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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 Rendering of Wet Materials(The Eurographics Association, 1999) Jensen, Henrik Wann; Legakis, Justin; Dorsey, Julie; Dani Lischinski and Greg Ward LarsonThe appearance of many natural materials is largely influenced by the environment in which they are situated. Capturing the effects of such environmental factors is essential for producing realistic synthetic images. In this work, we model the changes of appearance due to one such environmental factor, the presence of water or other liquids. Wet materials can look darker, brighter, or more specular depending on the type of material and the viewing conditions. These differences in appearance are caused by a combination of the presence of liquid on the surface and inside the material. To simulate both of these conditions we have developed an approach that combines a reflection model for surface water with subsurface scattering. We demonstrate our approach with a variety of example scenes, showcasing many characteristic appearances of wet materials.Item Time Dependent Photon Mapping(The Eurographics Association, 2002) Cammarano, Mike; Jensen, Henrik Wann; P. Debevec and S. GibsonThe photon map technique for global illumination does not specifically address animated scenes. In particular, prior work has not considered the problem of temporal sampling (motion blur) while using the photon map. In this paper we examine several approaches for simulating motion blur with the photon map. In particular we show that a distribution of photons in time combined with the standard photon map radiance estimate is incorrect, and we introduce a simple generalization that correctly handles photons distributed in both time and space. Our results demonstrate that this time dependent photon map extension allows fast and correct estimates of motion-blurred illumination including motion-blurred caustics.Item A Spectral BSSRDF for Shading Human Skin(The Eurographics Association, 2006) Donner, Craig; Jensen, Henrik Wann; Tomas Akenine-Moeller and Wolfgang HeidrichWe present a novel spectral shading model for human skin. Our model accounts for both subsurface and surface scattering, and uses only four parameters to simulate the interaction of light with human skin. The four parameters control the amount of oil, melanin and hemoglobin in the skin, which makes it possible to match specific skin types. Using these parameters we generate custom wavelength dependent diffusion profiles for a two-layer skin model that account for subsurface scattering within the skin. These diffusion profiles are computed using convolved diffusion multipoles, enabling an accurate and rapid simulation of the subsurface scattering of light within skin. We combine the subsurface scattering simulation with a Torrance-Sparrow BRDF model to simulate the interaction of light with an oily layer at the surface of the skin. Our results demonstrate that this four parameter model makes it possible to simulate the range of natural appearance of human skin including African, Asian, and Caucasian skin types.Item Photon Mapping on Programmable Graphics Hardware(The Eurographics Association, 2003) Purcell, Timothy J.; Donner, Craig; Cammarano, Mike; Jensen, Henrik Wann; Hanrahan, Pat; M. Doggett and W. Heidrich and W. Mark and A. SchillingWe present a modified photon mapping algorithm capable of running entirely on GPUs. Our implementation uses breadth-first photon tracing to distribute photons using the GPU. The photons are stored in a grid-based photon map that is constructed directly on the graphics hardware using one of two methods: the first method is a multipass technique that uses fragment programs to directly sort the photons into a compact grid. The second method uses a single rendering pass combining a vertex program and the stencil buffer to route photons to their respective grid cells, producing an approximate photon map. We also present an efficient method for locating the nearest photons in the grid, which makes it possible to compute an estimate of the radiance at any surface location in the scene. Finally, we describe a breadth-first stochastic ray tracer that uses the photon map to simulate full global illumination directly on the graphics hardware. Our implementation demonstrates that current graphics hardware is capable of fully simulating global illumination with progressive, interactive feedback to the user.Item Rendering Caustics on Non-Lambertian Surfaces(Blackwell Publishers Ltd and the Eurographics Association, 1997) Jensen, Henrik WannThis paper presents a new technique for rendering caustics on non-Lambertian surfaces. The method is based on an extension of the photon map which removes previous restrictions limiting the usage to Lambertian surfaces. We add information about the incoming direction to the photons and this allows us to combine the photon map with arbitrary reflectance functions. By using a cone-filter we improve the quality of the radiance estimate in particular at discontinuities. Furthermore we introduce balancing of the photon map which not only reduces the memory requirements but also significantly reduces the rendering time. We have used the method to render caustics on surfaces with reflectance functions varying from Lambertian to glossy specular.