Radial histograms as an aid in the inspection of circular objects

This paper considers the inspection of circular objects. Template matching forms a competitive approach for inspecting these products, but radial histograms are found to be especially useful whenever products are nearly symmetric. Various methods of renormalising radial histograms are compared, with particular reference to accuracy and resolution. It is shown that radial histogramming is valuable for checking quickly for various defects, and that it can lead to increased accuracy of radial measurement. Its capabilities depend strongly on the previous accurate location of the centres of circular regions: the Hough transform approach is well adapted to this purpose.