Spatial Correction of the Distorted License Plate Image of Automobiles

According to the general style of automobile license plates in China, a method based on Hough transformation is proposed to acquire the parameters of four borders of the license plates. The coordinates of the four vertices of the quadrilateral plate are obtained, and away to performHough transformation for lines in the polar coordinate system is also presented in detail. Then, the bilinear spatial transformation equations are solved according to the mapping between the four vertices of a distorted plate image and its normalized vertices, so as to correct the distorted plate image. Finally some smoothing procedures are used to erase the burrs of characters in the plate image. Experimentresults showthatwiththe method introduced in this paper the distorted license plate images can be well normalized.