CODEWITHSUNDEEP
opencvcomputer-visionmeasureopencv3.1
AeroClassics
AeroClassics

Reputation: 1124

Can the frequency of a flashing light be counted using a video camera

Is there a formula to determine that max flash rate countable by a video camera? I am thinking that any flash rate > # of fps is not practical. I get hung up on the fact that the shutter is open only a fraction of the amount of time required to produce a frame. 30fps is roughly 33.33ms. If the shutter is set for say 1/125 which is about 8ms or roughly 25% of the frame time. Does the shutter speed matter? I am thinking that unless they are sync'd the shutter could open at any point in the lamp flash ultimately making counting very difficult.

The application is just a general one. With today's high speed cameras (60fps or 120fps) can one reliably decide on the flash rate of a lamp. Think alarm panels, breathing monitors or heart rate monitors or the case of trying to determine duty cycle by visual means.

Upvotes: 0

Views: 944

Answers (1)

marcoresk
marcoresk

Reputation: 1965

What you describe is related to the sampling problem. You can refer your problem to the Nyquist - Shannon theorem Given a certain frequency of acquisition (# of FPS) you can be sure of your counting (in every case, no matter of syncronization) if

"# of FPS" >= 2* flashing light frequency (in Hz)

Of course this is a general theoric rule, things can work in a quite different way (I am answering only regarding the number of FPS in a general case)

Upvotes: 1

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