The Research On Key Techniques Of License Plate Recognition System

As an important part of intelligent transportation systems, the license plate recognition system has an important role in violation enforcement, parking management, intelligent traffic management and the important points of vehicle registration. From the view of practical application, some researches have been done on license plate location, license plate segmentation and character recognition against the outdoor background of urban roads and highways. The main work is as follows:On the basis of studying the existing vehicle license plate location algorithms, An License plate location based on edge detection and mathematical morphology has been presented.The Sobel edge detection has been improved, by setting the threshold to reduce the small edges’disturbance around the background, through using connected domain analyses based on morphological processing to complete the license plate location.In terms of character segmentation, first, a tilt correction of license plate based on least squares and minimum projection distance has been put forwarded, on level correction, using least square to fit a straight line for obtaining the slope angle, on vertical correction, using an improved minimum projection distance method, it has reduced the number of execution and improved the execution efficiency. To the licenses which have been corrected has been segmented using modified projection method. Also the characters which are adhesion and fragmentation have been given special treatment.In terms of extraction, a feature extraction based on Wavelet transform and Zernike has been presented.wavelet transform has extract the details of character features, Zernike moments has extract the global character features, the combination of those has distincted the character between each other. And using principal component analysis to reduce some features which have large correlation with others, the number of the operation of algorithm also has been reduced.Last, based on the analysis of the neural networks and support vector machine(SVM), using SVM to design the network of license plate characters, it has not only high recognition rate, small measurement error, but also a strong generalization.Finally, on the Matlab simulation platform, a large number of plate images has been tested. Results show that the improvement algorithms have high effectiveness and the value of practical application.