True Dimensionality: BRDF example measured material properties (BRDFs) linear PCA: 25-45 dimensions needed interpolating gives impossible intermediate points: highlights with holes nonlinear charting: 10-15 dimensions needed physically plausible highlights [A Data-Driven Reflectance Model, SIGGRAPH 2003, W Matusik, H. Pfister M. Brand and L. McMillan, graphics.lcs.mit.edu/~wojciech/pubs/sig2003.pdf] 114