Real-time automated visual inspection of color tablets in pharmaceutical blisters

In pharmaceutical blister packing, it is today part of the recommended security standard to inspect tablets in each blister before it is sealed: In this paper an automated visual inspection system is described, which detects missing and broken tablets, tablet fragments, as well as the color, size, and shape of individual tablets. The system operates either in "training" or "inspection" mode. In training mode, the image of defect-free blisters is used to extract the blister model, which is composed of the spatial color nonuniformity correction function, positions of blisters, positions of tablets in blisters, the color labeling function, and position, size, and shape of each tablet and corresponding pre-specified tolerances. The blister model allows effective and real-time analysis of blisters in inspection mode. The most important parts of the system are correction of the adverse effects of spatial color nonuniformity and color segmentation. A method recently proposed for spatial intensity nonuniformity correction has been extended to suppress spatial color nonuniformity in color images. A novel nonparametric clustering-based segmentation method is proposed, which finds the valleys between color clusters. The experimental results indicate that the segmentation method preceded by spatial color nonuniformity correction accurately extracts color clusters with complex shapes and therefore correctly segments the inspected images. The automated visual inspection system can thus be used in industrial environments where real-time inspection of color objects is required.