By Henry Martel, Field Applications Engineer, Antaira Technologies
License plate recognition (LPR) makes it possible to detect, read, and store the image of a vehicle’s license plate.
Such technology has numerous applications—it can facilitate traffic control and electronic toll collections, improve security in private sector industries such as hospitals or museums, and serve as a crime deterrent.
To accomplish these many useful tasks, LPR relies heavily on the use of highly innovative and advanced cameras.
How license plate recognition works
License plate recognition works by capturing a video of a vehicle’s license plate through an advanced camera. The video is stored for review or analyzed using optical character recognition software and then referenced against a database of other collected license plate numbers. Such systems greatly improve the efficiency of manual license plate recording methods.
The role of cameras in license plate recognition
Cameras play a substantial role in the process of license plate recognition. Essentially, the facilitation of LPR hinges on the images that cameras take, which are then used in optical character recognition. If the camera is not able to take a quality image, then the entire LPR system is essentially useless. As such, the camera is arguably the most important component of any license plate recognition system.
Types of cameras used in LPR systems
Depending on the application, LPR systems may use many different types of cameras, such as infrared cameras, mobile cameras, closed-circuit television cameras, and existing road-rule enforcement cameras.
However, most license plate recognition systems come equipped with specialized cameras that cater to their specific task. That said, as software techniques develop the capability to support any IP-based surveillance camera, the need for such specialization is decreasing. As a result, the capability to use LPR systems in perimeter security applications is quickly increasing.
Deployment measures for LPR cameras
In their original implementation, LPR cameras primarily adhered to light posts at intersections. Such an application allowed them to connect easily with the traffic control network of a given city. However, as LPR technology evolves, its various methods for deployment are greatly expanding.
Rather than just installing the LPR cameras in a stagnant location, they now have various mobile applications as well. For example, many police vehicles use LPR cameras, and mobile drop systems can use them to capture images of license plates while in motion.
Challenges for cameras in license plate recognition
Several challenges pertaining to cameras can emerge in the process of license plate recognition. Some of the main trials that LPR systems face in relation to capturing quality images are as follows:
- Speed of vehicles: Because the license plate recognition often captures moving vehicles, blurry images can result. In some cases, the images are too blurry to read, which negates the effectiveness of the license plate reader. For the camera to record a clear image, the speed of the oncoming vehicle must be slow enough to allow the camera to focus on the license plate. The maximum speed at which a vehicle may be traveling for a camera to successfully capture an image will largely depend on the lighting, the quality of the camera, and the distance of the camera from the vehicle.
- Poor lighting: Another substantial challenge that LPR cameras face is poor lighting that makes it difficult to capture a quality image. The lighting in most LPR application environments is largely uncontrollable. Factors such as varying levels of ambient light due to weather changes, harsh reflections, shadows, or headlight glare can affect the quality of any images it captures.
- Obstructions: Obstructions also pose a challenge for LPR cameras. If dirt, debris, a tow bar, or other types of obstructions obscure even part of the license plate, it can be impossible for even the highest quality LPR camera to capture a readable image of the license plate number.
- Harsh environmental conditions: Often, LPR cameras reside in areas that experience various harsh environmental conditions. From intense heat to severe inclement weather, the cameras and the networks backing them must be robust enough to withstand a range of unforgiving environments without faltering.
- Lane changes: If a vehicle changes lanes while the LPR is in the process of scanning its license plate, the camera may not be able to focus properly. As a result, the image that it captures may not facilitate an accurate reading.
Requirements for license plate recognition cameras
To mitigate the above challenges and ensure that the images captured by license plate recognition cameras are suitable for optical character recognition, the system must meet several requirements. Some of the main requirements for cameras that are used for license plate recognition include:
- Industrial-grade networking equipment: The network used to backhaul the information and deliver power to the LPR cameras has a substantial impact on how effective the license plate reader is. Because the LPRs often reside in areas that experience harsh environmental conditions, the system must connect to industrial-grade networking equipment.
- Proper positioning: Proper camera positioning also plays a large role in the effectiveness of license plate recognition. If threshold angles of incidence are exceeded between a camera and the target capture area, the ability to obtain a viable image will decline drastically. As such, it is important to carefully consider the angle and height of the LPR camera prior to installation.
- Additional lighting: To mitigate the issues presented by poor lighting, many LPR cameras must come equipped with infrared illumination. However, even when using a camera that has infrared capabilities, it is important to install additional lighting surrounding the camera to ensure that it can capture a quality image.
- Fast shutter speeds: to minimize blurring as much as possible while capturing images of moving objects, the LPR cameras should use incredibly fast shutter speeds. Ideally, the shutter speed should be set to around 1/1000 when capturing fast-moving vehicles. If the camera is capturing a license plate on a vehicle that is navigating in slower traffic, the shutter speed can generally be around half of that speed.
Antaira Technologies is a leading developer and manufacturer that provides high-quality industrial networking and communication product solutions. Since 2005, Antaira has offered a full spectrum of product lines that feature reliable Ethernet infrastructures, extended temperature tolerance, and rugged enclosure designs. visit www.antaira.comantaira.com