EGWR: Eurographics Workshop on Rendering

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Approximating the Location of Integrand Discontinuities for Penumbral Illumination with Area Light Sources
(The Eurographics Association, 1999) Ouellette, Marc J.; Fiume, Eugene; Dani Lischinski and Greg Ward Larson
The problem of computing soft shadows with area light sources has received considerable attention in computer graphics. In part, this is a difficult problem because the integral that defines the radiance at a point must take into account the visibility function. Most of the solutions proposed have been limited to polygonal environments, and require a full visibility determination preprocessing step. The result is typically a partitioning of the environment into regions that have a similar view of the light source. We propose a new approach that can be successfully applied to arbitrary environments. The approach is based on the observation that, in the presence of occluders, the primary difficulty in computing the integral that defines the contribution of an area light source, is that of determining the visible domain of the integrand. We extend a recent shadow algorithm for linear light sources in order to calculate a polygonal approximation to this visible domain. We demonstrate for an important class of shadowing problems, and in particular, for convex occluders, that the shape of the visible domain only needs to be roughly approximated by a polygonal boundary. We then use this boundary to subdivide an area light source into a small number of triangles that can be integrated efficiently using either a deterministic solution, or a low degree numerical cubature.
Beyond Photorealism
(The Eurographics Association, 1999) Green, Stuart; Dani Lischinski and Greg Ward Larson
For around 30 years the computer graphics research community has pursued photorealism as though it were the ultimate form of visual expression. Yet, as an art form, photorealism is one of many abstrations that an artist might use to convey ideas, shape, structure, emotion and mood. In this paper we describe how techniques and wisdom learned from photorealistic computer graphics can be adapted and applied to a diverse range of alternative styles for visual expression.
Image-Based BRDF Measurement Including Human Skin
(The Eurographics Association, 1999) Marschner, Stephen R.; Westin, Stephen H.; Lafortune, Eric P. F.; Torrance, Kenneth E.; Greenberg, Donald P.; Dani Lischinski and Greg Ward Larson
We present a new image-based process for measuring the bidirectional reflectance of homogeneous surfaces rapidly, completely, and accurately. For simple sample shapes (spheres and cylinders) the method requires only a digital camera and a stable light source. Adding a 3D scanner allows a wide class of curved near-convex objects to be measured. With measurements for a variety of materials from paints to human skin, we demonstrate the new method s ability to achieve high resolution and accuracy over a large domain of illumination and reflection directions. We verify our measurements by tests of internal consistency and by comparison against measurements made using a gonioreflectometer.
Real-Time Rendering of Real World Environments
(The Eurographics Association, 1999) McAllister, David K.; Nyland, Lars; Popescu, Voicu; Lastra, Anselmo; McCue, Chris; Dani Lischinski and Greg Ward Larson
One of the most important goals of interactive computer graphics is to allow a user to freely walk around a virtual recreation of a real environment that looks as real as the world around us. But hand-modeling such a virtual environment is inherently limited and acquiring the scene model using devices also presents challenges. Interactively rendering such a detailed model is beyond the limits of current graphics hardware, but image-based approaches can significantly improve the status quo. We present an end-to-end system for acquiring highly detailed scans of large real world spaces, consisting of forty to eighty million range and color samples, using a digital camera and laser rangefinder. We explain successful techniques to represent these large data sets as image-based models and present contributions to image-based rendering that allow these models to be rendered in real time on existing graphics hardware without sacrificing the high resolution at which the data sets were acquired.
Rendering Inhomogeneous Surfaces with Radiosity
(The Eurographics Association, 1999) Mostefaoui, L.; Dischler, J.M.; Ghazanfarpour, D.; Dani Lischinski and Greg Ward Larson
Natural surfaces are often complex: they nearly always exhibit small scale imperfections such as dirt, dust, cracks, etc., as well as large scale structural elements, as for wickerwork, brick walls, textiles, pebbles, etc., that are generally too complex to be modeled explicitly. In this paper, we propose a new multi-scale periodic texture model adapted to the efficient simulation of the previously mentioned features. This new model combines notions of virtual ray tracing (that we have recently introduced) with bi-directional texture function, while it also considers self-shadowing and inter-reflections at texture scale. In a second step, the texture model is integrated into hierarchical radiosity with clustering. Therefore, an extension of radiosity techniques, currently limited to texture maps, bump maps and general (homogeneous) reflectance functions, is proposed. The final rendering consists of applying a second ray tracing pass, based on a gathering methodology adapted to the model. The method provides images at a significant lower computation and memory consumption cost than with explicit models in the case of periodic features (wickerwork, grids, pavements, etc.) for a similar visual quality.
Rendering of Wet Materials
(The Eurographics Association, 1999) Jensen, Henrik Wann; Legakis, Justin; Dorsey, Julie; Dani Lischinski and Greg Ward Larson
The 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.
Efficient Displacement Mapping by Image Warping
(The Eurographics Association, 1999) Schaufler, Gernot; Priglinger, Markus; Dani Lischinski and Greg Ward Larson
While displacement maps can provide a rich set of visual detail on otherwise simple surfaces, they have always been very expensive to render. Rendering has been done using ray-tracing and by introducing a great number of micro-polygons. We present a new image-based approach by showing that rendering displacement maps is sufficiently similar to image warping for parallel displacements and displacements originating form a single point. Our new warping algorithm is particularly well suited for this class of displacement maps. It allows efficient modeling of complicated shapes with few displacement mapped polygons and renders them at interactive rates.
Shadow Penumbras for Complex Objects by Depth-Dependent Filtering of Multi-Layer Depth Images
(The Eurographics Association, 1999) Keating, Brett; Max, Nelson; Dani Lischinski and Greg Ward Larson
This paper presents an efficient algorithm for filtering multi-layer depth images (MDIs) in order to produce approximate penumbras. The filtering is performed on a MDI that represents the view from the light source. The algorithm is based upon both ray tracing and the z-buffer shadow algorithm, and is closely related to convolution methods. The method s effectiveness is demonstrated on especially complex objects such as trees, whose soft shadows are expensive to compute by other methods. The method specifically addresses the problem of light-leaking that occurs when tracing rays through discrete representations, and the inability of convolution methods to produce accurate self-shadowing effects.
Group Accelerated Shooting Methods for Radiosity
(The Eurographics Association, 1999) Rousselle, Francois; Renaud, Christophe; Dani Lischinski and Greg Ward Larson
The introduction of the Progressive Refinement method was the starting point of interactivity in the radiosity illumination process. Overshooting methods brought an important acceleration to the convergence particularly for scenes with a high mean reflectivity. In this paper we present a new acceleration technique to PR and overshooting methods based on group shooting methods. The acceleration is obtained by occasionally selecting groups of interacting patches and by solving the subsystem built from this group. This technique allows us to reduce the number of iterations that are required to solve the radiosity system and only involves a small computation overhead. Comparing different algorithms for scenes with particular properties, we highlight interesting results of the Group Accelerated Shooting Methods especially when considering complex scenes with many occlusions.
Interactive Ray-Traced Scene Editing Using Ray Segment Trees
(The Eurographics Association, 1999) Bala, Kavita; Dorsey, Julie; Teller, Seth; Dani Lischinski and Greg Ward Larson
This paper presents a ray tracer that facilitates near-interactive scene editing with incremental rendering; the user can edit the scene both by manipulating objects and by changing the viewpoint. Our system uses object-space radiance interpolants to accelerate ray tracing by approximating radiance, while bounding error. We introduce a new hierarchical data structure, the ray segment tree (RST), which tracks the dependencies of radiance interpolants on regions of world space. When the scene is edited, affected interpolants are rapidly identified typically in 0.1 seconds by traversing these ray segment trees. The affected interpolants are updated and used to re-render the scene with a 3 to 4 speedup over the base ray tracer, even when the viewpoint is changed. Although the system does no pre-processing, performance is better than for the base ray tracer even on the first rendered frame.
An Illumination Model for a System of Isotropic Substrate- Isotropic Thin Film with Identical Rough Boundaries
(The Eurographics Association, 1999) Icart, Isabelle; Arqués, Didier; Dani Lischinski and Greg Ward Larson
A new physically-based illumination model describing the interaction of light with a system composed of an isotropic substrate coated by an isotropic film with geometrically identical statistical rough boundaries (ITF) is presented. This model divides the intensity reflected from the system into three components: specular, directional-diffuse and uniform diffuse intensity. The formulas for the intensity reflected coherently (specular) and incoherently (directionaldiffuse) from the system are derived within the framework of the scalar diffraction theory. Assuming that the slopes on the boundaries of the film are small, a first-order expansion of the reflection coefficient is used in the evaluation of the Helmholtz-Kirchhoff integral which allows to calculate the previous intensities. The consistency of the model is evaluated numerically and appraised visually by comparison with classic approximations.
Perceptually-informed accelerated rendering of high quality walkthrough sequences
(The Eurographics Association, 1999) Myszkowski, Karol; Rokita, Przemyslaw; Tawara, Takehiro; Dani Lischinski and Greg Ward Larson
In this paper, we consider accelerated rendering of walkthrough animation sequences using combination of ray tracing and Image-Based Rendering (IBR) techniques. Our goal is to derive as many pixels as possible using inexpensive IBR techniques without affecting the animation quality. A perception-based spatio-temporal Animation Quality Metric (AQM) is used to automatically guide such a hybrid rendering. The Pixel Flow (PF) obtained as a by-product of the IBR computation is an integral part of the AQM. The final animation quality is enhanced by an efficient spatio-temporal antialiasing, which utilize the PF to perform a motion-compensated filtering.
Multiple Textures Stitching and Blending on 3D Objects
(The Eurographics Association, 1999) Rocchini, C.; Cignoni, P.; Montani, C.; Scopigno, R.; Dani Lischinski and Greg Ward Larson
In this paper we propose a new approach for mapping and blending textures on 3D geometries. The system starts from a 3D mesh which represents a real object and improves this model with pictorial detail. Texture detail is acquired via a common photographic process directly from the real object. These images are then registered and stitched on the 3D mesh, by integrating them into a single standard texture map. An optimal correspondence between regions of the 3D mesh and sections of the acquired images is built. Then, a new approach is proposed to produce a smooth join between different images that map on adjacent sections of the surface, based on texture blending. For each mesh face which is on the adjacency border between different observed images, a corresponding triangular texture patch is resampled as a weighted blend of the corresponding adjacent images sections. The accuracy of the resampling and blending process is improved by computing an accurate piecewise local registration of the original images with respect to the current face vertices. Examples of the results obtained with sample Cultural Heritage objects are presented and discussed.
Lighting Design: A Goal Based Approach Using Optimisation
(The Eurographics Association, 1999) Costa, António Cardoso; Sousa, António Augusto; Ferreira, Fernando Nunes; Dani Lischinski and Greg Ward Larson
There is a need for reliable lighting design applications because available tools are limited and inappropriate for interactive or creative use. Architects and lighting designers need those applications to define, predict, test and validate lighting solutions for their problems. We present a new approach to the lighting design problem based on a methodology that includes the geometry of the scene, the properties of materials and the design goals. It is possible to obtain luminaire characteristics or other kind of results that maximise the attainment of the design goals, which may include different types of constraints or objectives (lighting, geometrical or others). The main goal, in our approach, is to improve the lighting design cycle. In this work we discuss the use of optimisation in lighting design, describe the implementation of the methodology, present real-world based examples and analyse in detail some of the complex technical problems associated and speculate on how to overcome them.
Decoupling Polygon Rendering from Geometry using Rasterization Hardware
(The Eurographics Association, 1999) Westermann, Rüdiger; Sommer, Ove; Ertl, Thomas; Dani Lischinski and Greg Ward Larson
The dramatically increasing size of polygonal models resulting from 3D scanning devices and advanced modeling techniques requires new approaches to reduce the load of geometry transfer and processing. In order to supplement methods like polygon reduction or geometry compression we suggest to exploit the processing power and functionality of the rasterization and texture subsystem of advanced graphics hardware. We demonstrate that 3D-texture maps can be used to render voxelized polygon models of arbitrary complexity at interactive rates by extracting isosurfaces from distance volumes. Therefore, we propose two fundamental algorithms to limit the rasterization load: First, the model is partitioned into a hierarchy of axis-aligned bounding boxes that are voxelized in an error controlled multi-resolution representation. Second, rasterization is restricted to the thin boundary regions around the isosurface representing the voxelized geometry. Furthermore, we suggest and simulate an OpenGL extension enabling advanced per-pixel lighting and shading. Although the presented approach exhibits certain limitations we consider it as a starting point for hybrid solutions balancing load between the geometry and the rasterization stage and we expect some influence on future hardware design.
Face Cluster Radiosity
(The Eurographics Association, 1999) Willmott, Andrew J.; Heckbert, Paul S.; Garland, Michael; Dani Lischinski and Greg Ward Larson
An algorithm for simulating diffuse interreflection in complex three dimensional scenes is described. It combines techniques from hierarchical radiosity and multiresolution modelling. A new face clustering technique for automatically partitioning polygonal models is used. The face clusters produced group adjacent triangles with similar normal vectors. They are used during radiosity solution to represent the light reflected by a complex object at multiple levels of detail. Also, the radiosity method is reformulated in terms of vector irradiance and power. Together, face clustering and the vector formulation of radiosity permit large savings. Excessively fine levels of detail are not accessed by the algorithm during the bulk of the solution phase, greatly reducing its memory requirements relative to previous methods. Consequently, the costliest steps in the simulation can be made sub-linear in scene complexity. Using this algorithm, radiosity simulations on scenes of one million input polygons can be computed on a standard workstation.
Space-Time Hierarchical Radiosity
(The Eurographics Association, 1999) Damez, Cyrille; Sillion, Francois; Dani Lischinski and Greg Ward Larson
This paper presents a new hierarchical simulation algorithm allowing the calculation of radiosity solutions for time-dependent scenes where all motion is known a priori. Such solutions could, for instance, be computed to simulate subtle lighting effects (indirect lighting) in animation systems, or to obtain highquality synthetic image sequences to blend with live action video and film. We base our approach on a Space-Time hierarchy, adding a life span to hierarchical surface elements, and present an integrated formulation of Hierarchical Radiosity with this extended hierarchy. We discuss the expected benefits of the technique, review the challenges posed by the approach, and propose first solutions for these issues, most notably for the space-time refinement strategy. We show that a short animation sequence can be computed rapidly at the price of a sizeable memory cost. These results confirm the potential of the approach while helping to identify areas of promising future work.
Information Theory Tools for Scene Discretization
(The Eurographics Association, 1999) Feixas, Miquel; Acebo, Esteve del; Bekaert, Philippe; Sbert, Mateu; Dani Lischinski and Greg Ward Larson
Finding an optimal discretization of a scene is an important but difficult problem in radiosity. The efficiency of hierarchical radiosity for instance, depends entirely on the subdivision criterion and strategy that is used. We study the problem of adaptive scene discretization from the point of view of information theory. In previous work, we have introduced the concept of mutual information, which represents the information transfer or correlation in a scene, as a complexity measure and presented some intuitive arguments and preliminary results concerning the relation between mutual information and scene discretization. In this paper, we present a more general treatment supporting and extending our previous findings to the level that the development of practical information theory-based tools for optimal scene discretization becomes feasible.
Towards Interactive Photorealistic Rendering of Indoor Scenes: A Hybrid Approach
(The Eurographics Association, 1999) Udeshi, Tushar; Hansen, Charles D.; Dani Lischinski and Greg Ward Larson
Photorealistic rendering methods produce accurate solutions to the rendering equation but are computationally expensive and typically noninteractive. Some researchers have used graphics hardware to obtain photorealistic effects but not at interactive frame rates. We describe a technique to achieve near photorealism of simple indoor scenes at interactive rates using both CPUs and graphics hardware in parallel. This allows the user the ability to interactively move objects and lights in the scene. Our goal is to introduce as many global illumination effects as possible while maintaining a high frame rate. We describe methods to generate soft shadows, approximate one-bounce indirect lighting, and specular reflection and refraction effects.
Geospecific rendering of alpine terrain
(The Eurographics Association, 1999) Premoze, Simon; Thompson, William B.; Shirley, Peter; Dani Lischinski and Greg Ward Larson
Realistic rendering of outdoor terrain requires both that the geometry of the environment be modeled accurately and that appropriate texturing be laid down on top of that geometry. While elevation data is widely available for much of the world and many methods exist for converting this data to forms suitable for graphics systems, we have much less experience with patterning the resulting surface. This paper describes an approach for using panchromatic (grayscale) aerial imagery to produce color views of alpine scenes. The method is able to remove shading and shadowing effects in the original image so that shading and shadowing appropriate to variable times of day can be added. Seasonal snow cover can be added in a physically plausible manner. Finally, 3 D instancing of trees and brush can be added in locations consistent with the imagery, significantly improving the visual quality.

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