Principle of Time of Flight 3D Camera

https://upcommons.upc.edu/bitstream/handle/2117/13573/1232-Lock-in-Time-of-Flight-(ToF)-Cameras_-A-Survey.pdf

A near-infrared light (NIR), via light-emitting diodes (LED), is emitted by the system

and then reflected back to the sensor. Many authors [9]–[12] provide formulations for sinusoidal signals, although other periodic functions can be used. Every pixel on the sensor samples the amount of light reflected by the scene four times at equal intervals for every period, (m0,m1,m2 and m3 in Fig. 1), which allows for the parallel measurement of its phase