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Capturing License Plates

Chapter Video Surveillance Made Easy e-book

How to Capture License Plates with Security Cameras

License Plate

One of the most common needs our customers has is the ability to identify vehicles on or near their property. This can be achieved if you follow the rules and recommendations we detail below. It is important that you follow them simply because capturing a license plate is one of the most challenging tasks a video surveillance system is asked to do. In fact it’s easier to get facial recognition than it is to capture a license plate. But the advice below will solve the challenges and produce the desired results.

Understanding the Challenges

The environment creates several challenges that may have to be addressed to capture moving license plates.

Slow Down

Speed of the Car
The average speed the cars will be traveling is an important factor in which camera to use. It is best to select a targeted area that requires the car to reduce its speed as much as possible. If the car is traveling faster 20 miles an hour you will require a specialty license plate camera that has the ability to adjust shutter speeds so the image does not blur. If the vehicle is traveling under 20 miles an hour the task becomes much easier.

If the speed is above 20 miles an hour your choice of cameras will be limited to a few cameras specifically designed to capture license plates. Even high definition "HD" cameras will not solve the speed issue. Cameras specifically labeled "License Plate Camera" have the shutter controls needed. If you are working with slower speeds several of our cameras can achieve the desired results.

Camera Location
The location of the camera to the cars path is very important. If the camera is placed at too much of an angle from the plates path no camera will proved the results needed. The best location for a camera is one that allows the camera to view the approaching or leaving plate perpendicularly (as close to direct on as possible). The easy way to test the camera location is to simply park a car at the location you plan to capture the plate, and then stand at the camera location. If you can clearly read the plate the location should work.

Viewing angle

Dedicated Camera
The most common mistake made is to ask one camera to do the work of three. Often a customer will expect to view their driveway; see the persons face in the car and read the license plate. Each one of these tasks require a different field of view (or focal length). Usually the camera is set to a wide viewing angle to see as much as possible; completely eliminating the ability to capture the detail needed to read a license plate. So here is the Golden Rule: One camera MUST be dedicated to ONLY reading license plates! This will allow you to adjust the field of view specifically for this task assuring success.

One of the reasons plates are difficult to capture is the head lights and tail lights. At night the camera has a difficult job balancing between the darkness and the intense lights of an on coming car. The solution for capturing plates at night is to use a camera designed specifically for License Plate Capture; they have back lighting adjustments which eliminates the glare. Most HD cameras can easily capture plates during the day but there is no guarantee of successfully capturing plates at night. As the example below shows the camera with back lighting eliminates the glare but the HD camera does not.

Glare examples

Selecting the Right Camera
There are two distances that matter when choosing the right camera for your application. A) the distance from the camera location to the location you expect to capture the plate. B) the horizontal viewing distance at the location of the plate.

Horizontal Distances

Both distances can be accommodated by using a camera with a "manual zoom lens". The manual zoom allows you to mount the camera and then zoom the cameras field of view in or out until the maximum horizontal distance is achieved.

As the chart below indicates, using a 2.8 to 12mm lens will allow you mount the camera 60 feet way from the plate location and still achieve a horizontal field of view of 18 feet.

Zoom Lens Chart

The maximum horizontal distance recommended is a function of which technology you are using. This is because each technology records in different resolutions. For example the old technologies such as analog CCTV, produces a very low resolution requiring you to have a very small horizontal field of view as the chart below indicates. Using our new HD technologies a much wider horizontal field of view can be used and still capture crisp clear images of license plates.

Based on this information we recommend the following maximum viewing distances. You may be able to have larger horizontal viewing distances and still capture plates but the guide below is safe and reliable. Each application is different and the environment may favor larger distances.

The following MAXIMUM horizontal distances should be followed for best performance.

Max Horizontal Distances

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