A method of slant correction of vehicle license plate based on watershed algorithm

In a vehicle license plate recognition system, slant vehicle license plate has a bad effect on the character segmentation and recognition. A method of slant correction of vehicle license plate is proposed in this paper. The method consists of five main stages: (1) the extraction of the boundaries of characters using watershed algorithm; (2) dividing the boundaries of vehicle license plate into small segments using vertical differential method; (3) connection of the fracture characters using expansion and corrosion; (4) computing centroids of the left and the right part in the vehicle license plate respectively; (5) finding the slant angle by means of two centroids. Experimental results show that the error rate of using the method is 6.13%, which is lower than that of the principal component analysis. The running time of using this method is less than that of Hough transform. The method improves accuracy of the slant correction.