Shadow Access to Tabletop Information Optically Hided by Polarized Complementary Image Projection
We propose the concept and implementation of a graphical information hiding technique for interactive tabletops where users can view the information by simply casting real shadows. We placed three projectors (one in the rear and two in the front) in such a way that the rear one projects graphical information onto a tabletop surface, and the front ones project a complementary image, so that the combined image displayed on the surface becomes uniformly gray, thus hiding the information from the viewer. Users can view the hidden information by blocking the light from the front projector, revealing the complementary image that is being projected onto the occluder. We use the other front projector and polarization filters to make the complementary image projected onto the occluder also uniformly gray. Because the technique completely relies on optical phenomena, users can interact with the system without suffering from any false recognitions or delays.