Athinodoros S. Georghiades David J. Kriegman Peter N. Belhumeur Illumination Cones for Recognition under Variable Lighting: Faces. 52-59 1998 conf/cvpr/1998 CVPR http://dlib2.computer.org/conferen/cvpr/8497/pdf/84970052.pdf db/conf/cvpr/cvpr1998.html#GeorghiadesKB98