Number Plate Camera Hi Resolution
Number Plate Recognition Cameras are quite different compared to a standard security CCTV or IR type Camera. Our 12V NPR Cameras are designed for one main purpose, to see a Number Plate regardless of whether the vehicle headlights or tail lights are on or off either day and night. The special built-in illuminators highlight the actual plate and lower the intensity of the headlights to achieve the desired result.... Number Plate identification.
NPR or Number Plate Recognition is a high-resolution colour camera by day however, by night this device is like no other. The NPR will auto switch to B/W mode, necessary for the built in IR illuminators to brighten a licence plate sufficiently for the numbers and letters to be read. Fundamentally that is the role of this security camera.
A standard CCTV Camera or IR camera realistically can't see a number plate at night and if it does it more luck or coincidence. Car headlights and tail-lights are simply too bright for standard CCTV cameras to see. A typical IR camera is NOT designed to read a registration number, particularly at night. By day that is not a problem for most security cameras, night is the issue.
Our NPR Cameras on the other hand are designed to have the "opposite effect" to a standard CCTV camera. By day the NPR Camera will be colour or similar to a High resolution CCTV camera. However, by night this camera auto switches to B/W mode so the area under surveillance is highlighted with an invisible illumination similar in many respects to a night club “black light” which illuminates white to make it stand out above all other colours.
To a standard CCTV camera, headlights and tail lights are too bright but to our NPR camera, those same lights are automatically dimmed whilst the actual number plate is illuminated to make the plate stand out like a beacon so to speak. It’s equally important to realise that the NPR is not designed to see people at night, especially if they are standing in the dark. This is NOT a night vision surveillance camera; it is designed primarily to see licence plates or number plates. If there is a need to see people including number plates by night, then two separate cameras should be installed.
To see and read a number plate at night, it’s equally important the NPR camera is mounted within a reasonable range of the vehicle; say 5-15m at most and not mounted too high or low. Ideally the NPR camera should be no higher than 2-3m high and aimed as much as possible toward the front of rear of the approaching or leaving vehicle.
Digital Video Recording System
Whilst any camera can be cabled to a TV monitor for a live view, in most cases the customer will need the event to be recorded along with the number plate. Its critical in NPR recording and identity that the recorder is equally high specification and at the very least H.264 D1 real time. If for any reason the number plate becomes obscured, provided the DVR recorded the motion activated event, to see the plate clearly simply advance forward or backward frame by frame up to 25 times per second to capture and review the number plate. If the recorder is low quality and not real time then the ability to enhance and zoom in on the plate could potentially fail.
Hidden Camera Surveillance offers a range of suitable DVR systems in H.264 codec from D1 through to the newer HD and IP systems.
Behaviour of Reflected Light
To explain some further technology behind successful NPR capture we need to look at the behaviour of light. A basic law of light is that the angle of incidence equals the angle of reflection. However, number plates have a special characteristic known as RETRO-REFLECTIVE. The surface is covered in hundreds of tiny hemispheres that cause light to be reflected back to the source. This is the same technology used in safety clothing and signs. No matter from which direction the light is directed, it always reflects back and makes them very visible.
Application of Infrared Illumination to NPR If a standard colour or monochrome camera was focused to read number plates it would have to contend with a huge variety of lighting conditions, daytime, night-time, sunlight, backlight, headlights, and so on. One configuration simply would not cope with all conditions, so there is a need to provide a constant level and direction of illumination irrespective of any other conditions. And so we come to the development of special cameras for continuous capture of number plate data. The camera must be sensitive to the infrared part of the spectrum, to at least 850 nanometres. Then it must be fitted with a filter to restrict the visible part of the spectrum. The lens would have a manual iris set fully open and the shutter speed set to 1/1000th second. Finally an infrared source must be fitted adjacent to the camera or embedded within. Therefore, taking advantage of the retro-reflective characteristics of number plates, the illumination from the illuminator will be reflected directly back to the camera. Thus only infrared light will be seen without any visible light or other reflections or refractions. The picture will of course be black with no detail except for the number plate.
What Can I expect from an NPR Camera Day or Night?
The images below depict what the user can expect when the ANPR Camera is correctly positioned and alighned to take full advantage. Taking a broader view is fine but remember, the camera illuminators MUST be aimed at the vehicle registration plate and illumination distance must be taken in to consideration. For that reason we recommend not exceeding manufacturer distance requirements. As mentioned previously, the quality of the camera and the recording quality is paramount otherwise there is no point.
NPR Camera Angle Views