Tuesday, March 18, 2008

Skin Reflectance

Paul Debevec, Tim Hawkins,Chris Tchou, Haarm-Pieter Duiker,Westley Sarokin and Mark Sagar. (2000). Acquiring the reflectance field of a human face. Proc. ACM SIGGRAPH, 145–156.

Weyrich, T., Matusik, W., Pfister, H., Bickel, B., Donner, C., Tu, C., McAndless, J., Lee, J., Ngan, A., Jensen, H. W., and Gross, M. (2006). Analysis of human faces using a measurement-based skin reflectance model. Proc. ACM SIGGRAPH, 1013-1024. See the very cool presentation and demo (with matching video) of nvidia's human head, focusing primarily on skin.


Unknown said...

What are the limitations of their Light Stage? Many other capture methods (including the one use by Weta for LoTR which I've actually tried) are much more apt to failure for "reflective" faces, like if someone has oily skin. Their models appear to have very matte skin, was there some sort of preparation that was needed before the capture (Light Stage or real-world+light probe) was taken?

Speaking of the light probe, I'm not sure I really understand how this works. How does the light a small, perfect sphere observes relate to an inhomogeneous, much larger object like a human head? Fig. 15 doesn't provide much illumination (pun intended!) as to what's going on because the differences between photo and render are little to none.

Another oddity with Fig. 15: in (e) the lady seems to have a black spot on her nose that doesn't appear in the composite (g). What's going on there?

The translucency measuring system here is interesting to me. Other than reliability, why choose the cheek, forehead, and under-chin? Why do you even need the three measurements; how does facial skin vary over one's face? What if the person is "unmeasurable" on the cheek or chin (say if they have facial hair in one or both)?

Why does less translucency result in sharper shadows (Fig 12)?