Ideal Night-time IP Camera

[moheat]

I'm looking to get a CCTV setup to get a clear night-time number-plate capture of slow-speed (~20 mph) vehicle across 10 meters. The area has a decent amount of ambient light via street lights.

Since ANPR and LPR cameras can get pricey, I was wondering what specifications I should be looking for in order to get a good enough IP cameras in terms on Focal length, Frame rate, bitrate, resolution, features, etc.

I was considering DS-2CD2T47G3E-L, it's a 4MP 1/1.8" sensor 6mm local length camera. Please let me know if this would work for my context. Thank you!

 

[TonyR]

Calling LPR guru @wittaj ......

 

[wittaj]

You need to have the proper angle to see plates (the camera needs to be able to see the plate), shutter speed, and the correct focal length for the distance to be covered.

Generally below 30 feet one can go with a varifocal up to 13mm

Between 30 feet and 60 feet one should go with a varifocal up to 32mm

Between 60feet to 200 feet one should go with a varifocal up to 64mm

These distances can vary based on the size of the plate and the angle. If you have a straight on angle (cars are directly approaching) you can get by with a little less focal length.



Streetlights don't really play a part unless you have a lot of light.

Keep in mind that this is a camera dedicated to plates and not an overview camera also. It is as much an art as it is a science. You will need two cameras. For LPR we need to OPTICALLY zoom in tight to make the plate as large as possible. For most of us, all you see is the not much more than a vehicle in the entire frame. Now maybe in the right location during the day it might be able to see some other things, but not at night.

At night, we have to run a very fast shutter speed (1/2,000) and in B/W with IR and the image will be black. All you will see are head/tail lights and the plate. Some people can get away with color if they have enough street lights, but most of us cannot. Here is a representative sample of plates I get at night of vehicles traveling about 45MPH at 175 feet from my 2MP 5241-Z12E camera (that is all that is needed for plates):

See the LPR subforum for more details.

 

[moheat]

Gotcha. Yeah I already have a camera setup for general purpose observation and I'm only looking to get plates right now.

Do you think the specifications of the camera I mentioned would do fine?

 

[wittaj]

It would be close. Personally I would opt for a varifocal with at least 12mm focal length for that distance.

 

[moheat]

Gotcha, thank you!

 

[moheat]

It would be close. Personally I would opt for a varifocal with at least 12mm focal length for that distance.

Also, do you think fps matters that much when it comes to capturing night-time plates? Is there much difference between a 20fps capture and a 30fps capture?

 

[bigredfish]

Actually LPR is one place FPS can come in handy. I run 30FPS

The vehicle is only in the scene for maybe 1/2 to 1 1/2 seconds. More frames gives me more opportunities for a good plate. on any kind of angle, you'll see a difference between frame #1 and frame #20. Speed will make a difference


Frame 12 and 23 - total time plate in scene .95 seconds

 

[wittaj]

And on the flip side I run LPR at 8FPS.