Vehicle License Plate tilt correction based on the Weighted Least Square Method

Tilt correction is a very crucial part of the Vehicle License Plate (VLP) automatic recognition. In this paper, according to the Weighted Least Square Method (WLSM), the VLP region is fitted to a straight line and then the line slope a₁ is obtained, by which the rotation angle a α is calculated. Finally the whole image is rotated by -α and the image tilt correction is performed. The experimental results definitely show that, this paper method can quickly and accurately get the tilt angle and has great robustness and adaptability. Compared with the Least Square Method (LSM), in this paper method the tilt angle is more precise and the value of objection function is smaller; Compared with Hough Transformation (HT) and Radom Transformation (RT), this paper method is featured in faster processing time and more precise tilt angle, which is particularly well adapted to the real-time tilt correction in Intelligent Transportation System (ITS).