Cinefex Weekly Update | Issue 45

If glowing festive lights, wheezing steam locomotives and hordes of dancing elves are your bag, Warner Brothers Pictures and Sony Pictures Imageworks have a treat for you this Christmas with their animated fantasy, The Polar Express. Based on Chris Van Allsburg's children's book, the film marked director Robert Zemeckis' ninth collaboration with Ken Ralston, senior visual effects supervisor at Sony Pictures Imageworks. Sharing credit with Jerome Chen, Ralston brought Van Allsburg's book to life using Imagemotion, a new form of integrated face and body motion performance capture, resulting in the all-encompassing title 'imagery and animation by' in the film's credits.

To create the stereo imagery effect -- separate strips of film for right and left eye, projected simultaneously and viewed through polarized gasses -- Imageworks set up a team of 30 animators, led by visual effects producer John Clinton and visual effects supervisor Jim Berney, to analyze stereo options, which proved particularly effective in CG. "There are reasons why 3D works better in CG than live-action," said Hugh Murray, Imax vice president for technical production. "Depth of field is one of them. In the real world, because of physical limitations of optics, cameras can't see everything in focus at the same time. In CG, we can; and in 3D we need everything to be sharp. Another reason 3D is more comfortable to watch in CG than live-action is that cameras don't really exist in CG. They're just mathematical entities. So we had complete freedom to do anything we liked with the distance between the right and left-eye cameras -- the interocular distance -- and that became an animate-able parameter that we controlled constantly through the film."

Zemeckis' cinematic style also enhanced depth effects. "CG animators often use the equivalent of long lenses to avoid CG intersections," said Murray. "Bob didn't do that on this film. That was very fortunate, because long lenses in 3D compress depth in the same way that they compress perspective, and characters end up with that 'cardboardy' look -- flatter than they should be. Instead, Bob chose to use wide-angle lenses, or appropriately-angled lenses, for all of his shots. That gave characters real depth."

The 3D process did not require 2D matte paintings to be altered for stereo effect. "The human visual system uses more than binocular information to judge depth," Murray explained. "We use both eyes to judge depth for objects in proximity; but we found that if we set up a convincing stereo environment, a two-dimensional background was still convincing if it had the correct perspective. The viewer's brain just built it into a scene."