Capturing the movements of a subject is useful for many applications. For example, in the video game industry, movements of a player are used to control the movement and actions of a character in a game. The movement of a subject can also be used in the fields of motion pictures, automatic device control, security, and surveillance, to name a few. Identifying and tracking the movements of a subject is one of the primary objectives of the field of computer vision. Several different technologies have been created to track the movements of a subject.
The technology chosen to track the movement of a subject depends first on the purpose for tracking that subject. Further, the technology chosen depends on several other factors, such as the environment in which the subject is located, the ability to have the subject wear and/or use special equipment, and the desired precision of the tracking. For example, in the motion picture and computer animation industry, motion capture suits are used to track the positions of the subject's joints in high resolution. In home entertainment, video game consoles rely on data from controllers, or other devices, that the subject manipulates or interacts with to track the subject's movements. These devices use accelerometers and/or weight-measuring scales to obtain data about the subject's movements. However, relying on physical sensors and devices has obvious limitations, one of those being that special equipment must be held by or located on the subject. Alternatively, conventional video cameras have been employed to track the movements of a subject. However, robust and reliable joint tracking using conventional video cameras is a very challenging problem. Some of the challenges associated with using conventional video cameras include ambient light changes, segmentation problems, and occlusion.