ZED2i in night environment


We plan to use the ZED2i camera during night outside.
The camera will be fixed on a robot at a height of about 80cm.
The robot will move at a maximum speed of 8km/h

After calculation, if I want an image without motion blur I need to have an exposure time of around 0.6ms.

Could you give me a magnitude of light (lux or lumens) to achieve such exposure value with ZED 2i?
The target is grass.



Hi @bpasserat
this is a detailed reply that I got from the optics team:

This is a hard question, just to be sure, I think you want to illuminate its grass to have usable images with an exposition of 0.6ms.

The sensor has a sensitivity of 1900mV/Lux-sec and it saturate at 1V. Usually, the noise of the dark current is around 4 dB so to get a correct SNR which would be at least 30dB you need 126mV.
So if you expose 0.6ms you need to have 110Lux on your sensor.

Simplifying the physics you get
Er = L * PI / ( 4 * F#²)
if the grass received an irradiance Ee you get a radiance
L = Ee * albedo(of the grass) / 2PI
grass albedo is around 0.25 so you get
Er = Ee * 0.25 / 32

So the grass would need a really high irradiance to get a good SNR on your camera.
According to my simplification, you need at least 14000lux.

I tested it with a ZED X at 0.6ms with an irradiance of 1320lux and this is the picture I got :

For the ZED 2i you cannot set the exposure time accurately you only have a value between 0 and 100.

It would be more precise with a ZED X because you can control the exposure time directly.

If you cannot have such an irradiance maybe you can consider using a ZED Z One 4K which should be more sensitive and you would be able to choose a lens with a higher aperture.

Thanks for your detailed answer.

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