Fox’s newest blockbuster franchise, Fantastic Four, is a superhero saga that’s all about characters- that’s why it was critical that the film’s lead VFX house, Giant Killer Robots (GKR), figure out a way to keep Chris Evans’ winning performance as Johnny Storm on screen, even when the character transforms into the flaming Human Torch. "We didn’t want him to be just an amorphous fireball," says GKR’s Peter Oberdorfer, VFX supervisor on the film. So the team used extensive motion-capture sessions to create a " Chris Evans /Human Torch" rig that could be animated and match-moved to fit Evans’ facial and body movements.

"That allowed us to transition seamlessly between the real and the CG Human Torch," Oberdorfer explains. "We would go to the virtual character, but make it a seamless transition as Evans approached the camera or said a line. It also allowed us to hang our effects precisely over Chris’s performance. Even though the effect was 20 or 30 layers thick, with fire and surface and plasma and heat distortion, you still wanted to see the performance through all that. With a really accurate tracking rig, we had the best of both worlds- the realism of a facial performance, and the kind of crazy effects you couldn’t get with a live actor."

The system was implemented for the entire show, in an effort to maintain each actor’s performance as their character transitioned from live action to CG and back again. "That meant we had to be very rigorous about capturing the data for those transitions," Oberdorfer says. "We had eight angles of seamless, timecoded video from our motion capture sessions that we could synchronize and make sure everything was lining up visually. It was a laborious capture process, but in the end we saved tons of time in production. We still had a team of 10 to 12 match-movers working through the shots and allowing us to have a virtual rig. We could modify the performance if we needed to, replacing body parts, but you want the real performance, because the audience can detect a CGI person pretty easily."

The Human Torch was animated in Maya and rendered in Mental Ray on a mixture of Linux- and Wintel-based machines. "Once you get into the Torch flying around in a virtual environment, you’re talking about a 90- or 100-layer comp. We try to control most of our process in the digital composite, so we can make alterations on the fly should we need to color-correct it or remove part of it. It’s much quicker to do that all in 2D after we generate the 3D imagery."