CCTV effective distance to read a number plate.

[chili-girl]

For a normal CCTV camera (that is linked to a PC capture card) and on a fine sunny day.

Is there a typical distance you can read a number plate.

With one of the SafeCore CCTV 1/3" SONY Colour WDR & ICR(True Day&Night) Camera (Hi-Res.) cameras 752x582 picture element, 520 lines resolution, 0.1 Lux / F1.2 day, 0.001 Lux / F1.2 at night with IR switching and with effective IR illumination.

Lens fitted is a 1/3" 3.5-8mm Vari-Focal Lens, DC drive auto iris Aperture: F1.4

1 - Is there a typical distance you can read a number plate. 2 - Would I then be able to read a number plape at say 25m. 3 - What would the picture be like at night with IR on, or are they just too grainy 4 - Or are my problems only due to the PC capture card.

[Andy Burns]

Depends on the focal length of the lens ...

Assume you need the plate to be approx 10% of the image width to read the plate (giving approximately eight pixels per character on the plate) lets round the plate dimensions up to 1.5', so you need a field of view of 15' to achieve the plate being 10% of the image.

For a 1/3" sensor you'd need a lens of 26mm focal length to give a field of view of 15' at a distance of 82', unfortunately your 3.5-8mm zoom lens isn't going to cut it.

[Andy Burns]

Just to say a bit further ... if you *did* have a 25mm lens to make the plate readable it wouldn't make a very good CCTV as you'd only see the car and immediate surroundings, rather than an all round view, which is why council/police CCTV have pan/tilt/zoom cameras and an operator.

[Alan]

It may need a lens with a longer focal length (longer than 26mm) as the camera/lens combination has a resolution lower than a pixel count suggests.

At night power of the illumination at 25m would have to be adequate and a ' ring of leds' would probably be insufficient.

The alternative is to get some software such as is used in CSI where you will be able to read a whole number plate from a single pixel in the source video.

[Vortex3]

Q1 Agreed with Andy above you need at least 8 pixels per character.

Q2 To be pedantic:

• A 1/3" sensor has a size of 4.6 x 3.8mm

• Using an 8mm lens the field of view at 25000mm will be:

• (25000/8) * 4.6 = 14375mm wide

• Sensor has 752 horizontal pixels.

• 14375/752 = > 19mm per pixel. you really need

[Andrew Gabriel]

I haven't tried at quite that distance, but at shorter distances, number plates (and rear reflectors) appear extremely bright because of the way they reflect light back to the source. Actually, this can cause the auto-iris to close up such that the number plates and reflectors are the only items clearly visible in the field of view at night.

;-)

[Andrew Gabriel]

Not any that I've seen. Actually, I was quite intreagued to discover when I started playing with them that the switch to IR night vision is not globally across the whole image, but depends on the lighting level at each part of the image. A dark part of the image will be in B/W night mode (subject to there being enough IR lighting), whilst a light part of the image will be in day colour mode.

and nasty consequences for trying to take a full frame still image from such a camera. You will end up with two images overlaid on alternate lines which are 20ms apart. I spent some time with photoshop once sliding alternate lines to get a good picture of a suspect which was originally too blurred to recognise, but then became instantly recognisable to the police.

[The Natural Philosopher]

I thought that was spooks and numbers..

[Vortex3]

Do you own one of these cameras, or were you just thinking of buying one?

You see coincidentally I was just about to list a camera on eBay that might be interesting to you....(accept my apologies for being presumptuous)

Text:

This camera is a good bit of kit but DOESN'T have a night mode.

Ping me if interested. I was hoping to convert it into enough money to buy a takeaway. That's all!

D

[Andy Burns]

Doesn't it have a filter for de-interlacing? GIMP does ...

[nightjar]

At the entrance to our industrial estate there are five CCTV cameras, set up by a security company. Two colour cameras give short range pictures of the gate, in opposite directions. Two colour cameras give long views of vehicles approaching the gates. One high definition monochrome camera captures the number plates of vehicles entering the estate - you don't need colour for number plates and monochrome is capable of both higher definition and lower light response. It is set about3m high and looks down at about 30 degrees. Steel bollards guide the vehicles through the gateway, ensuring that the number plates are in the field of view. At night, the area is lit by 2 x

150W high pressure sodium street lamps, as one did not provide enough light.

Colin Bignell

[Andrew Gabriel]

Oh, it might do now. This was some years back, Photoshop 4 or 5 era. Photoshop 5 is the last version I bought.

[Matty F]

During the day you may get to read a number plate if the vehicle is moving slowly and it's only a few metres away or you have a very good telephoto which you can point straight at the front or rear of the vehicle.. With all the CCTV cameras I've used, about one third of the plate is blurred over the rest, making it unreadable. At night I once managed to read a plate, only because the car was almost stopped about

5 metres away. What I'd like is an infrared flash that flashes 25 times per second all night, but I've not found one yet. I may try to make one using a spinning wheel and some infrared LEDs. If the plates are reflective a few LEDs will reach 6 metres or so.

Look up "trail camera". There are some with an infrared flash that take a photo when movement is detected.

Otherwise an ordinary digital camera focussed to infinity will take excellent flash photos up to 50 metres away for a moving vehicle. If the vehicle is not moving, a three second exposure focussed to infinity using a tripod will get plate numbers at night without using the flash.

[Dave Plowman (News)]

Yup. Very clever that. Now all they need is the software to sort out the appalling direction on last night's episode of 'New York'.

[Owain]

Megapixel IP CCTV camera is probably what is needed. Much more controllable, with the camera able to do its own motion detection and record different resolutions at different times.

's a quiet, but fairly responsive, forum on the site as well

Owain

[Clint Sharp]

In message , Andrew Gabriel writes

Got one on the desk in front of me. There are plenty out there that do exactly this and they can give excellent results for reasonable prices. They've been around for five or six years that I know of and possibly longer.

[Vortex3]

The issue with IP cameras is the compression they use.

The danger is that all the high fequency data is trashed, and therefore the plate in this instance would be illegible anyhow.

D

[tony sayer]

They seem a tad expensive for doing it over IP?...

[Mark]

Have you considered the legal or ethical implications of this? I know the "Big Brother" philosophy seems to have spread everywhere now and spying is acceptable. But, I for one, don't agree.

Forgive me if I have got the wrong end of the stick here.

[Matty F]

Catching crooks is a good way of slowing them down from committing more crime.