I. Introduction
Plaster is a traditional Chinese medicine which is for outward application only. It belongs to the transdermal drug delivery system (TDDS) and is popular because of its unique treatment methods [1]. The quality of the plaster coating will influence the adhesion and use of the drug, so the quality of the coating determines the quality of the plaster. The current detection means for plaster coating is mainly artificial detection, which makes the process of detection is very subjective, some relatively small defects is not easy to be detected, and the artificial detection makes the work efficiency very low, and the plant environment is generally poor, which is not conducive to the health of workers [2]–[4]. Therefore, it is necessary to design a set of automatic quality inspection system for plaster coating.