Some background: By the time Fincher started thinking seriously about the film, he and Digital Domain had worked together on numerous features and commercials. The Button team was an oiled machine, which allowed the director to focus on storytelling, not technology. "We've been working with Fincher for 15 years," says Ulbrich, who served as executive producer of VFX on Button. "There's a shorthand, a trust with him and his team (including DP Claudio Miranda, editors Angus Wall and Kirk Baxter and AD Bob Wagner). "What that does is minimize the process and technique and gives him creative flexibility; instead of solving effects problems he's focusing on the material." As for Fincher's interest in the project, he says, "I like the idea of a movie where the special effect is time. How do you show time in the background or time in the foreground and have it subtly etch its way in people's faces and change the background of the world we see them in. The size of that canvas was an interesting thing."
By 2004, DD and Fincher had started working on Button in earnest. That year they provided Paramount a one shot proof of concept video and got the green light (Ulbrich jokes that at that moment he excused himself to go and be sick—they actually had to do this thing now). The central challenge was to ensure that Pitt (rather than an animator's interpretation of Pitt) was actually playing the character throughout his life—from wizened man of 80-ish through his 70s and 60s to the actor's current age and beyond (Pitt played the character until he reached childhood. VFX company Lola provided "youthening" effects that made the actor appear onscreen as his unlined younger self). Given that mandate and the additional challenge of the difference in body size and type between Brad Pitt and the Benjamin character (who appears as a small, stooped old man in the early part of the film), traditional animation/head replacement techniques created too many opportunities for the character to fall into the dreaded "uncanny valley" (the creeps people get when looking at a being that appears almost but not quite human).
In a rather large nutshell, here's how they did it. The first thing to know: after the initial shots of the animatronic infant, the next 52 minutes of Pitt playing Benjamin do not contain any Pitt—it's animation (until the real actor appears in make-up on the tugboat bound for Russia. A total of 325 shots of animation. VFX shops Hydraulx and Asylum also contributed many elements to the film).
Fincher shot the film (with Viper cameras) using smaller, blue-hooded actors in place of Pitt. Make-up artist Rick Baker created three painstakingly detailed maquettes (models based on casts of Pitt's face) that represented the actor at ages 60, 70 and 80. DD then created digitized versions of the maquettes. Character supervisor Steve Preeg and Barba turned to what's known as FACS (Facial Action Coding System, a body of research by psychologist Dr. Paul Eckman that categorizes the full set of universal human expressions) as a starting point for Pitt's performance. DD used the Mova Contour system to capture Pitt performing that gamut of facial expressions. "When we first looked at doing this movie in 2004 we had something in our original R&D plan that was not dissimilar to what they built," says Barba. "When they presented their system we looked at each other like, 'they did it.'" The technology was still in its early days and Kreeg worked with the company to develop the system to fit Button's requirements. Mova's markerless system represented a significant advance in performance capture, creating a high def, "volumetric" representation of a face (or other surface). Performer's faces are covered in phosphorescent makeup and captured by a multi camera rig—this eliminates the sort of interpolation that happens with a system that uses a number of markers placed on the face to capture data.
Pitt (the whole Pitt) was also shot by multiple cameras performing the role of Button and DD artists matched the CG expressions to his overall live action performance. And then? Well, DD retargeted Pitt's captured expressions onto CG versions of the appropriately-aged maquettes, of course—hand animating where necessary, says Barba, to get the nuances right. And that's just getting started—DD faced monumental challenges in terms of tracking and compositing and lighting, in many cases building proprietary systems to accommodate the level of difficulty and to ease workflow. Through it all, Barba says the biggest challenge was managing the team. "We've all been looking at faces since we were born; we just know when something isn't right. Artists can't always put a finger on it and maybe can't verbalize it. You get a shot that's 95 percent there and that last five percent can be really challenging especially with a talented group saying what they think is wrong." For Fincher, the process revolved around making audiences care about Benjamin—recreating an organic life form "wasn't as important as creating a character for a moment. That's the most interesting thing for me—it had nothing to do with the shaders. It's, Oh my god he wins me over in this moment.
DD is currently at work on projects that will advance the tech and systems used on Button. "It's a game changer," says Ulbrich. "It'll be difficult to do a less realistic character now." And yes, you will see the technology used in commercials. "With computer-based visuals there's a belief that anything is possible as long as you have enough time, money and resources," says Ulbrich. "In advertising there's just never enough. It's a big advantage for our advertising clients to have tools available to them that would otherwise be cost and time prohibitive to develop for a single spot or campaign."