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Real-Time Inverse Lighting for Augmented Reality Using a Dodecahedral Marker

Straughn, Glen Kemp
Lighting is a major factor in the perceived realism of virtual objects, and thus lighting virtual objects so that they appear to be illuminated by real-world light sources - a process known as inverse lighting - is a crucial component to creating realistic augmented reality images. This work presents a new, real-time inverse lighting method that samples the light reflected off of a regular, twelve-sided (dodecahedral), 3D object to estimate the light direction of a scene's primary light source. Using the light sample results, each visible face of the dodecahedron is determined to either be in light or in shadow. One or more light vectors then are calculated for each face by either using the surface normal vector of the face as a light direction vector if the face is in light, or by reflecting the face's surface normal across the normal vector of every adjacent illuminated face in the case of shadowed faces. If the shadowed face is not adjacent to any illuminated faces, the normal vector is reversed instead. These light vectors then are averaged to produce a vector pointing to the primary light source in the environment. This method is designed with special consideration to ease of use for the user, requiring no configuration stages.