About the acquisition and processing of ray deflection histograms for transparent object inspection

Objects made from transparent materials are of great importance in our every-day life. In order to work as intended, these objects have to meet high quality criteria. Since their transparency makes many existing machine vision methods for opaque objects inapplicable, novel approaches have to be found. This paper proposes an optical inspection system based on a 4f light field camera in concert with parallel illumination, so that local histograms of the deflections of light rays exiting the test object can be acquired. Furthermore, the article presents two different approaches for processing these histograms of ray deflections (HORDs) in order to visualize scattering defects present in the test object. To evaluate the suitability of the proposed acquisition setup and the light field processing methods for the visualization of scattering material defects, different experiments are performed using a physically based rendering framework.