As stereoscopic 3-D films grow in popularity, visual-effects supervisors and digital artists face the challenges of creating digital imagery in three dimensions. Unlike the xyz space of the 3-D CGI image, stereoscopic film is made up of two images—representing the right and left eyes—that “converge” to form a single image with depth of field.
HDVideoPro looks into two recent stereoscopic projects to learn about the biggest challenges in creating 3-D VFX and the tricks of the trade in overcoming them.
Journey to the Center of the Earth 3D is based on the classic 1864 sci-fi novel by Jules Verne that takes professor Trevor Anderson (Brendan Fraser), his nephew Sean (Josh Hutcherson) and hired guide Hannah Asgeirsson (Anita Briem) to the center of the earth. Although the picture also was released in 2-D, it comes alive in 3-D, especially in the fantastic visual-effects sequences, full of ethereal sunsets, flying fish with sharpened teeth and massive dinosaurs. The clever and skillful use of effects can, in part, be credited to longtime ILM visual-effects supervisor Eric Brevig, who made the leap to director with this film.
According to visual-effects supervisor Christopher Townsend, the film has 726 visual-effects shots. “That’s the official count,” he says. “But you have to double that number, since each visual-effects shot is made up of a right eye and left eye.”
Stereo Vs. CGI
One of the film’s most challenging visual-effects sequences, according to Townsend, is when Sean realizes he’s beneath a dinosaur when the dinosaur dribbles saliva on him; as the dinosaur pursues Sean, it breaks through a stone archway in an attempt to nab the boy. Persistence Of Vision Digital Entertainment created the sequence as an animatic, which everyone signed off on. “We decided the way to make this work was to create a miniature archway and photograph it,” says Townsend. “We spent months setting up how we were going to do this shot, building various miniatures and testing how it would break apart and building a mandrel, which is the object you use to smash through something that is the shape of the real CG object that will replace it.”
Townsend, like many visual-effects experts, is a big believer in shooting physical elements whenever possible and using CG when there’s no other choice. But, he quickly found the limits of physical elements in creating a stereoscopic effect, especially when the shot includes dust or other atmospheric effects.
The team created a 13-foot-long mandrel of the dinosaur that was articulated and covered in blue cloth so it could be keyed. That was placed on rails that sped down an 80-foot track at 20 mph. Other “real” elements included a third-scale archway and shots of Sean running (on a treadmill). “It looked fabulous as blue-screen elements,” says Townsend.