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Curvature-Based Shading of Translucent Materials, such as Human Skin

Curvature-Based Shading of Translucent Materials, such as Human Skin . Konstantin Kolchin DMP Inc. Introduction and Previous Work. Subsurface scattering in translucent materials transfers light away from the entrance point. The result depends on local geometry.

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Curvature-Based Shading of Translucent Materials, such as Human Skin

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  1. Curvature-Based Shading of Translucent Materials, such as Human Skin Konstantin Kolchin DMP Inc.

  2. Introduction and Previous Work • Subsurface scattering in translucent materials transfers light away from the entrance point. The result depends on local geometry. • To describe this, Nicodemus et al. 1977 introduced Bidirectional Surface Scattering Distribution Function (BSSRDF).

  3. Introduction and Previous Work, cont. • Jensen et al. 2001. Dipole-source model for BSSRDF. • Jensen and Buhler 2002. Hierarchical rendering with the dipole-model BSSRDF. • Borshukov and Lewis 2003. Texture-space diffusion. • Dachsbacher and Stamminger 2003. Translucent shadow maps. • Mertens et al. 2005. Importance sampling of BSSRDF in screen plane.

  4. Introduction and Previous Work, cont. • d'Eon and Luebke 2007. Texture-space diffusion extended with stretch correction.

  5. Diffusion approximation • The integral is four-dimensional. To render subsurface scattering in real time, one have to calculate this integral in real time.

  6. Notation

  7. Scattering neighborhood factor • Similarly to Hao and Varshney 2004, we integrate first over surface and then over directions. The surface integral is called the scattering neighborhood factor(SNF), p, so that

  8. Integration of SNF using Monge’s form • Our suggestion is to compute SNF using Monge’s form. • Any smooth surface can be locally represented in Monge’s form or, with axes taken along the principal curvature directions,

  9. Integration of SNF using Monge’s form, cont. • Expression for SNF,, becomes where is defined by and

  10. Possible simplificationsExample 1 • One of possible simplifications is to replace Ft with its average value. SNF is then expressed in terms of a simple integral that can be precalculated.

  11. Possible simplificationsExample 1, cont.

  12. Possible simplificationsExample 2 • Another approximation is • to set curvature to constant • to neglect tangential dependence Geometrically, this means to locally replace the object surface with a paraboloid.

  13. Possible simplifications Example 2, cont. b a c d a – ‘true’ curvatures, b,c,d – constant curvature (2 times difference)

  14. Summary We suggest a new method for shading 3D objects with translucent appearance. It can be used for real-time rendering.

  15. Future work To generalize the method to higher-order surface derivatives. To adapt it to low-frequency illumination (using spherical harmonics). To solve the problem for simple shapes, such as a sphere or cylinder.

  16. That’s all • Thank you for your attention

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