Recognition of Motor Vehicle License Plates in Rear-View Images

Abstract

In this paper a system for the recognition of car license plates is presented. The aim of the system is to read automatically the Italian license number of a car passing through a toll-gate. A TV camera and a frame grabber card are used to acquire a rear-view image of the vehicle. First, a segmentation phase locates the license plate within the image. Then a procedure based on feature projection estimates some image parameters needed to normalize, by a bilinear resampling, the license plate characters. Finally, the character recognition extracts the desired information. Feature points and template matching operators are used to get a robust solution under multiple acquisition condition. The system is able to reject an image if some conditions are not met, as, for instance, the passage of a foreign car through the tollgate. A test has been done on more than three thousand real images acquired under different weather and illumination conditions. Within a test set the system has discarded all the unrecognizable images, i.e., not provided with the required characteristics. The recognition rate has been close to 91%. The final percentage may increase if a more accurate drawing of the templates is performed.