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Concept
Time-of-flight camera
Summary
A time-of-flight camera (ToF camera), also known as time-of-flight sensor (ToF sensor), is a range imaging camera system for measuring distances between the camera and the subject for each point of the image based on time-of-flight, the round trip time of an artificial light signal, as provided by a laser or an LED. Laser-based time-of-flight cameras are part of a broader class of scannerless LIDAR, in which the entire scene is captured with each laser pulse, as opposed to point-by-point with a laser beam such as in scanning LIDAR systems.
Time-of-flight camera products for civil applications began to emerge around 2000, as the semiconductor processes allowed the production of components fast enough for such devices. The systems cover ranges of a few centimeters up to several kilometers.
Several different technologies for time-of-flight cameras have been developed.
Photonic Mixer Devices (PMD), the Swiss Ranger, and CanestaVision work by modulating the outgoing beam with an RF carrier, then measuring the phase shift of that carrier on the receiver side. This approach has a modular error challenge: measured ranges are modulo the RF carrier wavelength. The Swiss Ranger is a compact, short-range device, with ranges of 5 or 10 meters and a resolution of 176 x 144 pixels. With phase unwrapping algorithms, the maximum uniqueness range can be increased. The PMD can provide ranges up to 60 m. Illumination is pulsed LEDs rather than a laser. CanestaVision developer Canesta was purchased by Microsoft in 2010. The Kinect2 for Xbox One was based on ToF technology from Canesta.
These devices have a built-in shutter in the image sensor that opens and closes at the same rate as the light pulses are sent out. Most time-of-flight 3D sensors are based on this principle invented by Medina. Because part of every returning pulse is blocked by the shutter according to its time of arrival, the amount of light received relates to the distance the pulse has traveled.
The distance can be calculated using the equation, z = R (S2 − S1) / 2(S1 + S2) + R / 2 for an ideal camera.
Official source
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