Three-dimensional (3D) motion tracking is the act of capturing motion data from actors and actresses. This is similar to filming a person moving around, but the difference is that, instead of footage that can only be played back, 3D motion tracking records the movements so they can be applied to 3D rendering programs. Performing the capture requires special hardware, such as suits and tiny tracking units, but some systems just need a camera to capture the motion. A subset of motion capturing, called performance capture, deals with extremities and facial features.
The act of 3D motion tracking is similar to filming people moving around, but the difference is in how the information is handled. With filming, the footage can only be watched, while motion capture is a digital model of the motion that can be applied to 3D figures on a computer. This is most often used by the movie industry when creating 3D animated films or when computer-based models require intricate movement. Motion tracking also is used by the military to build virtual exercises and by engineers to control machines.
Special hardware is required to perform 3D motion tracking. In the past, actors and actresses were fitted with suits and small tracking units, and a camera tracked their movement. This hardware is still used frequently, but more advanced systems are able to capture motion data without the need of trackers, known as markerless tracking. A special camera is still needed to translate all movements into digital signals and information.
The practice of 3D motion tracking deals with how the limbs and torso move, but not the finer details of human movement. For finer details, performance capture is used. This type of tracking obtains data from finger and facial movements, so artists controlling the 3D model have intricate data about these movements. Without this information, artists have to create facial expressions and finger movements from scratch, which can lead to awkward expressions or stiff hands and fingers.
Before 3D motion tracking was available, animated film artists in the past used a similar system, called rotoscoping, to track motion. Actors and actresses were filmed performing movements and speaking lines according to the script. Artists would then take the film and draw over each frame individually. This resulted in more realistic animation, because all the movements were based on real people. Most major animation companies, before the advent of the 3D motion tracking, used rotoscoping.