Spherical Harmonic Illumination 2013 (1) Borom Tunwattanapong, Graham Fyffe, Paul Graham, Jay Busch, Xueming Yu, Abhijeet Ghosh, Paul Debevec, Acquiring Reflectance and Shape from Continuous Spherical Harmonic Illumination, ACM Trans. Graph., volume 32, pp.109:1–109:12, 2013