“In one case, Joe knew that he was going to come back and shoot this bluescreen sequence of Viggo Mortensen running on walls. He wanted us to cover the backgrounds for that sequence while we were in Morocco. So, not really knowing what the light angle was going to be, or exactly what he wanted, we started shooting tons of stills. I thought Joe was probably going to want to do a dolly move — he’d want to be running with Viggo. The problem is that if you do a dolly move or a booming move, there are a lot of perspective shifts going on, which you don’t get from a still. So we mocked up different camera moves on the still photos. Once Joe bought the idea that we could move these backgrounds in a 3D way, then we could go out and cover all different angles and lighting conditions, so we were prepared when we came back and actually shot the bluescreens.”

ILM has created previs systems allowing filmmakers to preplan complex scenes on the spot. “We have technology that can put in the digital character or background, all in realtime during the shooting. The system tracks the camera so it knows what the angle is, and then renders in the CG character at the right perspective and angle, so you can see how well everything is lining up. With this, you can test motion capture, and the angle of the background. They used it on A.I. for the City of Sin — a lot of that city was computer-generated. We had a low-res model of the city in the computer, and in realtime we could go around and pick camera angles and then move the 3D model as well, to get nice dramatic scenery. Then, based on that camera information, we put in the real CG city.” Despite the low-res, the system gives a much better sense of what the composition of the shot will be like. It’s a much superior method than just looking at blue screens. I’ve seen uses of it where they are doing motion capture and they actually previs the motion capture into the plate. This way, you can see how that’s going, in real time, as you are working on it, so that if the performance isn’t just right, you’ll know at the moment.”

Ted Rae, vfx supervisor on The Passion of the Christ, used motion control to track the camera movement to recreate the scourging scene in the studio.

A Passion for Details
For the effects work on The Passion of the Christ, visual effects supervisor Ted Rae used motion control techniques in instances where he felt that motion capture was too limited. “The sequence where Jesus is scourged in the courtyard involved digital effects. There are times when the wounds that are revealed were makeup applied to Jim Caviezel’s body and filmed on set. After the film was edited, we covered up the wounds with digitally painted pieces or with real skin elements of a stand-in that were tracked and warped to match Jim’s movements. We then roto-wiped those skin elements off, to reveal the wounds that were already there.”

To add these elements, it was necessary to recreate the scourging scene in the studio. Rae chose to use motion control to track the camera movement. “Caleb Deschanel’s shooting style keeps the camera moving almost constantly. For visual effects, that style can be problematic unless things are well planned and lots of information is gathered on set. When Jesus was moving and the camera was moving it created a lot of axises to start tracking in post. As far as I know, there is no tracking software that can do it, unless you motion capture, and I don’t know of any motion capture system that can track a small portion of a human body with the accuracy that we needed. So there were two problems we had to solve. The first was documenting the camera movement, and the second was deriving the information necessary to recreate how Jesus was moving. I knew that by using motion control, we could accurately recreate, down to a thousandth of an inch, the camera movement. So we took that data and recreated the courtyard set-up back here on stage. But mind you, this was not the set-up for the entire courtyard, but only the area involving Jesus’ body. The make up was then reapplied to a stand-in’s back. Then while watching playback of the motion control camera’s video tap, the stand-in pantomimed the movements Jim had done on set. We blended separate takes together, if necessary, creating photographic elements running in realtime with the same camera speed, shutter angle, lighting, color temperature and make-up. Only then did we manipulate those images digitally during compositing.”