Jeffrey Mark Siskind J. Sherman Ilya Pollak Mary P. Harper Charles A. Bouman Spatial Random Tree Grammars for Modeling Hierarchal Structure in Images with Regions of Arbitrary Shape. 1504-1519 2007 29 IEEE Trans. Pattern Anal. Mach. Intell. 9 http://doi.ieeecomputersociety.org/10.1109/TPAMI.2007.1169 db/journals/pami/pami29.html#SiskindSPHB07