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Item Rendering Translucent Materials Using Photon Diffusion(The Eurographics Association, 2007) Donner, Craig; Jensen, Henrik Wann; Jan Kautz and Sumanta PattanaikWe present a new algorithm for rendering translucent materials that combines photon tracing with diffusion. This combination makes it possible to efficiently render highly scattering translucent materials while accounting for internal blockers, complex geometry, translucent inter-scattering, and transmission and refraction of light at the boundary causing internal caustics. These effects cannot be accounted for with previous rendering approaches using the dipole or multipole diffusion approximations that only sample the incident illumination at the surface of the material. Instead of sampling lighting at the surface we trace photons into the material and store them volumetrically at their first scattering interaction with the material. We hierarchically integrate the diffusion of light from the photons to compute the radiant emittance at points on the surface of the material. For increased accuracy we use the incidence plane of the photon and the viewpoint on the surface to blend between three analytic diffusion approximations that best describe the geometric configuration between the photon and the shading point. For this purpose we introduce a new quadpole diffusion approximation that models diffusion at right angled edges, and an attenuation kernel to more accurately model multiple scattering near a light source. The photon diffusion approach is as efficient as previous Monte Carlo sampling approaches based on the dipole or multipole diffusion approximations, and our results demonstrate that it is more accurate and capable of capturing several illumination effects previously ignored when simulating the diffusion of light in translucent materials.Item Reverse Engineering Nature(The Eurographics Association and Blackwell Publishing Ltd, 2007) Jensen, Henrik WannWhy is the sky blue? Why is grass green? What determines the color of human skin? Questions such as these are increasingly important in the development of the next generation algorithms for appearancemodeling in computer graphics. By closely simulating the natural world around us we can develop algorithms that are useful in areas not traditionally connected with computer graphics. An example could be the ability to predict the color of human skin in the presence of certain diseases.In this talk, I will describe some of our recentwork in simulating the appearance of materials such as human skin, milk, and ice. This includes new research for predicting the appearance of materials based on their molecular structure in order to answer the question: what will it look like if I mix these molecules together ?