Abstract
Why do we see the surface of a polished car as a specular reflection of the surrounding environment rather than as a texture property of the car itself? In addition to highlights, other surface properties might contribute to perceived specularity. This study explores whether deformations of the reflected scene and the nature of the scene itself contribute to perceived specularity. Human observers viewed pairs of images of mirrored surfaces reflecting different surrounding environments and judged which image was more specular. We used a CAD package to render images of mirror-like objects reflecting a range of surrounding scenes. The objects were composed of shape primitives and the scenes were either real-world or synthetic environments (e.g., ellipses on the hemisphere). Surprisingly, objects reflecting artificial environments produced a much weaker impression of specularity than did those reflecting natural environments - reflected synthetic environments were more likely to be seen as the surface texture. Critically, the nature and magnitude of the deformation of the reflected environment was virtually identical across synthetic and natural scenes. Additional experiments showed that the phase component of the spectral decomposition of the scene plays an important role: reflections of a phase-randomized scene (using an algorithm based on RISE) weakened perceived specularity. Phase randomization weakens the spatial structure of scene, further suggesting that deformation cues based on reflected scene structure affect specularity perception. Yet reflections of phase randomized scenes were still seen as more specular than reflections of synthetic environments. All this suggests that the perception of specularity is strongly affected by the statistics of the surrounding environment - natural statistics yield a stronger impression of specularity. Thus, deformations acting on the reflected scene appear to be a necessary but not sufficient cue.