EGWR02: 13th Eurographics Workshop on Rendering

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https://diglib.eg.org/handle/10.2312/381

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Accelerating Path Tracing by Re-Using Paths
(The Eurographics Association, 2002) Bekaert, Philippe; Sbert, Mateu; Halton, John; P. Debevec and S. Gibson
This paper describes a new acceleration technique for rendering algorithms like path tracing, that use so called gathering random walks. Usually in path tracing, each traced path is used in order to compute a contribution to only a single point on the virtual screen. We propose to combine paths traced through nearby screen points in such a way that each path contributes to multiple screen points in a provably good way. Our approach is unbiased and is not restricted to diffuse light scattering. It complements previous image noise reduction techniques for Monte Carlo ray tracing. We observe speed-ups in the computation of indirect illumination of one order of magnitude.
Acquisition and Rendering of Transparent and Refractive Objects
(The Eurographics Association, 2002) Matusik, Wojciech; Pfister, Hanspeter; Ziegler, Remo; Ngan, Addy; McMillan, Leonard; P. Debevec and S. Gibson
This paper introduces a new image-based approach to capturing and modeling highly specular, transparent, or translucent objects. We have built a system for automatically acquiring high quality graphical models of objects that are extremely difficult to scan with traditional 3D scanners. The system consists of turntables, a set of cameras and lights, and monitors to project colored backdrops. We use multi-background matting techniques to acquire alpha and environment mattes of the object from multiple viewpoints. Using the alpha mattes we reconstruct an approximate 3D shape of the object. We use the environment mattes to compute a high-resolution surface reflectance field. We also acquire a low-resolution surface reflectance field using the overhead array of lights. Both surface reflectance fields are used to relight the objects and to place them into arbitrary environments. Our system is the first to acquire and render transparent and translucent 3D objects, such as a glass of beer, from arbitrary viewpoints under novel illumination.
Appearance based object modeling using texture database: Acquisition, compression and rendering
(The Eurographics Association, 2002) Furukawa, R.; Kawasaki, H.; Ikeuchi, K.; Sakauchi, M.; P. Debevec and S. Gibson
Image-based object modeling can be used to compose photorealistic images of modeled objects for various rendering conditions, such as viewpoint, light directions, etc. However, it is challenging to acquire the large number of object images required for all combinations of capturing parameters and to then handle the resulting huge data sets for the model. This paper presents a novel modeling method for acquiring and preserving appearances of objects. Using a specialized capturing platform, we first acquire objects geometrical information and their complete 4D indexed texture sets, or bi-directional texture functions (BTF) in a highly automated manner. Then we compress the acquired texture database using tensor product expansion. The compressed texture database facilitates rendering objects with arbitrary viewpoints, illumination, and deformation.
Approximate Soft Shadows on Arbitrary Surfaces using PenumbraWedges
(The Eurographics Association, 2002) Akenine-Möller, Tomas; Assarsson, Ulf; P. Debevec and S. Gibson
Shadow generation has been subject to serious investigation in computer graphics, and many clever algorithms have been suggested. However, previous algorithms cannot render high quality soft shadows onto arbitrary, animated objects in real time. Pursuing this goal, we present a new soft shadow algorithm that extends the standard shadow volume algorithm by replacing each shadow quadrilateral with a new primitive, called the penumbra wedge. For each silhouette edge as seen from the light source, a penumbra wedge is created that approximately models the penumbra volume that this edge gives rise to. Together the penumbra wedges can render images that often are remarkably close to more precisely rendered soft shadows. Furthermore, our new primitive is designed so that it can be rasterized efficiently. Many real-time algorithms can only use planes as shadow receivers, while ours can handle arbitrary shadow receivers. The proposed algorithm can be of great value to, e.g., 3D computer games, especially since it is highly likely that this algorithm can be implemented on programmable graphics hardware coming out within the next year, and because games often prefer perceptually convincing shadows.
Curve Analogies
(The Eurographics Association, 2002) Hertzmann, Aaron; Oliver, Nuria; Curless, Brian; Seitz, Steven M.; P. Debevec and S. Gibson
This paper describes a method for learning statistical models of 2D curves, and shows how these models can be used to design line art rendering styles by example. A user can create a new style by providing an example of the style, e.g. by sketching a curve in a drawing program. Our method can then synthesize random new curves in this style, and modify existing curves to have the same style as the example. This method can incorporate position constraints on the resulting curves.
Efficient High Quality Rendering of Point Sampled Geometry
(The Eurographics Association, 2002) Botsch, Mario; Wiratanaya, Andreas; Kobbelt, Leif; P. Debevec and S. Gibson
We propose a highly efficient hierarchical representation for point sampled geometry that automatically balances sampling density and point coordinate quantization. The representation is very compact with a memory consumption of far less than 2 bits per point position which does not depend on the quantization precision. We present an efficient rendering algorithm that exploits the hierarchical structure of the representation to perform fast 3D transformations and shading. The algorithm is extended to surface splatting which yields high quality anti-aliased and water tight surface renderings. Our pure software implementation renders up to 14 million Phong shaded and textured samples per second and about 4 million anti-aliased surface splats on a commodity PC. This is more than a factor 10 times faster than previous algorithms.
Enhancing and Optimizing the Render Cache
(The Eurographics Association, 2002) Walter, Bruce; Drettakis, George; Greenberg, Donald P.; P. Debevec and S. Gibson
Interactive rendering often requires the use of simplified shading algorithms with reduced illumination fidelity. Higher quality rendering algorithms are usually too slow for interactive use. The render cache is a technique to bridge this performance gap and allow ray-based renderers to be used in interactive contexts by providing automatic sample interpolation, frame-to-frame sample reuse, and prioritized sampling. In this paper we present several extensions to the original render cache including predictive sampling, reorganized computation for better memory coherence, an additional interpolation filter to handle sparser data, and SIMD acceleration. These optimizations allow the render cache to scale to larger resolutions, reduce its visual artifacts, and provide better handling of low sample rates. We also provide a downloadable binary to allow researchers to evaluate and use the render cache.
Exact From-Region Visibility Culling
(The Eurographics Association, 2002) Nirenstein, S.; Blake, E.; Gain, J.; P. Debevec and S. Gibson
To pre-process a scene for the purpose of visibility culling during walkthroughs it is necessary to solve visibility from all the elements of a finite partition of viewpoint space. Many conservative and approximate solutions have been developed that solve for visibility rapidly. The idealised exact solution for general 3D scenes has often been regarded as computationally intractable. Our exact algorithm for finding the visible polygons in a scene from a region is a computationally tractable pre-process that can handle scenes of the order of millions of polygons. The essence of our idea is to represent 3-D polygons and the stabbing lines connecting them in a 5-D Euclidean space derived from Plücker space and then to perform geometric subtractions of occluded lines from the set of potential stabbing lines.We have built a query architecture around this query algorithm that allows for its practical application to large scenes. We have tested the algorithm on two different types of scene: despite a large constant computational overhead, it is highly scalable, with a time dependency close to linear in the output produced.
Fast Primitive Distribution for Illustration
(The Eurographics Association, 2002) Secord, Adrian; Heidrich, Wolfgang; Streit, Lisa; P. Debevec and S. Gibson
In this paper we present a high-quality, image-space approach to illustration that preserves continuous tone by probabilistically distributing primitives while maintaining interactive rates. Our method allows for frame-to-frame coherence by matching movements of primitives with changes in the input image. It can be used to create a variety of drawing styles by varying the primitive type or direction. We show that our approach is able to both preserve tone and (depending on the drawing style) high-frequency detail. Finally, while our algorithm requires only an image as input, additional 3D information enables the creation of a larger variety of drawing styles.
Fast, Arbitrary BRDF Shading for Low-Frequency Lighting Using Spherical Harmonics
(The Eurographics Association, 2002) Kautz, Jan; Sloan, Peter-Pike; Snyder, John; P. Debevec and S. Gibson
Real-time shading using general (e.g., anisotropic) BRDFs has so far been limited to a few point or directional light sources. We extend such shading to smooth, area lighting using a low-order spherical harmonic basis for the lighting environment. We represent the 4D product function of BRDF times the cosine factor (dot product of the incident lighting and surface normal vectors) as a 2D table of spherical harmonic coefficients. Each table entry represents, for a single view direction, the integral of this product function times lighting on the hemisphere expressed in spherical harmonics. This reduces the shading integral to a simple dot product of 25 component vectors, easily evaluatable on PC graphics hardware. Non-trivial BRDF models require rotating the lighting coefficients to a local frame at each point on an object, currently forming the computational bottleneck. Real-time results can be achieved by fixing the view to allow dynamic lighting or vice versa. We also generalize a previous method for precomputed radiance transfer to handle general BRDF shading. This provides shadows and interreflections that respond in real-time to lighting changes on a preprocessed object of arbitrary material (BRDF) type.
The Free-form Light Stage
(The Eurographics Association, 2002) Masselus, Vincent; Dutré, Philip; Anrys, Frederik; P. Debevec and S. Gibson
We present the Free-form Light Stage, a system that captures the reflectance field of an object using a free-moving, hand-held light source. By photographing the object under different illumination conditions, we are able to render the object under any lighting condition, using a linear combination of basis images. During the data acquisition, the light source is moved freely around the object and hence, for each picture, the illuminant direction is unknown. This direction is estimated automatically from the images. Although the reflectance field is sampled non-uniformly, appropriate weighting coefficients are calculated. Using this system, we are able to relight objects in a convincing and realistic way.
GigaWalk: Interactive Walkthrough of Complex Environments
(The Eurographics Association, 2002) III, William V. Baxter; Sud, Avneesh; Govindaraju, Naga K.; Manocha, Dinesh; P. Debevec and S. Gibson
We present a new parallel algorithm and a system, GigaWalk, for interactive walkthrough of complex, gigabytesized environments. Our approach combines occlusion culling and levels-of-detail and uses two graphics pipelines with one or more processors. GigaWalk uses a unified scene graph representation for multiple acceleration techniques, and performs spatial clustering of geometry, conservative occlusion culling, and load-balancing between graphics pipelines and processors. GigaWalk has been used to render CAD environments composed of tens of millions of polygons at interactive rates on systems consisting of two graphics pipelines. Overall, our system s combination of levels-of-detail and occlusion culling techniques results in significant improvements in frame-rate over view-frustum culling or either single technique alone.
Hardware-Accelerated Point-Based Rendering of Complex Scenes
(The Eurographics Association, 2002) Coconu, Liviu; Hege, Hans-Christian; P. Debevec and S. Gibson
High quality point rendering methods have been developed in the last years. A common drawback of these approaches is the lack of hardware support. We propose a novel point rendering technique that yields good image quality while fully making use of hardware acceleration. Previous research revealed various advantages and drawbacks of point rendering over traditional rendering. Thus, a guideline in our algorithm design has been to allow both primitive types simultaneously and dynamically choose the best suited for rendering. An octree-based spatial representation, containing both triangles and sampled points, is used for level-of-detail and visibility calculations. Points in each block are stored in a generalized layered depth image. McMillan s algorithm is extended and hierarchically applied in the octree to warp overlapping Gaussian fuzzy splats in occlusion-compatible order and hence z-buffer tests are avoided. We show how to use off-the-shelf hardware to draw elliptical Gaussian splats oriented according to normals and to perform texture filtering. The result is a hybrid polygon-point system with increased efficiency compared to previous approaches.
Image-based Environment Matting
(The Eurographics Association, 2002) Wexler, Yonatan; Fitzgibbon, Andrew. W.; Zisserman, Andrew.; P. Debevec and S. Gibson
Environment matting is a powerful technique for modeling the complex light-transport properties of real-world optically active elements: transparent, refractive and reflective objects. Recent research has shown how environment mattes can be computed for real objects under carefully controlled laboratory conditions. However, many objects for which environment mattes are necessary for accurate rendering cannot be placed into a calibrated lighting environment. We show in this paper that analysis of the way in which optical elements distort the appearance of their backgrounds allows the construction of environment mattes in situ without the need for specialized calibration. Specifically, given multiple images of the same element over the same background, where the element and background have relative motion, it is shown that both the background and the optical element s light-transport path can be computed. We demonstrate the technique on two different examples. In the first case, the optical element s geometry is simple, and evaluation of the realism of the output is easy. In the second, previous techniques would be difficult to apply. We show that image-based environment matting yields a realistic solution. We discuss how the stability of the solution depends on the number of images used, and how to regularize the solution where only a small number of images are available
Interactive Global Illumination using Fast Ray Tracing
(The Eurographics Association, 2002) Wald, Ingo; Kollig, Thomas; Benthin, Carsten; Keller, Alexander; Slusallek, Philipp; P. Debevec and S. Gibson
Rasterization hardware provides interactive frame rates for rendering dynamic scenes, but lacks the ability of ray tracing required for efficient global illumination simulation. Existing ray tracing based methods yield high quality renderings but are far too slow for interactive use. We present a new parallel global illumination algorithm that perfectly scales, has minimal preprocessing and communication overhead, applies highly efficient sampling techniques based on randomized quasi-Monte Carlo integration, and benefits from a fast parallel ray tracing implementation by shooting coherent groups of rays. Thus a performance is achieved that allows for applying arbitrary changes to the scene, while simulating global illumination including shadows from area light sources, indirect illumination, specular effects, and caustics at interactive frame rates. Ceasing interaction rapidly provides high quality renderings.
Interactive Global Illumination Using Selective Photon Tracing
(The Eurographics Association, 2002) Dmitriev, Kirill; Brabec, Stefan; Myszkowski, Karol; Seidel, Hans-Peter; P. Debevec and S. Gibson
We present a method for interactive global illumination computation which is embedded in the framework of Quasi-Monte Carlo photon tracing and density estimation techniques. The method exploits temporal coherence of illumination by tracing photons selectively to the scene regions that require illumination update. Such regions are identified with a high probability by a small number of the pilot photons. Based on the pilot photons which require updating, the remaining photons with similar paths in the scene can be found immediately. This becomes possible due to the periodicity property inherent to the multi-dimensional Halton sequence, which is used to generate photons. If invalid photons cannot all be updated during a single frame, frames are progressively refined in subsequent cycles. The order in which the photons are updated is decided by inexpensive energy- and perception-based criteria whose goal is to minimize the perceivability of outdated illumination. The method buckets all photons on-the-fly in mesh elements and does not require any data structures in the temporal domain, which makes it suitable for interactive rendering of complex scenes. Since mesh-based reconstruction of lighting patterns with high spatial frequencies is inefficient, we use a hybrid approach in which direct illumination and resulting shadows are rendered using graphics hardware.
Local Illumination Environments for Direct Lighting Acceleration
(The Eurographics Association, 2002) Fernandez, Sebastian; Bala, Kavita; Greenberg, Donald P.; P. Debevec and S. Gibson
Computing high-quality direct illumination in scenes with many lights is an open area of research. This paper presents a world-space caching mechanism called local illumination environments that enables interactive direct illumination in complex scenes on a cluster of off-the-shelf PCs. A local illumination environment (LIE) caches geometric and radiometric information related to direct illumination. A LIE is associated with every octree cell constructed over the scene. Each LIE stores a set of visible lights, with associated occluders (if they exist). LIEs are effective at accelerating direct illumination because they both eliminate shadow rays for fully visible and fully occluded regions of the scene, and decrease the cost of shadow rays in other regions. Shadow ray computation for the partially occluded regions is accelerated using the cached potential occluders. One important implication of storing occluders is that rendering is accelerated while producing accurate hard and soft shadows. This paper also describes a simple perceptual metric based on Weber s law that further improves the effectiveness of LIEs in the fully visible and partially occluded regions. LIE construction is view-driven, continuously refined, and asynchronous with the shading process. In complex scenes of hundreds of thousands of polygons with up to a hundred lights, the LIEs improve rendering performance by 10x to 30x over a traditional ray tracer.
Microfacet Billboarding
(The Eurographics Association, 2002) Yamazaki, Shuntaro; Sagawa, Ryusuke; Kawasaki, Hiroshi; Ikeuchi, Katsushi; Sakauchi, Masao; P. Debevec and S. Gibson
Rendering of intricately shaped objects that are soft or cluttered is difficult because we cannot accurately acquire their complete geometry. Since their geometry varies drastically, modeling them using fixed facets can lead to severe artifacts when viewed from singular directions. In this paper, we propose a novel modeling method, "microfacet billboarding", which uses view-dependent "microfacets" with view-dependent textures. The facets discretely approximate the geometry of the object and are aligned perpendicular to the viewing direction. The texture of each facet is selected from the most suitable texture images according to the viewpoint. Microfacet billboarding can render intricate geometry from various viewpoints. We first describe the basic algorithm of microfacet billboarding. Also, we predict artifacts generated due to the use of discrete facets and we analyze the necessary sampling interval of the geometry and texture for regarding the artifacts as negligible. In addition to the modeling method, we have implemented a real-time renderer by a hardware-accelerated technique. To evaluate the efficiency of our method, we compared it with traditional texture mapping to a mesh model, and showed that our method has a great advantage over the former in rendering intricately shaped objects.
Picture Perfect RGB Rendering Using Spectral Prefiltering and Sharp Color Primaries
(The Eurographics Association, 2002) Ward, Greg; Eydelberg-Vileshin, Elena; P. Debevec and S. Gibson
Accurate color rendering requires the consideration of many samples over the visible spectrum, and advanced rendering tools developed by the research community offer multispectral sampling towards this goal. However, for practical reasons including efficiency, white balance, and data demands, most commercial rendering packages still employ a naive RGB model in their lighting calculations. This results in colors that are often qualitatively different from the correct ones. In this paper, we demonstrate two independent and complementary techniques for improving RGB rendering accuracy without impacting calculation time: spectral prefiltering and color space selection. Spectral prefiltering is an obvious but overlooked method of preparing input colors for a conventional RGB rendering calculation, which achieves exact results for the direct component, and very accurate results for the interreflected component when compared with full-spectral rendering. In an empirical error analysis of our method, we show how the choice of rendering color space also affects final image accuracy, independent of prefiltering. Specifically, we demonstrate the merits of a particular transform that has emerged from the color research community as the best performer in computing white point adaptation under changing illuminants: the Sharp RGB space.
A Real-Time Distributed Light Field Camera
(The Eurographics Association, 2002) Yang, Jason C.; Everett, Matthew; Buehler, Chris; McMillan, Leonard; P. Debevec and S. Gibson
We present the design and implementation of a real-time, distributed light field camera. Our system allows multiple viewers to navigate virtual cameras in a dynamically changing light field that is captured in real-time. Our light field camera consists of 64 commodity video cameras that are connected to off-the-shelf computers. We employ a distributed rendering algorithm that allows us to overcome the data bandwidth problems inherent in dynamic light fields. Our algorithm works by selectively transmitting only those portions of the video streams that contribute to the desired virtual views. This technique not only reduces the total bandwidth, but it also allows us to scale the number of cameras in our system without increasing network bandwidth. We demonstrate our system with a number of examples.

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