ANPR (automatic number plate recognition) is a system of cameras and software that reads a vehicle's number plate as it passes, so a car park or toll road can charge its owner with no ticket or booth. The same technology is used to open a gate for known vehicles and to find vehicles on a police list.
Here is how it works in general. A camera takes a picture of the vehicle, often with infrared light so that it works at night. Software finds the plate in the picture, cuts out the characters and reads them using computer vision. The result, for example "MH 12 AB 1234", is checked against a list or an account. The system then acts: it opens a barrier, adds a charge or sends an alert. The image and the number are stored as evidence.
Accuracy depends on the camera angle, the speed of the vehicle, the light and the state of the plate. Plates in India have used many fonts and layouts over the years. The high-security registration plate, which has a standard font and a hologram, is easier to read. A vehicle image is personal data, so operators keep it only for a limited time and protect it. A wrong read can charge the wrong person, so a person should be able to correct it.
Take, for example, a mall car park. A camera reads the plate when the car enters and again when it leaves, and the system charges for the time spent. The driver has no ticket to lose. Consider a barrier-free highway toll point where cameras read the plate of every vehicle. If the toll cannot be collected from the vehicle's FASTag, the owner receives an electronic notice to pay; see electronic tolling and toll back-office systems. Imagine a residential society that opens its gate for registered residents; see gate visitor approval.
The plate is sometimes dirty, bent or in a different font, so the system gives a confidence score and sends doubtful reads to a person. Cameras are often combined with RFID, and the processing is usually done near the camera, as in edge computing. Related pages are parking and video analytics.
How is it different from RFID? ANPR reads the plate that every vehicle already carries. RFID needs a tag to be fixed to the vehicle.
Appears in
- Smart parking and kerb management↗ Urban mobilityA camera reads a car's number plate at the mall's entry and exit and charges the owner's account for the time.
- Electronic tolling↗ Fare collection and tollingA camera reads the plate of a vehicle with no working tag and sends the toll or a notice to the owner.