In the world of Automatic Number Plate Recognition (ANPR) software, the connection between the camera and the software plays a pivotal role. After all, the camera is the instrument responsible for capturing the critical footage containing the license plates of vehicles, which is then analyzed and processed by ANPR software. Whether it’s for traffic monitoring, access control, or traffic enforcement, selecting the right camera is essential to achieving the desired results.
Many people mistakenly believe that any camera can be used in conjunction with ANPR software. While this notion might hold true for certain applications like access control in well-lit environments with slow-moving vehicles, it’s crucial to emphasize that employing standard IP cameras for ANPR can lead to significant issues, especially when dealing with fast-moving traffic.
One of the primary reasons why standard IP cameras are ill-suited for ANPR applications involving moving vehicles at high speeds lies in the type of image sensor they employ—the rolling shutter sensor. To understand the implications of this, it’s essential to differentiate between rolling shutter and global shutter sensors.
Rolling shutter sensors capture images by scanning them sequentially, row by row, from top to bottom. This scanning process occurs over a short duration, which may result in image distortion when capturing fast-moving objects like vehicles. In ANPR applications, this can lead to the partial or inaccurate recognition of license plates, especially when vehicles are traveling at speeds exceeding 50 km/h.
On the other hand, global shutter sensors capture the entire frame simultaneously, ensuring that every pixel is exposed at the same time. This technology eliminates the distortions and inconsistencies that can occur with rolling shutter sensors when capturing fast-moving objects. Global shutter sensors are, therefore, the preferred choice for ANPR applications, as they provide stable and accurate images of license plates, even at high speeds.
Another crucial factor to consider is the presence of Infrared (IR) illumination in the camera. While standard IP cameras may offer IR LEDs for night vision, they may not be optimized for ANPR purposes. This becomes particularly problematic when dealing with retroreflective license plates commonly used in many regions. Retroreflective plates reflect light directly back to its source, making them highly reflective. In such cases, standard IP cameras with IR illumination may wash out the characters on the plates, rendering them unreadable.
Furthermore, for successful ANPR applications, a proper ANPR camera requires Day and Night (DN) lenses. These lenses are designed to maintain focus and image quality under changing lighting conditions. Since the vast majority of ANPR cameras employ IR light to avoid disturbing drivers during nighttime operations, using standard lenses can result in focus shifting at night. When the lens is focused properly in daylight, the use of IR illumination can cause focus shifts at night, leading to blurry plates. This focus shifting can significantly degrade the accuracy of license plate reading.
In conclusion, the success of ANPR software hinges on the selection of the proper ANPR camera. The distinction between ANPR cameras and standard IP cameras used for general surveillance is clear. ANPR cameras are purpose-built with global shutter sensors and optimized for capturing license plates accurately, even at high speeds. While it may be tempting to use standard IP cameras for ANPR applications, achieving highest accuracy in vehicle plate detection and reading is simply not possible with standard IP cameras. Therefore, when it comes to ANPR, it’s imperative to invest in the right camera to ensure the reliability and effectiveness of the ANPR software you have been using.