The secrets of James Cameron's new film Avatar (original) (raw)

In real life, we see images in three dimensions because our left and right eyes see slightly different images that, when combined by the brain, deliver a picture that has depth. In old-fashioned 3D cinematography – the sort where your glasses had red and green coloured lenses – a pair of closely-aligned images with different tints gave the impression of depth by fooling the eyes. But modern 3D films have developed new techniques to drag them out of their B-movie past, and Avatar takes things a step further by using both computer generated imagery and advanced stereoscopic filming methods to create the illusion of reality.

So far, most successful 3D movies have been entirely animated – and Cameron, too, has used computer generated images to build his virtual world. Avatar's footage is built from around 70% CGI, including the female lead, a blue alien played by Star Trek's Zoe Saldana. As a result, the cast donned motion-capture suits – essentially, leotards covered in sensors that feed the movements of the body back to a bank of computers – and acted out their scenes on a "performance capture" stage six times bigger than anything used in Hollywood before.

Cameron also attempted to crank up the realism by improving the way the suits captured the actors' facial expressions, using a skull cap with a camera enhancement that closely monitored their eyes, mouth and other small movements.

Motion capture makes 3D much easier, not just because it allows film-makers to add the special effects later, but also by letting them position the "camera" (actually a viewpoint from inside the virtual world), wherever they want. If the director wants to shift the angle to the left or right, it's done with a click of the mouse and the computer then works out what it would look like. In most ways, the technique is more closely aligned with the way that high-end computer games are developed rather than traditional Hollywood productions.

One major advance with Avatar's setup was the creation of a virtual monitor that allowed the director to see the motion capture results in real-time, as they were filmed, instead of waiting for the computer to render the images.

Cameron spent much of his own time and a significant amount of money upgrading the systems used for Avatar, but he hasn't just used 3D for the computer-generated portions of the film: new techniques were also created for the live action parts.

Working with long-time collaborator Vincent Pace – founder of a camera equipment outfit in Los Angeles – Cameron developed a filming rig that is more advanced than anything that has gone before. The setup consists of a number of stereoscopic cameras that each use a pair of lenses built to mimic human eyes – positioned close together and able to move a little in order to focus on objects that are nearby or far away. That allows the cinematographer to capture two images simultaneously, which align perfectly with and provide the illusion of depth.

Filming is just one element of creating a 3D movie, however. The other part – which most people are more familiar with – is viewing it in the cinema. Here Avatar is less revolutionary. Although most of tomorrow's trailers will be shown on the giant, high resolution Imax screens, the audience will be using the same technologies used for recent 3D films such as Bolt, Coraline and Polar Express. Viewing not only requires a digitally equipped cinema (sometimes with a silver-coated screen to boost the brightness), but also that stalwart of three dimensional cinema: a pair of special glasses.

But instead of old fashioned coloured lenses, modern 3D films require audiences to wear polarised glasses – where each lens lets through a slightly different kind of light. This means that your left eye and right eye can see different images shown simultaneously on the screen – and not only are they less headache inducing than in the past, they look much more like ordinary specs too.