How Motion Capture Works

Computer-generated images have traveled a long and bumpy road. What was once a cheesy intrusion into a film has become something we can’t imagine a summer blockbuster without. And motion capture technology makes CGI even more lifelike. We sat down with Ruben Moller, a researcher and session instructor at Emily Carr University’s Integrated Digital Studios, to learn just how this mystical Ping-Pong® ball technology works.

As the name implies, it captures the motion of a real actor. However, it doesn’t take the place of a real animator, who still has to labor over the results to create a mind-blowing finished product. Yet, we’ve come a long way. “It used to take 10 days to move a character 100 frames,” explains Moller. “Now we can do that in ten seconds. It doesn’t replace animation. It embraces it.”

Intrigued? Keep reading and checking out images from the mo-cap-driven hit Starship Troopers: Invasion, coming to Blu-ray™ and DVD August 28th (available for purchase now on iTunes®), see more at Action Unleashed. Then impress/annoy the hell out of your friends by explaining everything while watching it.

1. Pick a system

There are two main ways of doing motion capture: magnetic and optical. Magnetic is the cheaper system often used by smaller studios. The actor is covered in magnets and put in a space relatively free from magnetic interference. “The problem is when people have metallic stuff on their clothes—belt buckles, buttons, whatever—that throws off the calculations,” notes Moller. By contrast, optical revolves around people in black Spandex suits and strategically placed, glow-in-the-dark Ping-Pong® balls. “The Ping-Pong® balls are easier to follow.”

2. Suit up and film

Now it’s time for the actors to get into their leotards. These make it easier to track the Ping-Pong® balls fastened to their bodies. “You only need three good sources to have a clear view,” says Moller. Still, many studios will use several cameras. Quick, jerky natural motion can get lost easily; multiple cams ensure that filmers get the subject from three different angles. Otherwise, crisp 3D motion would be impossible to capture.

3. Boot up and render

Fortunately, the animator doesn’t have to pick out the three best shots to make a composite. A computer program—a very expensive one—handles that task. Motion Builder is a popular program that then takes this processed information and brings it to life once the animator selects points on the character corresponding to the Ping-Pong® balls. The character will now be moving something like the physical actor, but the job isn’t done yet. Now it’s time for the human element.

4. Let a human take over

An animator now has to clean things up. Why? Because the first run through doesn’t look so hot. “It’s too jerky,” observes Moller, “It’s real. It’s correct. But it’s boring. The skills of the animator are still needed.” Moller likens the first round of animation to a gu shot. “A movie gunshot sounds nothing like a real gunshot.” Moller states that the role of the animator isn’t just to smooth out the jerkiness, but also to humanize the character. Which sure comes in handy when it comes time for that character to blast a bunch of bugs…