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  • Subsurface scattering in point-based rendering

Photonics Spectra
Feb 2011
SEOUL, South Korea – The point-based graphics method of surface rendering has been touted as an alternative to polygon-based graphic methods because of its simplicity and flexibility. But point-based techniques have not offered sufficient rendering quality when it comes to translucent materials such as human skin – until now.

A new framework from the department of computer engineering at Sejong University and ETH Zurich in Switzerland enables realistic rendering of subsurface scattering in such materials.

A novel approach to point-based rendering allows the method to be used for translucent materials such as human skin.

Point-based rendering is typically a three-pass process, so to simulate subsurface scattering in multilayered materials, the engineers added two new computation passes: shadow map generation and splat-based diffusion. The latter uses splats to approximate the light diffusion phenomenon inside a material; the assumption is that the diffusion of light is isotropic, so its effect can be expressed as a Gaussian distribution applied to the radius of the splat. The overall diffusion effect across the surface is determined by combining the contribution of all the splats.

As the splat’s radius increases in the surface splatting, the process slows down because of an increase in the number of fragments projected on the screen space. Although the number of splats with large radii decreases, the large overlapping area between splats means that the outcome does not change very much, enabling a reduction of the number of splats when the amplitude of the radius is large.

“Although in this paper we apply the surface splatting with subsurface scattering to human facial skin, our method can be used for various translucent objects such as marble, leaves and milk by analyzing the scattering of laser or structured light patterns,” said Soo-Mi Choi, a co-author of the paper. “In the future, we plan to optimize the number of splats required to produce each diffuse color image and to adjust the resolution using perception-based metrics.”

Choi and colleagues published their results in the November 2010 article “Subsurface scattering using splat-based diffusion in point-based rendering,” Vol. 53, No. 5, of Science China Information Sciences.

light diffusion
The scattering of light by reflection or transmission. Diffuse reflection results when light strikes an irregular surface such as a frosted window or the surface of a frosted or coated light bulb.  
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