Need advice on suitable ip camera for reading licence plates

[storpotäten 0]

Hello all,

My first post here.

I've been trying to grasp what specs are required to get a camera which can show accurately enough the licence plate of a parked car (or better: slowly approaching car) about 50 feet away.

I want an IP camera (which will be connected to my pc through a PoE switch...I know computers and switching/networking very well so that part is not my worry). The camera will be mounted fixed, and I have no need to move/pan it sideways or anything like that. I want to watch the driveway in front of my house, and I'm quite sure I am more interested in a relatively narrow angle than the wide-angle. I have currently no need for nightvision/IR or anything similar.

 

If I understand correctly one of the most important things is the lens focal length. The higher value, the better. And of course the resolution of the camera.

 

My budget is limited and I would prefer something less than 500-600 USD. I think I want a camera capable of recording at least 720p at 30fps.

 

First I was considering Axis M1054 but it has only 2.9mm (0.11in) focal length (see link at the end of this message). I assume this means the camera is not as suitable for reading license plates compared to cameras with focal length of, say, 8mm (5/16 in) or more. Next I found Axis M1114 which has a variable focal length 2.8-8mm. A third option is Zavio D7210 with focal length up to 10.5mm (almost 7/16 inch).

 

Would you consider any or all of these suitable for my needs, or would I have to go to even better cameras?

I'm not sure if I'm on the right track here. Am I paying too much attention to focal length?

 

Any advice would be most apprieciated.

Regards

Storpotäten

 

Specs Axis M1054: http://www.axis.com/en/products/cam_m1054/index.htm

Specs Axis M1114: http://www.axis.com/en/products/cam_m1114/index.htm

Specs Zavio D7210 : http://www.zavio.com/product.php?id=62

[SunnyKim 2]

I'd better buy two, in stead of one expensive one, just in case one fails to read the number correctly.

[mgb 0]

I think you'd be best with one of the varifocal models so you can really set it in on the sweet spot.

The problem is that with getting license plates properly, your aim will be lower and you may not get a view if the overall area.

This is why, a true license plate setup would involve two cameras. One aimed tight at the plate are and one for overall area.

There are also specialized LPR cameras.

I would say you'd be better off with a 2 or 3MP rather than a 720P if you are looking to get coverage of the whole vehicle.

[buellwinkle 0]

None of the cameras you mention would be good for what you are asking to do.

 

I'm using Hikivion cameras at one location for license plate recognition (LPR) which is a lot harder to do because you have to have an image that can be processed to text for alerts and logging than what you are ask which is to view a license plate. For one location, we are using a ds-2cd2732f which is a 2.8mm to 12mm varifocal, but the car has to pass the camera at about 20'. Camera runs $259 so well within your budget.

 

Also, what I did for longer range viewing is swapped lenses on an inexpensive Hikvision ds-2cd2032-i with a 25mm lens and that allowed me to clearly read a plate at 50'. Here's some shots at 45' in a completely dark area in my backyard. While the camera is capable of 3MP, I have to keep resolution low, at 640x480 to reduce CPU demands of doing LPR. We use Milestone LPR for the software. If you want to go this route, PM me, I can give you more details.

 

 

 

At night, to overcome headlights, tail lights and reflection off the plate I had to set the exposure to 1/200/sec, otherwise the plate would look white with no numbers.

 

[MaxIcon 0]

The lens length will depend on the distance you need to read plates at and the conditions. You can't get much more than 25mm on an M12 lens camera, especially bullet cams. Longer lenses are physically very long, and the f-stop drops at longer lengths.

 

What you need is a certain number of pixels per foot. In the US, a car plate is 1' wide, and if you measure the character stroke width, you'll find you need 40 pixels per foot if everything is ideal. Everything's not ideal, of course, so you'd want to go to 60 ppf for overhead.

 

At night, you'll need more, and you'll need to worry about exposure time, as BW mentioned. You'll find plate illumination varies quite a lot, including lights off, plate light on, taillights vs brakelights on for rear plate, and headlights on or off for front plates.

 

Also, those numbers hold if you're getting the image straight on. If it's at an angle, like if your watching the street from the front of your house, you need even more resolution, as the virtual plate width is lower. This also extends the distance you need to be able to read at.

 

BW's post above looks great at 45', because he's getting 90 pixels per foot. If you can get this in a straight-on capture, you should have few problems.

 

I'm testing a similar setup, using 1080p for more pixels per foot on a Hik 2032 with a 1/2" 25mm lens, and at 100' and about a 30 degree angle, I can read plates fine in the daytime, but as soon as the lighting drops, the resolution fades. At night, they're unreadable on the Hik, because its low light image quality isn't good at the exposure times you need to avoid image blur and avoid plate washout.

 

A cam with better low light performance would help, but if you want to do it with a high likelihood of success, you'll need some dedicated hardware. BW has some good posts on how to do serious LPR with serious hardware.

[buellwinkle 0]

We use a 50mm lens on an Axis Q1604 for LPR and it's marginal at about 75'. Nice camera for LPR though, get the indoor version as the outdoor version housing can't take that lens. So figure $800ish for the camera, $100 or so for the lens, $300 for the Axis housing. Fujinon also has a lens that goes to 80mm, good for 100' for sure. These are CS lenses, not M12 like the lower end cameras.

 

For grins, this is with default settings at night which is 1/30/sec. While you can still barely read the plate number, add head or tail lights and it will be washed out completely.

 

[storpotäten 0]

Thanks, guys! I found your replies very illuminating and useful for my decision. Much appreciated.