Simulation of an inverse schlieren image acquisition system for inspecting transparent objects

This paper describes a novel approach for inspecting transparent objects. Since the underlying optical setup is based on a schlieren setup, any defect can be detected that leads to the deflection or extinction of incident light rays. By capturing a light field image of a defect-free transparent object and by illuminating objects under test with that very light field, the proposed inspection system can visualize defects by acquiring a single inspection image only. In order to evaluate the presented approach, a physically based rendering framework is used. It is extended by models and implementations of the necessary emitter and sensor plugins. Simulation experiments with virtual scenes that consist of a double-convex lens affected by different types of defects are the basis for a qualitative evaluation of the proposed method. The results show that a single image acquired with the described method is sufficient to test transparent objects for defects that cause the deflection or extinction of rays, e.g., enclosed absorbing or scattering impurities, shape anomalies, differences of the index of refraction and 3D-misalignments.