Viewing zone of aerial hollow face illusion evoked by use a 3D object as a light source for AIRR optical system

An aerial 3D image formed by the use of a 3D-shaped light source gives a greater sense of reality compared to the conventional aerial 2D image. In particular, an aerial image of hollow face evokes a kind of illusion that the direction of the face changes depending on the viewing direction. In this study, we investigate the viewing zone of an aerial 3D display that employs a 3D object as a light source in aerial imaging by retro-reflection (AIRR) optical system. The viewing zone is defined by the minimum observation distance and viewing angle where the entire width of the aerial 3D image is visible. The Formulae for the viewing zone are derived and confirmed experimentally. 3D objects in various shapes are used in the experiments. The aerial 3D image of each object was observed in the corresponding viewing zone. Hollow face illusion was evoked even under binocular observation. We have clarified the optical design of our proposed AIRR optical system for hollow face illusion.