  Time-of-flight (TOF) cameras are sensors that can measure the depths of
scene-points, by illuminating the scene with a controlled laser or LED source,
and then analyzing the reflected light. In this paper, we will first describe
the underlying measurement principles of time-of-flight cameras, including: (i)
pulsed-light cameras, which measure directly the time taken for a light pulse
to travel from the device to the object and back again, and (ii)
continuous-wave modulated-light cameras, which measure the phase difference
between the emitted and received signals, and hence obtain the travel time
indirectly. We review the main existing designs, including prototypes as well
as commercially available devices. We also review the relevant camera
calibration principles, and how they are applied to TOF devices. Finally, we
discuss the benefits and challenges of combined TOF and color camera systems.
