Optical Motion Capture Systems
There are two main technologies used in optical motion capture: Reflective (Passive) and Pulsed-LED (light emitting diodes) Active.
Optical motion capture systems tend to utilize proprietary video cameras to track the motion of reflective markers (or pulsed LED's) attached to particular locations of the actor's body. Single or dual camera systems are suitable for facial capture, while 8 to 16 (or more) camera systems are necessary for full-body capture. Reflective optical motion capture systems use Infra-red (IR) LED's mounted around the camera lens, along with IR pass filters placed over the camera lens. Optical motion capture systems based on Pulsed-LED's measure the Infra-red light emitted by the LED's rather than light reflected from markers.
The PhaseSpace system is an Active LED motion capture system. It achieves phenomenal accuracy via 12 Megapixel cameras at rates of up to 480 frames per second.
The centers of the marker images are matched from the various camera views using triangulation to compute their frame-to-frame positions in 3D space. PhaseSpace’s Active LED technology helps avoid several problems that often plague passive optical systems, including swapping of markers, noisy or missing data and false reflections.
Most systems use a skeleton which is driven by the tracked marker positions as they are captured. The captured skeleton moves around the character's skeleton, which moves the mesh that makes up the skin of the character. This results in animation of the character.
With Passive Optical motion capture systems tracking can be a time-consuming process requiring a lot of operator intervention to clean up and fix problems in the data. Tracking times can range from one to two minutes per captured second of data (clean) to 15 to 30 minutes (or more) per captured second (noisy or complicated data). Most optically based mocap facilities have one price for capture time, and another price for clean-up.
The PhaseSpace system's data is so clean, it can often be used as-is, without the need for further editing.
Optical motion capture systems that use reflective technology to function in real-time are available, but their accuracy is generally less than non-real-time methods. Pulsed-LED based systems provide superior performance in real-time.
Optical is considered the 'high end' of the motion capture field. Passive systems range from $150,000 to $250,000 or more, often requiring a large dedicated space.
The PhaseSpace system’s cost is less than half the going rate for optical motion capture systems, making it a very affordable solution for in-house motion capture.
Optical motion capture systems have the advantage of being very configurable (you can put the markers on an elephant or fabric, or baseballs or footballs, etc.) A large active area is possible, depending on budget and space limitations. Optical systems are useful for capturing gymnastic types of moves. Optical motion capture is most often used 'out of house' at specialty studios, but is very popular for animation for sports games as well as motion capture for film.
PhaseSpace systems are very easy to configure, and can be used in a wide variety of environments, even outside in full sunlight!