Time-of-flight camera
This approach has a modular error challenge: measured ranges are modulo the RF carrier wavelength.
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.
[8] Similar principles are used in the ToF camera line developed by the Fraunhofer Institute of Microelectronic Circuits and Systems and TriDiCam.
These cameras provide gating times down to 200ps and enable ToF setup with sub-millimeter depth resolution.
A pulsed laser provides illumination, and an optical gate allows light to reach the imager only during the desired time period.
[10] These devices measure the direct time-of-flight required for a single laser pulse to leave the camera and reflect back onto the focal plane array.
[13][14] Advanced Scientific Concepts, Inc. provides application specific (e.g. aerial, automotive, space) Direct TOF vision systems[15] known as 3D Flash LIDAR cameras.
With a pulse width of e.g. 50 ns, the range is limited to These short times show that the illumination unit is a critical part of the system.
In the diagram of an amplitude modulated array analog timer, the pixel uses two switches (G1 and G2) and two memory elements (S1 and S2).
[4] Because only small amounts of light hit the sensor within 50 ns, not only one but several thousand pulses are sent out (repetition rate tR) and gathered, thus increasing the signal-to-noise ratio.
Here, a second measurement with the control signals delayed by an additional pulse width helps to suppress such objects.
For direct TOF imagers, such as 3D Flash LIDAR, a single short pulse from 5 to 10 ns is emitted by the laser.
As a result, this task uses only a small amount of processing power, again in contrast to stereo vision, where complex correlation algorithms are implemented.
Therefore, if the illuminated scene has a size of 1 square meter, the light from the sun is 50 times stronger than the modulated signal.
For non-integrating TOF sensors that do not integrate light over time and are using near-infrared detectors (InGaAs) to capture the short laser pulse, direct viewing of the sun is a non-issue because the image is not integrated over time, rather captured within a short acquisition cycle typically less than 1 microsecond.
For a phase difference device (amplitude modulated array), due to multiple reflections, the light may reach the objects along several paths.
[22][23] As time-of-flight cameras provide distance images in real time, it is easy to track movements of humans.
[24] The second-generation Kinect sensor originally included with the Xbox One console used a time-of-flight camera for its range imaging,[25] enabling natural user interfaces and gaming applications using computer vision and gesture recognition techniques.
In industrial machine vision, the time-of-flight camera helps to classify and locate objects for use by robots, such as items passing by on a conveyor.
ToF cameras have been used to obtain digital elevation models of the Earth's surface topography,[31] for studies in geomorphology.
In the pulsed method (1), the distance, d = c t / 2 q2 / q1 + q2 , where c is the speed of light, t is the length of the pulse, q1 is the accumulated charge in the pixel when light is emitted and q2 is the accumulated charge when it is not.
In the continuous-wave method (2), d = c t / 2 π arctan q3 - q4 / q1 - q2 . [ 16 ]
