Find Straight Edge Concepts

The Find Straight Edge step searches for a straight edge in a two-dimensional region of interest. The region of interest contains a number of search lines along which the step searches for sharp transitions in pixel intensities. A sharp transition typically characterizes the edge of an object in the image. The step fits a straight line through the individual edge points of each search line to determine a straight edge on the object under inspection.

The step locates an edge based on its edge strength. You can study the Edge Strength Profile to determine the edge strengths for each search line in the region of interest. A peak in the profile indicates that an edge is present at that position in the region of interest. The strength of that edge is given by the amplitude of the peak.

The default region of interest tool is a rectangle. If the edge you want to locate is at an angle in the image, use the rotated rectangle tool to draw the region of interest. If the edge extends radially from a center point, use the annulus tool to draw the region.

Draw the region of interest so that it encloses the entire edge that you want to find but excludes as many edges of no interest as possible. Make sure the edge fills up most of the region length. Also, make sure that the region is at least 20 pixels wide on either side of the edge to accurately detect the points along the edge.