License Plate Recognition Algorithm And System Design

With the development of economy, the number of cars increased dramatically thus the Intelligent Transportation System(ITS) arises at the historic moment. License Plate Recognition(LPR) is an important part of ITS. The LPR System is a hotspot in Pattern Recognition research field and has good prospect and development potential.LPR System is combined by several parts such as image acquisition, image preprocessing, plate location,char split and char recognition. This paper studied the LPR in detail in plate location, char split and char recognition.The main content of the paper as follows:1,Introduced the application background, system configuration and current situation of the LPR System.2,Introduced several license plate image preprocessing methods such as color image graying and some image inhancement methods such as gray-scale transformation, histogram equalization and median filter.3,After the introduction of several edge detect algorithms, a plate location algorithm based on edge region connection was studied. This algorithm combines the edges of the image into some independent connected regions, then the areas which did not contain license plate were removed according to the geometrical characteristic between the licence plate and the background. Finally the position of the license plate was located accurately.4,After the location of license plate, it is necessary to rotate some license plates which were tilt. There are two kinds of tilt modes: one is horizontal tilt, the other one is vertical tilt. Methods based Hough transform and K-L expansion were used to correct horizontal tilt license plates and compare was did between these two methods. Then the vertical tilt licence plates were corrected by shear transformation. Then the frame of the license plate was removed. Finally the string on the plate was splited into single chars. After normalization and thining, these chars had the same size and the width of the strokes of the chars was one pixel.5,On the foundation of char spliting, coarse grid feature extraction was done on these chars. BP neural net was adopted to recognize these chars. According to the arrangement of the chars on the license plate, two classfiers one for Chinese chars and the other for combination of letters and numbers were used to recognize these chars. The recognition result was got after synthesizing the output of these two classfiers.6,Introduced the hardware platform TDSDM642EVM evaluation board which would be used to build the LPR system. CPU, memory, video ports,video codec and the ethernet were introduced. Coordinate with corresponding software and peripheral hardware, a LPR system could be built based on this board.7,Finally a LPR system was built on the VC++ platform by MFC tools. This system could recognize the license plates in the photos. The system menu and recognition procedure was shown in detail in the paper.