"So we either had to do a face replacement for every stunt done in the desert or add the digital actors in the vehicles," Rocheron suggests. "Originally, we thought we could get away with 2D face replacement solutions, but very quickly we realized that some of the shapes of the stunt double's heads were very different or the hairlines didn't match. And because the vehicles are moving a lot into the environment, the lighting changes quite a bit.

"So we decided to build full-on 3D digital doubles and roto'd in all the actors and vehicles and put our digital actors in there and we traced the head with a 3D version of it. There was even one shot where we had great second unit footage of a fight with Paul Walker on the truck, and they really wanted to keep the shot so we had to replace the stunt double's face, which filled two-thirds of the screen.

"The other challenge was to marry the greenscreen photography with the desert photography. What production did was shoot tialed backgrounds in the desert with three different cameras at different speeds, at different angles, on different locations, at different distances from the trucks. We could then stitch that footage and create some environment bubbles in Nuke, which we could basically apply on the greenscreen footage. We would get forced perspective and dust from the desert and we really could match the environments as seamlessly as possible."

And, of course, when Diesel and Walker do the jump in the canyon with the Corvette, it's a mix of real stunt work and CG replacement and enhancement. "The stunt was used actually for having a practical hit in the water and practical splashes with the car and the guys," he adds. "We took off the practical cliff that was 50-feet-high and replaced it with one that was 300-feet and it looked more like a desert type of canyon.

"There's a bridge in the sequence, which is also digital. Nobody would really build a bridge like this with those sheets of concrete footing, but we used different references that we patched together that work well for the section that fits onto the desert as well as the section that fits above the canyon itself.

Bill Desowitz is senior editor of AWN & VFXWorld.