Peter Nillius Jan-Olof Eklundh Phenomenological Eigenfunctions for Image Irradiance. 568-575 2003 conf/iccv/2003 ICCV http://csdl.computer.org/comp/proceedings/iccv/2003/1950/01/195010568abs.htm db/conf/iccv/iccv2003-1.html#NilliusE03