关键词: 机器视觉, 图像处理, 亚像素边缘, 聚类分析

Abstract: To promise stress-free and precise assembly for bend tubes,the geometric parameters shoule be measured during the manufacturing stage.Machine vision based measurement for bend tube is a rapid and accurate method,which is widely used in the field of 3D measurement.Aiming at the problem that the traditional extraction in this method could not obtain pipeline edge accurately,a sub-pixel edge extraction method for tube's image even was proposed under a complex illumination condition.The extraction was explained in four steps: the low-frequency noises were filtered with spectral filtering method,and  a clustering analysis method was applied to segment the tube's region precisely;the pixel edge was obtained with image morphology method.The surface fitting method was employed to fitting the variation of local gray values to realize the sub-pixel edge points.Experiments results showed that the method could extract sub-pixel edge accurately and reliably.The accuracy reached 0.04 pixel width,which could provide the accurate edge for reconstructing tube's 3D model.

Key words: machine vision, image processing, sub-pixel edge, cluster analysis