Research Of Restoration, Location And Calibration Of Motion-blurred License Plate Images

The License Plate Recognition (LPR) system becomes an important part of Intelligent Traffic System(ITS) with the rapid development of computer science and digital image processing.The essential technology of the recognition of the motion-blurred images of vehicle's license plate system lies in the digital image pretreatment technology, the plate location technology and the intelligent character recognition technology. The paper applies the identification of motion blur direction and the blur extent, the license location technology, the character division technology, the license character recognition technology based on BP networks to the LPR system. By considering the processes of the vehicle's license plate identification, screening methods and algorithms according to the demands of each link function, the paper makes a comparative analysis of the key links and algorithms by experiments, and the related algorithms are improved or some new algorithms were put forward.Firstly, improve the identify approach for motion-blur parameters (motion-blur direction and motion-blur extent)from motion-blurred image based on directional derivation and autocorrelation method, put forward a optimized algorithm to search the extremum, which makes the solution fast.Secondly, approved the license plate location algorithm based on the characteristic of license plate's gray-scale. Extend the width of the segmentation area and synthesize other methods such as hough transfer to screen the candidate regions to make it successful in handling the declining images or images with complicated background.Thirdly, Study the image calibration based on homography matrix method. The key of this method is to detect edges and their intersections. A new automatic edge detection method was put forward to the calibration of license plates. This method obtains the edges of pictures and their intersections through merging, sorting and ranging based on hough transformation automatically. For the problems result from different proportions of length and width, this paper also gave an analysis and made relative processing. Simulation result shows that this method has good performance as well as preserving the convenience of homography matrix calibration.At last, to the problem of character division, an edge rejecting algorithm was put forward. This algorithm can reject the edges of vehicle's license plate efficiently, which is very convenient for the following treatments.