ToF camera uses active light detection, which usually includes the following parts:
1. Unit of irradiance
The irradiating unit needs to pulse the light source before emitting, and the modulated light pulse frequency can be as high as 100MHz. Therefore, during the image capture process, the light source will be turned on and off thousands of times. Each light pulse is only a few nanoseconds in duration. The camera's exposure time parameter determines the number of pulses for each imaging.
To achieve accurate measurement, the light pulse must be precisely controlled so that it has exactly the same duration, rise time and fall time. Because even a small deviation of just one nanosecond can produce a distance measurement error of up to 15 cm. Such high modulation frequency and precision can only be achieved by using sophisticated LEDs or laser diodes. Generally, the illuminating light source is an infrared light source that is invisible to the human eye.
2.Optical lens
It is used to gather the reflected light and image on the optical sensor. However, unlike ordinary optical lenses, a band-pass filter is needed to ensure that only light with the same wavelength as the illuminating light source can enter. The purpose of this is to suppress incoherent light sources to reduce noise, while preventing the photosensitive sensor from being overexposed due to interference from external light.
3.Imaging sensor
The core of ToF camera. The sensor structure is similar to the ordinary image sensor, but more complicated than the image sensor. It contains 2 or more shutters to sample the reflected light at different times. Therefore, the pixel size of Tof chip is much larger than that of general image sensor, generally about 100um.
4.Computing unit
The calculation unit can record an accurate depth map. The depth map is usually a grayscale image, where each value represents the distance between the light-reflecting surface and the camera. In order to get better results, data calibration is usually carried out.
