PT Journal
AU Fyffe, G
   Debevec, P
TI Cosine Lobe Based Relighting from Gradient Illumination Photographs
SO JVRB - Journal of Virtual Reality and Broadcasting
PY 2012
VL 9(2012)
IS 2
DI 10.20385/1860-2037/9.2012.2
DE Gradient Illumination; Lighting; Photographs; Relighting; Scene Geometry; Shadows
AB We present an image-based method for relighting a scene by analytically fitting cosine lobes to the reflectance function at each pixel, based on gradient illumination photographs. Realistic relighting results for many materials are obtained using a single per-pixel cosine lobe obtained from just two color photographs: one under uniform white illumination and the other under colored gradient illumination. For materials with wavelength-dependent scattering, a better fit can be obtained using independent cosine lobes for the red, green, and blue channels, obtained from three achromatic gradient illumination conditions instead of the coloredgradient condition. We explore two cosine lobe reflectance functions, both of which allow an analytic fit to thegradient conditions. One is non-zero over half the sphere of lighting directions, which works well for diffuse and specular materials, but fails for materials with broader scattering such as fur. The other is non-zero everywhere, which works well for broadly scattering materials and still produces visually plausible results for diffuse and specular materials. We also perform an approximate diffuse/specular separation of the reflectance, and estimate scene geometry from the recovered photometric normals to produce hard shadows cast by the geometry, while still reconstructing the input photographs exactly.
ER