Vehicle License Plate Tilt Correction Based on Image Moments

The centroid and the normalized central moments of a vehicle license plate image are calculated，and the rotation angle α is obtained by minimizing the second order central moment based on its rotational invariance.Then whole image is rotated around the centroid by α to correct the image horizontal tilt. For the vertical tilt correction，two approaches，the one is based on the coordinate correlation coefficient， the other is based on line fitting with the least squares method，are proposed to compute the vertical tilt angle θ， and with which a shear transform is done on the previously rotated image for the final correction.The experimental results show that the proposed method is fairly reliable and accurate for the determination of tilt angles，and is a practical and effective tilt correction technique.