacted against the need to wear glasses buy into Stereo 3D at home and in public.

David Throup is R&D Group Leader at Quantel. The company develops innovative, world-leading content creation systems for broadcast, post and DI. Quantel products deliver at SD, HD, 2K, 4K and S3D. Learn more about 3d editor equipment.