Patent ID: 6356300
Filing Date: 2002-03-12
Classification: G01N,G03F,G06T

Abstract:
An automatic visual inspection apparatus comprising:an image division differential unit having inputs of an inspection image on the object to be inspected and a reference image for making comparison with the inspection image, for spatially differentiating the respective inputted images and dividing them into the predetermined number of divisions to form the divisional differential images; a pixel precision position alignment unit overlaying the inspection image and the reference image by carrying out the position alignment in pixel precision which is a pixel size precision between the inspection image and the reference image on each of the divisional differential image formed by said image division differential unit; a function fitting unit which regards the point where the absolute pixel value is larger than the predetermined threshold value to be an edge in each divisional differential image, obtaining the direction of the edge, obtaining the intensity profile of the absolute pixel value in the direction orthogonal with the edge, fitting a predetermined single peak function to it, obtaining the maximum value point which is a coordinate of the point where its function takes the maximum value by a sub-pixel precision which is the precision lower than the pixel size, and employing the resulting value as coordinate of an edge; a sub-pixel precision position displacement computing unit which functions so that, if, after the laying over of the images together in the pixel precision position aligning unit, there is an edge in the region on the reference image corresponding to the neighborhood of the edge, these two edges are regarded as being in the corresponding relations, and computing the difference of the mutual edge positions as a position displacement of the sub-pixel precision; an adjusted differential image forming unit for forming the adjusted differential image by rewriting the pixel value so that the intensity profile of the pixel value in the direction orthogonal with the edge should follow the previously given single peak type function form on the corresponding two edges; and an image comparison unit for detecting the defect of the object to be inspected by comparing the adjusted divisional differential image of the inspected image with the adjusted divisional differential image of the reference image based on the position displacement of the sub-pixel precision of each divisional differential image computed by the sub-pixel precision position displacement computing unit.