COMPUTERS IN ANIMATION SHERBERT JAMES BRIDGES 04-24-2000 THE USE OF COMPUTERS IN
ANIMATION The use of motion capture for computer character animation is relatively new, having begun in the late 1970's,
and only now beginning to become widespread. Motion capture is the recording of human body movement (or other
movement) for immediate or delayed analysis and playback. The information captured can be as general as the simple position
of the body in space or as complex as the deformations of the face and muscle masses. Motion capture for computer character
animation involves the mapping of human motion onto the motion of a computer character. The mapping can be direct, such as
human arm motion controlling a characters arm motion, or indirect, such as human hand and finger patterns controlling a
characters skin color or emotional state. The idea of copying human motion for animated characters is, of course, not new.
get convincing motion for the human characters in Snow White; Disney studios traced animation over film footage of live actors
playing out the scenes. This method, called rotoscoping, has been successfully used for human characters ever since. In the late
1970's, when it began to be feasible to animate characters by computer, animators adapted traditional techniques, including
rotoscoping. At the New York Institute of Technology Computer Graphics Lab, Rebecca Allen used a half-silvered mirror to
superimpose videotapes of real dancers onto the computer screen to pose a computer-generated dancer for Twyla Tharp's
"The Catherine Wheel." The computer used these poses as keys for generating a smooth animation.
Rotoscoping is by no
means an automatic process, and the complexity of human motion required for " The Catherine Wheel," necessitated the setting
of keys every few frames. As such, rotoscoping can be thought of as a primitive form or precursor to motion capture, where
the motion is "captured" painstakingly by hand. Having seen the possibility of animating characters by performance techniques in
Waldo C. Graphic, and Videosystem, a French video and computer graphics producer, turned the attentions of its newly
formed computer animation division to the problem of computer puppets.
The result was a real-time character animation system
whose first success was the daily production of a character called Mat the Ghost. Mat was a friendly green ghost that
interacted with live actors and puppets on a daily childrens' show called Canaille Peluche. Using DataGloves, joysticks,
Polhemus trackers, and MIDI drum pedals, puppeteers interactively performed Mat, chroma-keyed with the previously-shot
video of the live actors. Since there was no post-rendering, animation sequences were generated in the time it took the
performers to achieve a good take. Seven minutes of animation (one week's worth) were normally completed in a day and a
half of performance.
Mat appeared on Canaille Peluche every day for over three and a half years. Video systems, now known
as Medialab, has continued to develop the performance system to the point where it is a reliable production tool, having
produced several hours of production animation in total, for more than a dozen characters. Typically, several puppeteers or
actors working in concert control each character. Two puppeteers control the facial expressions, lip-synch, and special effects
such as shape transformations for Mat the Ghost, or bubbles from the mouth of a fish, and an actor mimes the upper body
motions while wearing a suit with electromagnetic trackers on the torso, arms, and head.
The finger motions, joystick
movements, and so on, of the puppeteers are transformed into facial expressions and effects of the character, while the motion
of the actor is directly mapped to the character's body. In the past few years, Ascension, Polhemus, SuperFluo, and others
have released commercial motion tracking systems for computer animation. In addition, animation software vendors, such as
SoftImage, have integrated these systems into their product creating "off-the-shelf" performance animation systems. Although
there are many problems yet to be solved in the field of human motion capture, the practice is now well ensconced as a viable
option for computer animation production. As the technology develops, there is no doubt that motion capture in computers will
become one of the basic tools of the animator's craft.