Method for controlling a light source in a night vision surveillance system
AssigneeChung-Shan Institute of Science and Technology
InventorsShiaw-Shiang Jiang, Chunn-Yenn Lin, Guang-Hann Liou
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Abstract
A method for controlling a light source in a night vision system is provided. The method first computes a pulse width Tp=2(d−d1)/c, where c is the light speed, according to parameters of a desired observing distance d and a shortest distance d1 of the back-scattering light that enters the light sensor, such as a low-light-level camera. According to the definition of duty cycle D, it is determined by D=(1−d1/d)/(2−d1/d). According to the parameters of the desired observing distance and the pulse width, control signals are generated by a pulse signal controller to control a pulsed active-light illuminator with proper emitting period and a gated light sensor with proper gated-on period.
Claims10
A method for controlling a light source in a night vision system, which comprises a pulsed light illuminator and a gated light sensor, the method comprising:
- estimating or measuring a desired observing distance d of an object;
- setting a shortest distance d1 for back-scattering lights to enter the light sensor;
- determining a pulse width Tp of a light beam emitted from the pulsed light illuminator, in which Tp=2(d−d1)/c, where c represents a light speed;
- determining a duty cycle D for the pulsed light illuminator, wherein D is equal to Tp/(Tp+T2d), where T2d=2d/c;
- the pulsed active-light illuminator emitting light pulses with the pulse width Tp and an emitting period (Tp+T2d);
- and
- the light sensor receiving the light pulses which are reflected by the object, wherein the light sensor has a sensing period identical to the emitting period but with a delay time of T2d.
A night vision system to observe an object at an observing distance d from the night vision system, the night vision system comprising:
- a pulsed light source used to periodically emit light pulses, each of the light pulses comprises a light beam with respect to a pulse width Tp for each of the light pulses;
- a gated light sensor used to periodically receive the light pulses reflected by the object;
- and
- a pulse signal controller to produce an illuminating signal and a receiving control signal to respectively control the pulsed light source and the gated light sensor so as to periodically emitting and receiving the light beam,
- wherein each of the light pulses is controlled to have a duty cycle of D = T P T P + T 2 d = 1 - d 1 d 2 - d 1 d ,
- where d1=d−(Tp/2)c and T2d=2d/c, so that the illuminating control signal controls the pulsed light source to emit the light pulses in an emitting period of (Tp+T2d) and the receiving control signal controls the gated light sensor to receive the reflected light pulses in a receiving period which is identical to the emitting period but has a delay of T2d.
Dependencies are inferred from the claim text.