Optical Motion Enlivens Videos

Brent D. Johnson

The entertainment industry is in the midst of a revolution. The artificial world of video games has been enlivened by animated figures that gasp in an imagined atmosphere and strain under the pressure of a counterfeit gravity. A company called the House of Moves, which inspirits animated creations with the odd narrative of human movement, is spearheading this revolution.

To achieve realistic motion in animated movies, actors wear tiny spheres wrapped in reflective tape. Their motion is captured by high-resolution, high-speed CMOS video cameras, and the data is triangulated for 3-D representation.

Optical motion capture technology was initially used by orthopedic surgeons to perform gait analysis on their patients. Today it has grown beyond the clinic and has taken up residence on the soundstage, where athletes and actors alike commute their bodies to digital form by animating 3-D characters.

The movement of actors is recorded by an array of synchronized, high-speed video cameras that have an integral LED strobe unit. Light reflected from markers affixed to the performers supplies real-time 2-D position data. The data runs to a centralized station connected to another PC, which triangulates it and generates an accurate 3-D representation. After the information is processed, clients attach the motion data to computer-generated models, and the models move like real people.

The most significant technology on the data-collection side has been the sensors. House of Moves uses 24 MCam2 1.3-megapixel cameras from Vicon with a maximum capture rate of 1000 fps. One of the major advantages of the system is that it allows an unlimited number of reflective markers, produces a large capture volume, and does not use wires or transmitters that might entangle the performer. Vicon calls its capture technology a passive optical technique: passive because the markers on the performers are spheres covered with reflective tape, and optical because high-speed, high-resolution CMOS video cameras provide the 3-D data.

A challenge for this business is that the data must be delivered in any format the client needs, so all 3-D software packages must be supported. Jarrod Phillips, vice president of sales and marketing at House of Moves, said that the company is "software-agnostic" but tends to work with Maya from Alias Wavefront and 3D StudioMax from Discreet Products the most. Diva, the in-house software, is used for hardware motion capture data cleanup.