Abstract: The “W” pattern target is a kind of four-wheel alignment’s calibration target.It is very important to search the right contour in a positioning image quickly.The Hu moment and the pair-wise geometric histograms algorithm are traditional methods,and they are low in speed and poor in robustness.Some Fourier descriptor for trademark image retrieval can be well applied to quick contour matching.But searching a target contour in an image may introduce too much interference of many contours.In this paper,we used the Fourier transform to extract the contour’s spectrum characteristics,then measured the similarity by examining the disruptive of target contour to the template contour,and simplified the algorithm to achieve the goal of fast matching.Its anti-interference ability is strong,and searching efficiency is high.This suggests that the method of Fourier transform of edge curve to match contour has good applicability.

Key words: Image,Fourier descriptor,Contour matching