An Efficient Method for Skew Correction of License Plate

Character segmentation and recognition are important steps in the automatic license plate recognition (ALPR) system. The skew license plate has a great influence on the accurate character segmentation and recognition. To solve the problem, an efficient approach for skew correction of license plate is proposed. First, the plate image is divided into a set of 5×5 non-overlapping blocks. The local orientation of each black is estimated by gradients of pixels in the block. The horizontal incline angle of license plate is detected by the local maximum of the direction angle histogram. The plate image is rotated according to this angle. Then, the vertical distortion of license plate image was corrected by the single-character projection method. The experimental results demonstrate the great robustness and efficiency of proposed method.