Research On License Plate Location And Char Segmentation Based On License Plate's Integrative Characteristics

Vehicle License Plate Recognition (VLPR) is an important application of digital image processing and pattern recognition in the transportation information system. With the fast development of transportation information system, VLPR has become an important research subject nowadays. In real conditions, a variety of causation would made License Plate Recognition more difficult, such as variety in illumination conditions, sloping license plate, the uncertainty of size and position of license plate in the captured image, the complex of image background, and etc. Current technique of License Plate Recognition is far away from perfect. Using new theory and new technology to reform license plate recognition technique is one of the research keys.License plate's location is the key of VLPR system. To find out a highly adaptive plate's location method, mathematical morphology close and open operation, image edge detect and color analysis based on HSV (Hue, Saturation, Value) model are researched and realized. And a series of key steps of plate's location are carefully analyzed and experimented with a mount of plate images too, including calculating dynamic size of the morphology template, validating effects of a variety of image edge detect operators, color distinguish method based on range threshold. Based on these work, a new plate location method using plate's texture, shape, color characteristics was proposed. The experimental results show that the method has strong adaptability to unconstrained illumination conditions and irregular background, and is efficient in locating license plate.The result of characters segmentation has remarkable effect on the choosing of the character recognition algorithm and the accuracy of character recognition. To reduced to the complexity of chars segmentation, paper brought forward a series of pretreatment methods to the retrieved plate, including using line imitate method and angle detect method to correct the plate's slope angle, using color projection method to eliminate conglutinative texture edge, and using bi-value image project method to eliminate plate's rivets and frame. The multiple pretreatments result in the favorable outcome, and provided the better preconditions for simple charactersrecognition method that based on template match. The VLPR location method proposed in this paper fully considers and utilizes the texture, shape and color features of VLPR in VLPR location, and has better adaptability than the method used before. The proposed multiple pretreatments method can effectively mend unfavorable VLPR, based on the mended VLPR, the final segmented characters has less distortion than coarse segmentation method, and can increase accuracy of characters recognition.