Anat Levin Alex Rav-Acha Dani Lischinski Spectral Matting. 1699-1712 2008 30 IEEE Trans. Pattern Anal. Mach. Intell. 10 http://doi.ieeecomputersociety.org/10.1109/TPAMI.2008.168 db/journals/pami/pami30.html#LevinRL08