Motion capture technology records movement digitally and is used in entertainment to make non-human characters more lifelike. There are four main input methods: prosthetic, acoustic, magnetic, and optical. Optical motion capture is the most popular and allows for a larger performance area. It offers benefits such as real-time results and the ability for an actor to play many roles.
Motion capture technology is a process by which movement is digitally recorded. The technique was originally used for military tracking purposes and in sports as a tool for biomechanical research that focused on the mechanical functioning of the body, such as how the heart and muscles work and move. Over the past twenty-five years, this technology has become an essential tool in the entertainment world, giving computer animators the ability to make non-human characters more lifelike. It is a technology used in animated films, television and video games.
Historically, motion capture in animated films has been created using an extension of the rotoscoping technique. In this technique, an actor is filmed making certain movements or gestures while wearing markers on specific points on his body. Each marker in each frame of film is then manually encoded into the computer. As animation software improved, it became possible to apply an algorithm to markers that connect them to a 3D object, creating what is now called motion capture.
Techniques for capturing motion may vary based on input methods; there are four main input methods: prosthetic, acoustic, magnetic, and optical. Prosthetic or mechanical motion capture uses trigonometry to input data from mechanical devices attached to the performer’s body. Due to the inhibitory nature of the machinery, it is rarely used today.
Acoustic motion capture uses audio transmitters on the actor’s body that make a clicking sound when triggered by movement. Receivers measure the time it takes for sound to reach them and triangulate the data to indicate a point on a 3D plane. While the acoustic method does not encounter some of the problems of the optical method since a line of sight is not a problem, it does have other potential problems including audio interference which affects the accuracy of the acquisition.
Magnetic motion capture is one of the most commonly used methods. This approach uses a central magnet and several receivers attached to the actor’s body. The receivers capture and record the movements of the actors and save them on the computer. This technique can be hampered by nearby metal objects if they are large enough, and depending on the strength of the magnets used, the capture area may not be as large as one would like.
Today, optical motion capture is probably the most popular method. This approach uses at least three cameras and adequate lighting to recreate the actor’s position in a 3D space. It allows for a larger performance area and less inhibited movement than the other methods. Due to the cost of each camera, this approach is probably the most expensive of the four.
Motion is the first and fastest way humans perceive visual information, so motion capture offers a number of benefits to the filmmaker concerned with authenticity. It’s a much faster way to film than rotoscoping and can deliver real-time results. Also, because the process only records movement versus physical features, it allows an actor to play many roles. Perhaps most importantly in terms of realism, the accuracy of the data allows complex movements to be replicated with the correct weight distribution and force exchange.
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