Dynamic Vision for License Plate Recognition

The problems related to license plate recognition and management are much more complex than simple character reading of the car-plate on a sharply illuminated, well contrasted, in-focus, still image of a car (front or rear views). There are many system-engineering issues to be addressed when dealing with license plate recognition and tracking. Image acquisition is the first fundamental step of the process, quite critical in such an almost unconstrained environment like outdoor scenes. It requires multidisciplinary competence of electro-optics, and installation constraints. Infrared lighting is widely used especially at night, which minimizes external uncontrolled conditions. The position of the sensor and its orientation are other essential issues, to minimize perspective deformations of the characters and achieve the necessary resolution in the scene. In general, whatever kind of camera is used, it should be placed to avoid occlusion of the license plate, and allow the acquisition of the plate field as much as squared as possible. Angled views of up to 30°, in the horizontal or vertical plane are usually manageable. It is good practice to ensure that the license-plate characters appear as near vertical as possible in the digitized image.