The Research Of Vehicle License Plate Locating System

The vehicle license plate automatic recognition system is one of the important research subjects in the traffic department.The complete vehicle images are sampled from CCD video camera for our system as well as for monitoring. We assume camera is installed a fixed position and vehicle pass it from the same direction , the same angle and the same position .To segment a vehicle license card from the image background of the whole vehicle , a image segmentation algorithm basing on cross variance and Mathematical morphology is presented. In the plate region of a vehicle image , the gray value varies frequently in cross-direction , so We define a parameter ".cross variance" to describe it .We also calculate other parameters to approximately locate the plate , they are the space length between two chars ,the thickness of stroke , the peak and trough of gray value , the ratio of width and length , etc. At last , We exactly locate the plate by the theory of Mathematical morphology.More than 1 thousand image samples are selected from those acquired from a highway tollgate . The samples almost include all kinds of vehicle plates under using in China now and the conditions of different weather and illumination . To the 1 thousand images , the locating rate is close to 95% and the locating holds about half second.