We’ve all seen BTS footage of Marvel or Sci Fi action stars swimming in mid air in front of a green screen covered in multiple tiny dots stuck to a black bodysuit. While this makes the actor look rather silly, it’s important to look beyond that in order to truly understand the artistry that is motion capture.
The Rokoko Smartsuit Pro is an example of one of these suits and uses inertial sensors to broadcast the location of devices embedded inside the suit. Used in games and movies you’ll see optical tracking of markers where the camera uses to look for high contrast areas.
Jimmy Corvan at House of Moves (Injustice, Spiderman) explains that this isn’t really super high and the small balls you see on suits can be bought fairly cheaply on Amazon.com. It isn’t so much the balls that enable the tech they just enable the camera to see movement really clearly. It’s just retroreflective tape!
The footage shot of actors wearing these tapey-balled suits is fed through software then interprets what the camera sees before artists review it. Advanced suits, such as those worn by Mark Ruffalo for The Hulk, also have additional symbolised stickers to let the software know more about the location of the suit on the performer.
“The first step in the cleanup process is somebody goes through and makes sure every dot in every frame can be seen. It sounds tedious because it is!” Corvan told Vox “this person also properly names each marker. This process is called tracking and labelling.”
For hobbyists there are free to download softwares which can figure out the motion of a person without the need for balled suits but the output is still similar. The software calculates what makes up the skeleton and joints which is what enables it to translate the motion.
Often in the media, we are asked to focus on the actor’s portrayal of an animated character but there is months and months of work involved before the filmed human performance becomes what we see on the big screen. Animators must adjust elements of the performance due to issues with size and timing (Mark Ruffalo is of course nowhere near the size of the hulk, for example). The work put in is what makes animation feel real. Without that it’s just joints and bones!