中文摘要：

提出了三点平均平滑曲线的方法。用灰度直方图的缩小曲线来辨别白天和夜晚的车牌图像，用纵向差分、二值化、纵向投影、三点平均平滑、曲线放大等方法突出车身的横直线，查找车身左右边界，排除地面背景和缩小车牌搜索范围．由此设计了一个应用于高速公路超速监控的车牌识别系统。

英文摘要：

The method of three-point average smooth carve is proposed in this paper. The shrinked curve of grey histogram is used to distinguish the licence images at day and night. And with the methods of vertical difference, binaryzation, vertical projection, three-point average and curve magnification ,the horizontal lines of vehicle body is extruded ,the left and right borders of the vehicle body are searched , the floor background is excluded,and searching area of the licence is reduced. And thus, the licence recognition system is designed and applied to the overspeed supervision in freeway.