Motion Capture of Actors Real With Conventional Cameras

Those funny motion capture suits may be a thing of the past. Computer Scientists and filmmakers are working together demonstrating the capability of systems to track and replicate movement with regular video cameras.

While movies like “Pirates of the Caribbean” or “Ted” still combined real actors with digital counterparts, the well-known director Steven Spielberg focused entirely on virtual actors in “The Adventures of Tintin.” He used the so-called motion capture approach, which also animated Ted. Motion capture means that an actor wears a suit with special markers attached. These reflect infrared light sent and received by a camera system installed in a studio. In this way, the system captures the movements of the actor. Specialists use this as input to transfer exactly the same movements to the virtual character.

“The real actors dislike wearing these suits, as they constrain their movements,” explains Christian Theobalt, professor of computer science at Saarland University and head of the research group “Graphics, Vision & Video” at the Max-Planck-Institute for Informatics (MPI). Theobalt points out that this has not changed since animating “Gollum” in the trilogy “Lord of the Rings.” Hence, together with his MPI-colleagues Nils Hasler, Carsten Stoll and Jürgen Gall of the Swiss Federal Institute of Technology Zurich, Theobalt developed a new approach that both works without markers and captures motions in realtime. “The part which is scientifically new is the way in which we represent and compute the filmed scene. It enables new speed in capturing and visualizing the movements with normal video cameras,” Theobalt explains.

Implemented, it looks like this: The video cameras record a researcher turning cartwheels. The computer gets the camera footage as input and computes the skeleton motion of the actor so quickly that you cannot perceive any delay between the movement and its overlay, a red skeleton. According to Theobalt, the new computing approach also works if the movements of several persons have to be captured, or if they are obscured by objects in the studio and against a noisy background.

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