Perspective distortion exists on the car license plate photograph taken in a skew angle, under such situation direct rotation can't effectively rectify the distorted plate image, hence the distortion rectification procedure is required to precisely extract the plate character. 斜向拍摄的车牌图像存在着透视变形,该情况下直接进行车牌旋转不能有效地矫正,必须进行变形矫正才能准确地提取出各个牌照字符。
The method to estimate skew angle based on Radon transformation is very exact, and the distortion of corrected image is also very little; 基于Radon变换估计倾斜角度的方法检测角度精确,校正后图像失真较小;