Model based visual inspection of pharmaceutical tablets with photometric stereo

A model based visual inspection of pharmaceutical tablets is proposed for the detection of surface defects that occur during the tableting process. A novel RB-BR photometric stereo configuration is used to obtain four images for every tablet at different lighting orientations. During the inspection, reconstructed 3D depth maps derived from acquired images are compared to the tablet model, obtained during the training phase. Inspected tablets are classified as defective if the difference exceeds a predefined threshold. The approach was tested on two sets of tablets and compared to the current state of the art methods. The results yield 89 % and 87 % successful defect detection rate for tablets without and with embossing, respectively.