Takahiro Okabe Imari Sato Yoichi Sato Spherical Harmonics vs. Haar Wavelets: Basis for Recovering Illumination from Cast Shadows. 50-57 2004 CVPR (1) http://csdl.computer.org/comp/proceedings/cvpr/2004/2158/01/215810050abs.htm db/conf/cvpr/cvpr2004-1.html#OkabeSS04