J. Ross Beveridge Bruce A. Draper Jen-Mei Chang Michael Kirby Holger Kley Chris Peterson Principal Angles Separate Subject Illumination Spaces in YDB and CMU-PIE. 351-363 2009 31 IEEE Trans. Pattern Anal. Mach. Intell. 2 http://doi.ieeecomputersociety.org/10.1109/TPAMI.2008.200 db/journals/pami/pami31.html#BeveridgeDCKKP09