Figure 4. [color figure] Three typical scenarios on the observed light emanating from a point on the exterior surface of a transparent andrefractive object. The numbers in the figure indicate intensity magnitudes. (a) Nearly ideal specular reflection. In practice, the specularhighlight spans a finite region in the image. (b) Non-specular reflection where the intensity is similar to that of a true specular highlight.Examples include caustics and total internal reflection reflected off from the back surface of the object. (c) Non-specular reflection wherethe intensity is attenuated making it easily discarded by thresholding. Orientation consistency should be applied to (a), but not to (b) or (c)because they are not specular reflections.