Car License Plate Recognition Technology Research

Automatic License Plate Recognition System is a specific computer vision system based on the specific goals of the vehicle license. A typical License Plate Recognition System is composed of License Plate Detection, Plate Character Segmentation and Character Recognition. The LPR system involves numerous discipline domains, such as Pattern Recognition and Artificial Intelligence, Computer Vision, Digital Image Processing, Artificial Neural Network etc.The purpose of the paper is analyzed as follows. The image inputted to the computer is disposed and analyzed in order to recognize the characters on the license plate and complete the character segmentation and recognition. At last the vehicle license plate number is printed in text string according to the order of original images, and sent to the database. Based on the research of key technologies in LPR, a tentative LPR system is set up.Locate the plate is the first step of the LPR system, whose accuracy directly affects the success of the character recognition result. Firstly, image pretreatment is processed. Secondly, row-scanning is adopted as the horizontal location method. Then, vertical projection is adopted to determine the left and right boundary of the plate. The result proved that, it can satisfy the demand in accuracy.The result of character segmentation affects the recognition directly. Before character segmentation, line-scanning method is taken to determine the horizontal gradient of the top and bottom of character grain area. According to the angle, incline-revising is adopted, and at the same time remaining frame and rivets are also wiped off. Then, vertical projection is adopted to determine the left and right boundary of every character and segment the characters. After that, normalization is taken.Character Recognition takes the most important part in the whole system, which is the purpose of the system design. According to the feature of characters on the plate, BP Artificial Neural Network is adopted as a classified recognition method. Single normalized character is delivered to Chinese character recognition sub-network, letter character recognition sub-network, letter and number recognition sub-network, and number recognition sub-network separately. Finally, the results are printed in text strings according to the order of original images, and sent to the database.Experiment results show that, the LPR system discussed in the paper can accurately locate to license plate, segment and recognize characters. And the system's performance is good.