| The techniques of Car License Plate Recognition is used widely in the ITS field recently.There are some problems still existed in the current working system:the performance of system is not stable enough; the remedy method of distorted image is not adopted in the case of vertical incline grade is large; the recognition rate of character classifier is not high enough to meet the need and the training period of character classifier is too long . All of these need the researchers to better the algorithms and optimize the system.An whole Car License Plate Recognition System consists of three components: image inputting^icense retrieving^character recognition. This thesis focuses on the software part of the system including "license retrieving" , " character recognition" .In order to solve the problems described above, some deep researches including the algorithm of the computing of incline grade of license plate, the remedy method in the case of vertical incline grade is large, the exact plate retrieving algorithm, the character recognition method, and the combination method of multi-classifiers, have been carried out in this thesis.Main research work of this thesis includes:Canny arithmetic operator of edge detection is introduced firstly in the algorithm of the computing of incline grade of license plate. The experiment result proves the performance of Canny operator is more excellent than the traditional operator such as Sobel.A "simple space-transformation" method is proposed to remedy the image distortion in the case of vertical incline grade is large whereas nothing is done in the case of vertical incline grade is small in this thesis. This purpose of novel method of discriminated treatment is to improve the recognition rate, and reduce the zigzag occurrence of characters.Two universal methods of exact plate retrieving are presented. One is exact plate retrieving method based on corner detection. The otheris exact plate retrieving method based on line edge inspecting. And a new method is proposed here based on the geometry. According to the transformation rules of the geometry coordinates before and after the image rotation and the estimated computation of the coordination of the plate center, a formula could be deduced , and the four corners are marked. Compared with the two universal methods , the geometry-based method has a shorter computing-time consumption, and a stronger ability of anti-incline of plate.In the stage of character recognition , a lot of methods are presented in this thesis, including the structure recognition method , the statistical recognition method, the structure and statistical combination recognition method, and artificial neural network classifier recognition method. Hidden Markov Module and its application in character recognition are presented in brief. It is proved here that the method of combination of multi-classifiers with the confidence computing could improve the recognition rate via an alphabet and digits recognition classifier module scheme experiment.Some researches and discussion have been carried out on the application of Statistical Learning Theory and Support Vector Machine in character recognition. SLT and SVM are the new hotspots in machine learning field. SVM represents better performance than most other machine learning method because of the requirement for limited number training samples, different kernel function could deduce the approximate recognition result, shorter training-period interval, higher recognition rate .On the one hand the "SeeCar" system have adopted many known excellent methods cited from the domestic and international published paper, on the other hand some new algorithm with better performance have been put up . The stability of system has been emphasized during the whole developing period .The next step work will be carried out in the future including the following aspects: A SVM-based character classifier will be introduced in the recognition module with the aim to ehance the whole recognitionrate; A pre-...
|
PDF Full Text Request