Specifications

HOW TO SHOOT A LICENSE PLATE WITH A CCTV CAMERA.
When your customer asks you to set up a camera to grab a shot of a license
plate on a car, here are a few things you will want to know.
WHERE TO LOOK.
When setting up a camera to view a license plate, the framing is very
important. You must frame the camera so that the plate will be in the camera’s
view no matter where the plate is mounted on the car, or how the car is positioned
in the roadway. The first trick is make sure you place the camera so that it can
clearly see the numbers and letters on the license plate. Be sure to set the camera
focus control for the sharpest focus. Make sure the plate is large enough in the
scene to be identified. If you can do a good job of this, most installations will work
very well during the daylight.
The camera works well during the day because the light from the sun is
strong and defused, it comes from many sources by reflections off of all the
objects in the immediate area.
THE PROBLEM.
Unfortunately an unaided camera does not do as good a job of reading
license plates at night. They need some assistance to work well under dark
circumstances. Even if the scene were well lit for observation by eye, a car
presents special problems for a video camera.
Often area illumination will be placed immediately over the entrance and exit
gates, a narrowing point just where you would like to see the license plate. Just as
the car enters the gate area, a reflection from the overhead light bounces off the
windshield and blinds the camera. The most common sources of camera blinding
light are the headlights on the car. Any direct light source pointing into the camera
lens at night will cause a camera blinding effect.
The camera blinding effect at the least will result in a loss of detail around
the direct light source, like a blooming effect or halo. At its worst it can darken the
screen so that you will only see the two headlights and everything else on the
monitor will be black and unreadable.
THE CAUSE.
The blooming effect or halo type of loss is caused by the scattering of
electrons on the CCD element inside the camera.
CCTV TRAINING MANUAL PAGE 8 OF 28