Motion Capture – What, how and why If there were a technology to resurrect the dead, bring to life extinct and inanimate characters, Motion Capture (Mocap) would be among the main contenders for the prime spot. Motion Capture, defined as the technique of digitally recording the movements of real things so that their movements can be played back with computer animation has moved into the realm of reality. What is Motion Capture? Simply put, Motion Capture is the recording of human body movement (or other movement) for immediate or delayed analysis and playback. It is the process of capturing the movement of a real object and mapping it onto a computer generated object. Usually, Motion Capture is used to create synthetic actors by capturing the motions of real humans. This technique is used in cinema and video games to create amazingly real effects. Growth of Motion Capture By the 90s, special effects and fantasy was passé for the western audience. Till this time, computer graphics technology had come a long way and with powerful processors, rendering improved, textures were richer, movements smoother, and lighting effects more realistic. Realism was required to rein in audiences. Filmmakers then turned to technology to try and create dead or extinct creatures, and even complete digital characters. However, would these digitally created characters merge with the real ones on screen? The answer came with Steven Spielberg‟s „Jurassic Park‟ where dinosaurs and pre-historic animals blended perfectly with live footage. With the unprecedented success of this movie, it was proved that with the right technology and sufficient computing power it was possible to digitally resurrect dead actors or extinct animals in films. Taking the concept of virtual characters further, in the movie Forrest Gump, actor Tom Hanks meets president John F. Kennedy, long since dead. In India, Pentamedia Graphics embarked on a movie that promised to digitally reincarnate the deceased stars Raj Kapoor and M.G. Ramachandran through motion capture and motion creation technologies and bring them together on the silver screen. The process of Motion Capture An actor wears a leotard with numerous reflective markers taped or glued to specific points over his body. At least two or more cameras film the actor as he acts or performs specific motions. These cameras report to a computer the exact position of each reflective marker, many times per second. A motion capture session only records the movements of the actor, not his visual appearance. These movements are recorded as animation data, which is then "mapped" onto a 3D model (which can be of a normal human or anything else) that was created by a computer artist, and the model can then be made to perform the same movements that were recorded. An alternative to the above is the use of a magnetic system, in which the actor wears a number of sensors, which detect a nearby magnetic field and transmit data on each sensor's inferred 3D position to the computer. These camera motions are also tracked meticulously and fed to the computer; or, a computer controlling the camera motion has already been programmed with the motion control data, and the camera meticulously follows the directions of this computer. This computer then uses software to post-process this mass of data and determine the exact movement of the actor, as inferred from the 3D position of each marker at each moment. After post-processing, the computer exports animation data, which computer animators can associate with a 3D model and then manipulate using normal computer animation software such as Maya or 3D Studio Max. Types of Motion Capture Mechanical The performer wears a human-shaped set of straight metal pieces (like a very basic skeleton) that is hooked onto the performer's back; as the performer moves, this exoskeleton is forced to move as well and sensors in each joint feel the rotations Other types of mechanical motion capture involve gloves, mechanical arms, or articulated models (like Monkey), which are used for 'key framing' Optical The performer wears reflective dots that are followed by several cameras and the information is triangulated between them The markers are either reflective, such as a system manufactured by Vicon or Motion Analysis, or infra-red emitting, many of which have been developed for musical applications (such as conducting) These are developed primarily for biomedical applications (sports injuries, analysis of athletic performance, etc.) Electromagnetic The performer wears an array of magnetic receivers that track location with respect to a static magnetic transmitter Often this type of motion capture is layered with animation from other input devices One of the first uses was for the military, to track head movements of pilots Advantages of Motion Capture The great advantage of Motion Capture over traditional animation techniques such as keyframing and simulation is the capability of real-time visualization and the high quality (natural looking) of the generated animation. Motion capture allows the shooting of scenes that are unrealistic or dangerous to replicate in real life. It helps avoid cumbersome procedures involved in re-shooting of scenes that have been damaged or requiring changes. Motion Capture scores over traditional animation in terms of the time taken to animate a character. Due to the very nature of the technology used, Motion Capture can capture nuances with more detail than traditional animators would have. In fact, this is among the prime reasons that Motion Capture animation seems so realistic. Additionally, difficult physical movements, especially that involving simultaneous movements can be more accurately depicted than by animators who may not be able to simulate the movement. Careers in Motion Capture Says R. Krishnan ,Global Head, Arena Animation , “The beauty of Motion capture is the ability to capture movement with such incredible accuracy that even foreground characters on the big screen are lifelike and this is quite visible in films like Jurassic Park, Titanic, Gladiator, The Mummy, Pearl Harbor to name a few. The applications of this technology are enormous and can be limited by only one‟s imagination.” In India the film industry is increasingly employing sophisticated motion capture techniques. However the experts in this area are few. Motion capture for computer character animation is fast gaining popularity and leading institutes such as Arena Animation offer courses in Motion Capture, which is increasingly becoming popular as a career. An exciting future ahead Current technology limitations mean a motion capture session only records the movement of a few key points on the actor's body, where the sensors or reflective markers are placed. In the coming days, future technology may include full-frame imaging from many camera angles to record the exact position of every inch of the actor's body, clothing, and hair for the entire duration of the session, resulting in higher resolution of detail than at present. Indranil Basu Academic Head – North & East Arena Animation
"3d Motion Capture"