Jonathan Shade Dani Lischinski David Salesin Tony DeRose John M. Snyder Hierarchical Image Caching for Accelerated Walkthroughs of Complex Environments. 75-82 1996 SIGGRAPH http://doi.acm.org/10.1145/237170.237209 db/conf/siggraph/siggraph1996.html#ShadeLSDS96