François X. Sillion
Cornell University
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Featured researches published by François X. Sillion.
international conference on computer graphics and interactive techniques | 1991
Xiao Dong He; Kenneth E. Torrance; François X. Sillion; Donald P. Greenberg
A new general reflectance model for computer graphics is presented. The model is based on physical optics and describes specular, directional diffuse, and uniform diffuse reflection by a surface. The reflected light pattern depends on wavelength, incidence angle, two surface roughness parameters, and surface refractive index. The formulation is self consistent in terms of polarization, surface roughness, masking/shadowing, and energy. The model applies to a wide range of materials and surface finishes and provides a smooth transition from diffuse-like to specular reflection as the wavelength and incidence angle are increased or the surface roughness is decreased. The model is analytic and suitable for Computer Graphics applications. Predicted reflectance distributions compare favorably with experiment. The model is applied to metallic, nonmetallic, and plastic materials, with smooth and rough surfaces.
Computer Graphics Forum | 2003
Jean-Marc Hasenfratz; Marc Lapierre; Nicolas Holzschuch; François X. Sillion
ACM CSS: I.3.3 Computer Graphics Picture/Image Generation—Bitmap and framebuffer operations
international conference on computer graphics and interactive techniques | 1998
Cyril Soler; François X. Sillion
The calculation of detailed shadows remains one of the most difficult challenges in computer graphics, especially in the case of extended (linear or area) light sources. This paper introduces a new tool for the calculation of shadows cast by extended light sources. Exact shadows are computed in some constrained configurations by using a convolution technique, yielding a fast and accurate solution. Approximate shadows can be computed for general configurations by applying the convolution to a representative “ideal” configuration. We analyze the various sources of approximation in the process and derive a hierarchical, error driven algorithm for fast shadow calculation in arbitrary configurations using a hierarchy of object clusters. The convolution is performed on images rendered in an offscreen buffer and produces a shadow map used as a texture to modulate the unoccluded illumination. Light sources can have any 3D shape as well as arbitrary emission characteristics, while shadow maps can be applied to groups of objects at once. The method can be employed in a hierarchical radiosity system, or directly as a shadowing technique. We demonstrate results for various scenes, showing that soft shadows can be generated at interactive rates for dynamics environments.
international conference on computer graphics and interactive techniques | 1997
George Drettakis; François X. Sillion
In this paper we describe a unified data-structure, the 3D Visibility Complex which encodes the visibility information of a 3D scene of polygons and smooth convex objects. This datastructure is a partition of the maximal free segments and is based on the characterization of the topological changes of visibility along critical line sets. We show that the size k of the complex is (n) and O(n4) and we give an output sensitive algorithm to build it in time O((n3 + k) log n). This theoretical work has already been used to define a practical data-structure, the Visibility Skeleton described in a companion paper. Interactively manipulating the geometry of complex, globally illuminated scenes has to date proven an elusive goal. Previous attempts have failed to provide interactive updates of global illumination and have not been able to offer well-adapted algorithms controlling the frame rate. The need for such interactive updates of global illumination is becoming increasingly important as the field of application of radiosity algorithms widens. To address this need, we present a novel algorithm which provides interactive update rates of global illumination for complex scenes with moving objects. In the contact of clustering for hierarchical radiosity, we introduce the idea of an implicit line-space hierarchy. This hierarchy is realized by augmenting the links between hierarchical elements (clusters or surfaces) with shafts, representing the set of lines passing through the two linked elements. We show how line-space traversal allows rapid identification of modified links, and simultaneous cleanup of subdivision no longer required after a geometry move, by identifying the modified paths in the scene hierarchy. The implementation of our new algorithm allows interactive updates of illumination after object motion for scenes containing several thousand polygons, including global illumination effects. Finally, the line-space hierarchy traversal provides a natural control mechanism allowing the regulation of the tradeoff between image quality and frame rate.
IEEE Computer Graphics and Applications | 1990
David W. George; François X. Sillion; Donald P. Greenberg
The radiosity algorithm is extended to dynamic environments, providing global-illumination simulations to scenes that are modified interactively. The illumination effects introduced by a change in position, shape, or attributes of any object in the scene are computed very rapidly by redistributing the energy already exchanged between objects. Corrections are made by shooting positive and negative energy, accounting for increased illumination and the creation of shadows. Object coherence is used to minimize computation, and progressive-refinement techniques are used to accelerate convergence. The extended algorithm yields excellent approximations to the exact solutions at interactive speeds.<<ETX>>
eurographics | 1998
Cyril Soler; François X. Sillion
We propose a new method for greatly accelerating the computation of complex, detailed shadows in a radiosity solution. Radiosity is computed using a “standard” hierarchical radiosity algorithm with clustering, but the rapid illumination variations over some large regions receiving complex shadows are computed on the fly using an efficient convolution operation, and displayed as textures. This allows the representation of complex shadowed radiosity functions on a single large polygon. We address the main issues of efficiently and consistently integrating the soft shadow calculation in the hierarchical radiosity framework. These include the identification of the most appropriate mode of calculation for each particular configuration of energy exchange, the development of adequate refinement criteria for error-driven simulation, and appropriate data structures and algorithms for radiosity representation and display. We demonstrate the efficiency of the algorithm with examples involving complex scenes, and a comparison to a clustering algorithm.
applied perception in graphics and visualization | 2009
Pierre Bénard; Joëlle Thollot; François X. Sillion
Texture fractalization is used in many existing approaches to ensure the temporal coherence of a stylized animation. This paper presents the results of a psychological user-study evaluating the relative distortion induced by a fractalization process of typical medium textures. We perform a ranking experiment, assess the agreement among the participant and study the criteria they used. Finally we show that the average co-occurrence error is an efficient quality predictor in this context.
Graphics Gems II | 1991
François X. Sillion
Publisher Summary This chapter describes the detection of shadow boundaries for adaptive meshing in radiosity. Radiosity algorithms attempt to compute the global interreflection of light in an environment composed of diffuse surfaces. Most implementations of the radiosity approach break the surfaces in a scene into patches in a meshing stage, and these patches are used as secondary illuminators in the course of the solution. Radiosity textures also have been used to encode the illumination information without complicating the geometrical description. The radiosity across a patch typically is interpolated bilinearly from radiosities at the vertices, which means that the accuracy of the illumination on a surface is influenced directly by the size of the mesh elements. Typically, one would like to concentrate smaller elements in the regions of sharp intensity variations, such as shadow boundaries, while limiting the subdivision of surfaces with gentle illumination variations.
international conference on computer graphics and interactive techniques | 1996
François X. Sillion
Computer graphics is a very fast moving field throughout the world, and France is certainly no exception. While preparing this article, I discovered a half dozen graduate graphics courses that were offered for the first time this academic year. Considering the time that will elapse before this issue is sent to you, the reader, I will not claim to offer a complete view of computer graphics education in France. Rather, I would like to briefly explain the structure of the French education system, illustrate the recent evolution of the field and present a broad picture of the current offerings that revolve around computer graphics. More complete information on specific courses and programs, including some syllabi, can be found on-line as indicated below.Let me begin with the observation that French high schools are not typically very well equipped with computers. Therefore, we can consider that computer science (and computer graphics) education only begins at the higher education level. I shall start with a quick presentation of the French higher education and research system, this being necessary to understand the computer graphics education scene.
international conference on computer graphics and interactive techniques | 2003
Peter Wonka; Michael Wimmer; François X. Sillion; William Ribarsky