Circular harmonic function (CHF) filters are used to determine the number of objects in a cluster in which multiple objects are touching and to provide estimates of the center of each object. The objects are agricultural products, pistachio nuts, and the sensor is X-ray. The nuts can have any orientation (hence rotation-invariance is necessary) . Each nut is basically elliptical, but shape, size and edge smoothness vary plus significant internal gray-scale variations are present; these variations are distortions. To detect such objects, we consider rotation-invariant RI-MINACE filters. To detect the separate correlation peaks, we use peaksorting with a window and minimum threshold. New filter design issues that arise in this application of rotation-invariant distortion-invariant touching object detection include: use of gray scale or binary images; the CHF order to use; selection of the reference object, the size of the filter, the MINACE control parameter c, and the size of the window and threshold in peaksorting.
Keywords: circular harmonic filters, detection, distortion-invariance, rotation-invariance, rotationinvariant MINACE filters.