Abstract: In the extraction of the edge of the housing,usually due to the segmentation of the region is not accurate,resulting in the extraction of the outline appear irregularities such as concave or convex parts,which needs to further fitting.Corner detection plays an important role in contour shape extraction.The traditional corner detection is based on the calculation of the maximum curvature point.This calculation method is completely dependent on the curvature variation of the profile,and can not be used for the repair of its irregularities.So it’s difficult in removing some of useless corner points.In this paper,a new method based on the minimum external rectangle to fit its real shape was proposed.In detail,the minimum external rectangle is used as the outline,and the difference between the fitted contour and the outer rectangle is calculated.It sets the appropriate threshold value for the difference,then chooses the right point for the polygon according the threshold.Without needing to calculate the corner points by the curvature of the contour,we can get the right-angled polygon of the object contour,which is simple and efficient.

Key words: Transformation of coordinate system,Corner point,Difference between inner and outer contour,Polygon fitting