Study of Measurement Method in Inter-Vehicle Distance Using Hu Moment Invariants

This paper proposed a method to detect the license plate by using the Hu moment invariants and measure inter-vehicle distance. The method was aimed at practical driving-support system with single image sensor. Adaptive thresholding process made the detection robust against changes of brightness caused by weather changes, which have been a major problem of image processing in outdoor. Adaptive thresholding process achieved the detection rate of 93.2% This result shows that the robustness of the system has been improved. At a distance of 2 to 15 m, the error rate was about 4 to 6 %and the average absolute error rate was 4.75 % The average time for all processes was 44.67 ms, which shows that this method operates at a maximum speed of about 22.39 fps.