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Ray Tracing Volume Densities
, 1984
"... This paper presents new algorithms to trace objects represented by densities within a volume grid, e.g. clouds, fog, flames, dust, particle systems. We develop the light scattering equations, discuss previous methods of solution, and present a new approximate solution to the full threedimensional ..."
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Cited by 257 (0 self)
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This paper presents new algorithms to trace objects represented by densities within a volume grid, e.g. clouds, fog, flames, dust, particle systems. We develop the light scattering equations, discuss previous methods of solution, and present a new approximate solution to the full threedimensional radiative scattering problem suitable for use in computer graphics. Additionally we review dynamical models for clouds used to make an animated movie.
A Model for Anisotropic Reflection
"... A reflection and refraction model for anisotropic surfaces is introduced. The anisotropy is simulated by small cylinders (added or subtracted) distributed on the anisotropic surface. Different levels of anisotropy are achieved by varying the distance between each cylinder and/or rising the cylinders ..."
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Cited by 104 (4 self)
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A reflection and refraction model for anisotropic surfaces is introduced. The anisotropy is simulated by small cylinders (added or subtracted) distributed on the anisotropic surface. Different levels of anisotropy are achieved by varying the distance between each cylinder and/or rising the cylinders more or less from the surface. Multidirectional anisotropy is modelled by orienting groups of cylinders in different direction. The intensity of the reflected light is computed by determining the visible and illuminated portion of the cylinders, taking selfblocking into account. We present two techniques to compute this in practice. In one the intensity is computed by sampling the surface of the cylinders. The other is an analytic solution. In the case of the diffuse component, the solution is exact. In the case of the specular component, an approximation is developed using a Chebyshev polynomial approximation of the specular term, and integrating the polynomial. This model can be implemented easily within most rendering system, given a suitable mechanism to define and alter surface tangents. The effectiveness of the model and the visual importance of anisotropy are illustrated with some pictures.
Appendix  Projective Geometry for Machine Vision
, 1992
"... Introduction The idea for this Appendix arose from our perception of a frustrating situation faced by vision researchers. For example, one is interested in some aspect of the theory of perspective image formation such as the epipolar line. The interested party goes to the library to check out a boo ..."
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Cited by 36 (0 self)
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Introduction The idea for this Appendix arose from our perception of a frustrating situation faced by vision researchers. For example, one is interested in some aspect of the theory of perspective image formation such as the epipolar line. The interested party goes to the library to check out a book on projective geometry filled with hope that the necessary mathematical machinery will be directly at hand. These expectations are quickly dashed. Upon opening the book, the expectant reader finds the presentation dominated by endless observations about harmonic relations and a few chapters which explore the minutiae of Pappus' theorem. Finally, as a last cruel twist of irony, the book ends in triumph with a rather exhilarating discourse on the conic pencil. All of the material is presented in the form of theorems defined on points, lines and conics without the use of coordinates, except perhaps for a quick pause to define barycentric coordinates just to taunt the reader. Dejected, the vis
Adaptive Grid for Polyhedral Visibility in Object Space: An Implementation
, 1986
"... This paper presents an implementation of Franklin's object space hidden surface algorithm for polyhedral scenes [ACM Computer Graphics 14(3), 117123, 1980]. It is known that if the faces are independently and identically distributed this algorithm performs in time linear in the number of faces ..."
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Cited by 5 (2 self)
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This paper presents an implementation of Franklin's object space hidden surface algorithm for polyhedral scenes [ACM Computer Graphics 14(3), 117123, 1980]. It is known that if the faces are independently and identically distributed this algorithm performs in time linear in the number of faces and in particular, is not affected by the depth complexity. The algorithm overlays a grid on the scene with fineness depending on the statistics of the edges and the faces. It then preprocesses the edges and the faces in a grid data structure so that distant edges and faces will not be compared.
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"... We present a solution to the aliasing problem for shadow algorithms that use depth maps. The solution is based on a new filtering technique called percentage closer filtering. In addition to antialiasing, the improved algorithm provides soft shadow boundaries that resemble penumbrae. We describe t ..."
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We present a solution to the aliasing problem for shadow algorithms that use depth maps. The solution is based on a new filtering technique called percentage closer filtering. In addition to antialiasing, the improved algorithm provides soft shadow boundaries that resemble penumbrae. We describe the new algorithm in detail, demonstrate the effects of its parameters, and analyze its performance.
Adaptive Radiosity Textures for Bidirectional Ray Tracing
"... We present a rendering method designed to provide accurate, general simulation of global illumination for realistic image synthesis. Separating surface interaction into diffuse plus specular, we compute the specular component on the fly, as in ray tracing, and store the diffuse component (the radi ..."
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We present a rendering method designed to provide accurate, general simulation of global illumination for realistic image synthesis. Separating surface interaction into diffuse plus specular, we compute the specular component on the fly, as in ray tracing, and store the diffuse component (the radiosity) for laterreuse, similar to a radiosity algorithm. Radiosities are stored in adaptive radiosity tezlures (fezes) that record the pattern of light and shadow on every diffuse surface in the scene. They adaptively subdivide themselves to the appropriate level of detail for the picture being made, resolving sharp shadow edges automatically. We use a threepass, bidirectional ray tracing algorithm that traces rays from both the lights and the eye. The &quot;size pass &quot; records visibility iufornmtion on diffuse surfaces; the &quot;light pass &quot; progressively traces rays from lights and bright surfaces to deposit photons on diffuse surfaces to construct the radiosity textures; and the &quot;eye pass &quot; traces rays from the eye, collecting light from diffuse surfaces to make a picture.
A Distributed Graphics Library System
"... We present a set of library routines that allow easily parallelized graphics rendering routines that require no communication between each parallel task, such as raytracing, to be run eciently in an environment of distributed workstations. The presentation of the paper focuses on the problems encou ..."
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We present a set of library routines that allow easily parallelized graphics rendering routines that require no communication between each parallel task, such as raytracing, to be run eciently in an environment of distributed workstations. The presentation of the paper focuses on the problems encountered in implementing a distributed system under Unix and proposes solutions to each problem. Specifically, we discuss the challenges involved in overcoming the limits of communicating with a large number of processes in Unix and in providing fault tolerance when using sockets. Technical aspects of the implementation and some additional problems that were encountered are discussed. Finally, we compare the rendering times for a complex image with a renderer using the library and show that the library routines are able to exploit much of the existing parallelism. The library is presented using a graphics application, though the concepts are generic enough to be of use in designing any distributed system under Unix.