EGWR99: 10th Eurographics Workshop on Rendering

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https://diglib.eg.org/handle/10.2312/379

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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.
Computing Visibility for Triangulated Panoramas
(The Eurographics Association, 1999) Fu, Chi-Wing; Wong, Tien-Tsin; Heng, Pheng-Ann; Dani Lischinski and Greg Ward Larson
A visibility algorithm for triangulated panoramas is proposed. The algorithm can correctly resolve the visibility without making use of any depth information. It is especially useful when depth information is not available, such as in the case of real-world photographs. Based on the optical flow information and the image intensity, the panorama is subdivided into variable-sized triangles, image warping is then efficiently applied on these triangles using existing graphics hardware. The visibility problem is resolved by drawing the warped triangles in a specific order. This drawing order is derived from epipolar geometry. Using this partial drawing order, a graph can be built and topological sorting is applied on the graph to obtain the complete drawing order of all triangles. We will show that the time complexity of graph construction and topological sorting are both linear to the total number of triangles.
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.
Disruptive Technologies in Computer Graphics: Past, Present, and Future
(The Eurographics Association, 1999) Greenberg, Donald P.; Dani Lischinski and Greg Ward Larson
The history and famous landmarks of computer graphics hardware are well known. Starting with Ivan Sutherland s Sketchpad system in the early 1960 s, the first generation of computer graphics hardware consisted of calligraphic (vector) displays capable of drawing complex three-dimensional wireframe models at interactive rates. In the early 1970 s expensive color frame buffers with the capability for displaying static color images were introduced. Although more and more intelligence was added to these frame buffers, Jim Clark s geometry engine and the first graphics workstations were not introduced until the 1980 s. During the 1970 s, only the very costly and specialized hardware used for military and aerospace simulations was capable of real-time surface color display.
Effective Compression Techniques for Precomputed Visibility
(The Eurographics Association, 1999) Panne, Michiel van de; Stewart, A. James; Dani Lischinski and Greg Ward Larson
In rendering large models, it is important to identify the small subset of primitives that is visible from a given viewpoint. One approach is to partition the viewpoint space into viewpoint cells, and then precompute a visibility table which explicitly records for each viewpoint cell whether or not each primitive is potentially visible. We propose two algorithms for compressing such visibility tables in order to produce compact and natural descriptions of potentially-visible sets. Alternatively, the algorithms can be thought of as techniques for clustering cells and clustering primitives according to visibility criteria. The algorithms are tested on three types of scenes which have very different structures: a terrain model, a building model, and a world consisting of curved tunnels. The results show that the natural structure of each type of scene can automatically be exploited to achieve a compact representation of potentially visible sets.
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.
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.
Gathering for Free in RandomWalk Radiosity
(The Eurographics Association, 1999) Sbert, Mateu; Brusi, Alex; Bekaert, Philippe; Dani Lischinski and Greg Ward Larson
We present a simple technique that improves the efficiency of random walk algorithms for radiosity. Each generated random walk is used to simultaneously sample two distinct radiosity estimators. The first estimator is the commonly used shooting estimator, in which the radiosity due to self-emitted light at the origin of the random walk is recorded at each subsequently visited patch. With the second estimator, the radiosity due to self-emitted light at subsequent destinations is recorded at each visited patch. Closed formulae for the variance of the involved estimators allow to derive a cheap heuristic for combining the resulting radiosity estimates. Empirical results agree well with the heuristic prediction. A fair error reduction is obtained at a negligible additional cost.
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.
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.
Hierarchical Image-Based Rendering using Texture Mapping Hardware
(The Eurographics Association, 1999) Max, Nelson; Deussen, Oliver; Keating, Brett; Dani Lischinski and Greg Ward Larson
Multi-layered depth images containing color and normal information for subobjects in a hierarchical scene model are precomputed with standard zbuffer hardware for six orthogonal views. These are adaptively selected according to the proximity of the viewpoint, and combined using hardware texture mapping to create reprojected output images for new viewpoints. (If a subobject is too close to the viewpoint, the polygons in the original model are rendered.) Specific z-ranges are selected from the textures with the hardware alpha test to give accurate 3D reprojection. The OpenGL color matrix is used to transform the precomputed normals into their orientations in the final view, for hardware shading.
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.
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.
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.
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.
Interactive Rendering using the Render Cache
(The Eurographics Association, 1999) Walter, Bruce; Drettakis, George; Parker, Steven; Dani Lischinski and Greg Ward Larson
Interactive rendering requires rapid visual feedback. The render cache is a new method for achieving this when using high-quality pixel-oriented renderers such as ray tracing that are usually considered too slow for interactive use. The render cache provides visual feedback at a rate faster than the renderer can generate complete frames, at the cost of producing approximate images during camera and object motion. The method works both by caching previous results and reprojecting them to estimate the current image and by directing the renderer s sampling to more rapidly improve subsequent images. Our implementation demonstrates an interactive application working with both ray tracing and path tracing renderers in situations where they would normally be considered too expensive. Moreover we accomplish this using a software only implementation without the use of 3D graphics hardware.
Interactive Rendering with Arbitrary BRDFs using Separable Approximations
(The Eurographics Association, 1999) Kautz, Jan; McCool, Michael D.; Dani Lischinski and Greg Ward Larson
A separable decomposition of bidirectional reflectance distributions (BRDFs) is used to implement arbitrary reflectances from point sources on existing graphics hardware. Two-dimensional texture mapping and compositing operations are used to reconstruct samples of the BRDF at every pixel at interactive rates. A change of variables, the Gram-Schmidt halfangle/difference vector parameterization, improves separability. Two decomposition algorithms are also presented. The singular value decomposition (SVD) minimizes RMS error. The normalized decomposition is fast and simple, using no more space than what is required for the final representation.
Interactive Virtual Relighting and Remodeling of Real Scenes
(The Eurographics Association, 1999) Loscos, Céline; Frasson, Marie-Claude; Drettakis, George; Walter, Bruce; Granier, Xavier; Poulin, Pierre; Dani Lischinski and Greg Ward Larson
Lighting design is often tedious due to the required physical manipulation of real light sources and objects. As an alternative, we present an interactive system to virtually modify the lighting and geometry of scenes with both real and synthetic objects, including mixed real/virtual lighting and shadows. In our method, real scene geometry is first approximately reconstructed from photographs. Additional images are taken from a single viewpoint with a real light in different positions to estimate reflectance. A filtering process is used to compensate for inaccuracies, and per image reflectances are averaged to generate an approximate reflectance image for the given viewpoint, removing shadows in the process. This estimate is used to initialise a global illumination hierarchical radiosity system, representing real-world secondary illumination; the system is optimized for interactive updates. Direct illumination from lights is calculated separately using ray-casting and a table for efficient reuse of data where appropriate. Our system allows interactive modification of light emission and object positions, all with mixed real/virtual illumination effects. Real objects can also be virtually removed using texture-filling algorithms for reflectance estimation.
Light Field Techniques for Reflections and Refractions
(The Eurographics Association, 1999) Heidrich, Wolfgang; Lensch, Hendrik; Cohen, Michael F.; Seidel, Hans-Peter; Dani Lischinski and Greg Ward Larson
Reflections and refractions are important visual effects that have long been considered too costly for interactive applications. Although most contemporary graphics hardware supports reflections off curved surfaces in the form of environment maps, refractions in thick, solid objects cannot be handled with this approach, and the simplifying assumptions of environment maps also produce visible artifacts for reflections. Only recently have researchers developed techniques for the interactive rendering of true reflections and refractions in curved objects. This paper introduces a new, light field based approach to achieving this goal. The method is based on a strict decoupling of geometry and illumination. Hardware support for all stages of the technique is possible through existing extensions of the OpenGL rendering pipeline. In addition, we also discuss storage issues and introduce methods for handling vector-quantized data with graphics hardware.

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