EGSR03: 14th Eurographics Symposium on Rendering

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https://diglib.eg.org/handle/10.2312/382

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Capturing and Rendering With Incident Light Fields
(The Eurographics Association, 2003) Unger, J.; Wenger, A.; Hawkins, T.; Gardner, A.; Debevec, P.; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
This paper presents a process for capturing spatially and directionally varying illumination from a real-world scene and using this lighting to illuminate computer-generated objects. We use two devices for capturing such illumination. In the first we photograph an array of mirrored spheres in high dynamic range to capture the spatially varying illumination. In the second, we obtain higher resolution data by capturing images with an high dynamic range omnidirectional camera as it traverses across a plane. For both methods we apply the light field technique to extrapolate the incident illumination to a volume. We render computer-generated objects as illuminated by this captured illumination using a custom shader within an existing global illumination rendering system. To demonstrate our technique we capture several spatially-varying lighting environments with spotlights, shadows, and dappled lighting and use them to illuminate synthetic scenes. We also show comparisons to real objects under the same illumination.
Computer Generated Celtic Design
(The Eurographics Association, 2003) Kaplan, Matthew; Cohen, Elaine; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
We present a technique for automating the construction of Celtic knotwork and decorations similar to those in illuminated manuscripts such as the Lindisfarne Gospels. Our method eliminates restrictions imposed by previous methods which limited the class of knots that could be produced correctly by introducing new methods for smoothing and orienting threads. Additionally, we present techniques for interweaving and attaching images to the knotwork and techniques to encapsulate knot patterns to simplify the design process. Finally we show how to use such knotwork in 3D and demonstrate a variety of applications including artwork and transforming the designs into 3D models for fabrication.
Delivering Interactivity to Complex Tone Mapping Operators
(The Eurographics Association, 2003) Artusi, Alessandro; Bittner, Jirí; Wimmer, Michael; Wilkie, Alexander; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
The accurate display of high dynamic range images requires the application of complex tone mapping operators. These operators are computationally costly, which prevents their usage in interactive applications. We propose a general framework that delivers interactive performance to an important subclass of tone mapping operators, namely global tone mapping operators. The proposed framework consists of four steps: sampling the input image, applying the tone mapping operator, fitting the point-sampled tone mapping curve, and reconstructing the tone mapping curve for all pixels of the input image. We show how to make use of recent graphics hardware while keeping the advantage of generality by performing tone mapping in software. We demonstrate the capabilities of our method by accelerating several common global tone mapping operators and integrating the operators in a real-time rendering application.
Detail to Attention: Exploiting Visual Tasks for Selective Rendering
(The Eurographics Association, 2003) Cater, K.; Chalmers, A.; Ward, G.; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
The perceived quality of computer graphics imagery depends on the accuracy of the rendered frames, as well as the capabilities of the human visual system. Fully detailed, high fidelity frames still take many minutes even hours to render on today's computers. The human eye is physically incapable of capturing a moving scene in full detail. We sense image detail only in a 2± foveal region, relying on rapid eye movements, or saccades, to jump between points of interest. Our brain then reassembles these glimpses into a coherent, but inevitably imperfect, visual percept of the environment. In the process, we literally lose sight of the unimportant details. In this paper, we demonstrate how properties of the human visual system, in particular inattentional blindness, can be exploited to accelerate the rendering of animated sequences by applying a priori knowledge of a viewer's task focus. We show in a controlled experimental setting how human subjects will consistently fail to notice degradations in the quality of image details unrelated to their assigned task, even when these details fall under the viewers' gaze. We then build on these observations to create a perceptual rendering framework that combines predetermined task maps with spatiotemporal contrast sensitivity to guide a progressive animation system which takes full advantage of image-based rendering techniques. We demonstrate this framework with a Radiance ray-tracing implementation that completes its work in a fraction of the normally required time, with few noticeable artifacts for viewers performing the task.
Efficient and Realistic Visualization of Cloth
(The Eurographics Association, 2003) Sattler, Mirko; Sarlette, Ralf; Klein, Reinhard; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
Efficient and realistic rendering of cloth is of great interest especially in the context of e-commerce. Aside from the simulation of cloth draping, the rendering has to provide the "look and feel" of the fabric itself. In this paper we present a novel interactive rendering algorithm to preserve this "look and feel" of different fabrics. This is done by using the bidirectional texture function (BTF) of the fabric, which is acquired from a rectangular probe and after synthesis, mapped onto the simulated geometry. Instead of fitting a special type of bidirectional reflection distribution function (BRDF) model to each texel of our BTF, we generate view-dependent texture-maps using a principal component analysis of the original data. These view-dependent texture maps are then illuminated and rendered using either point-light sources or high dynamic range environment maps by exploiting current graphics hardware. In both cases, self-shadowing caused by geometry is taken into account. For point light sources, we also present a novel method to generate smooth shadow boundaries on the geometry. Depending on the geometrical complexity and the sampling density of the environment map, the illumination can be changed interactively. To ensure interactive frame rates for denser samplings or more complex objects, we introduce a principal component based decomposition of the illumination of the geometry. The high quality of the results is demonstrated by several examples. The algorithm is also suitable for materials other than cloth, as far as these materials have a similar reflectance behavior.
Efficient Illumination by High Dynamic Range Images
(The Eurographics Association, 2003) Kollig, Thomas; Keller, Alexander; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
We present an algorithm for determining quadrature rules for computing the direct illumination of predominantly diffuse objects by high dynamic range images. The new method precisely reproduces fine shadow detail, is much more efficient as compared to Monte Carlo integration, and does not require any manual intervention.
Efficient Isotropic BRDF Measurement
(The Eurographics Association, 2003) Matusik, Wojciech; Pfister, Hanspeter; Brand, Matthew; McMillan, Leonard; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
In this paper we present novel reflectance measurement procedures that require fewer total measurements than standard uniform sampling approaches. First, we acquire densely sampled reflectance data for a large collection of different materials. Using these densely sampled measurements we analyze the general surface reflectance function to determine the local signal variation at each point in the function's domain. We then use wavelet analysis to derive a common basis for all of the acquired reflectance functions as well as a corresponding non-uniform sampling pattern that corresponds to all non-zero wavelet coefficients. Second, we show that the reflectance of an arbitrary material can be represented as a linear combination of the surface reflectance functions. Furthermore, our analysis provides a reduced set of sampling points that permits us to robustly estimate the coefficients of this linear combination. These procedures dramatically shorten the acquisition time for isotropic reflectance measurements. We present a detailed description and analysis of our measurement approaches and sampling strategies.
An Efficient Spatio-Temporal Architecture for Animation Rendering
(The Eurographics Association, 2003) Havran, Vlastimil; Damez, Cyrille; Myszkowski, Karol; Seidel, Hans-Peter; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
Producing high quality animations featuring rich object appearance and compelling lighting effects is very time consuming using traditional frame-by-frame rendering systems. In this paper we present a rendering architecture for computing multiple frames at once by exploiting the coherencebetween image samples in the temporal domain. For each sample representing a given point in the scene we update its view-dependent components for each frame and add its contribution to pixels identified through the compensation of camera and object motion. This leads naturally to a high quality motion blur and significantly reduces the cost of illumination computations. The required visibility information is provided using a custom ray tracing acceleration data structure for multiple frames simultaneously. We demonstrate that precise and costly global illumination techniques such as bidirectional path tracing become affordable in this rendering architecture.
Erosion Based Visibility Preprocessing
(The Eurographics Association, 2003) Décoret, Xavier; Debunne, Gilles; Sillion, François; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
This paper presents a novel method for computing visibility in 2.5D environments based on a novel theoretical result: the visibility from a region can be conservatively estimated by computing the visibility from a point using appropriately "shrunk" occluders and occludees. We show how approximate, yet conservative, shrunk objects can be efficiently computed in an urban environment. The technique provides a tighter potentially visible set (PVS) compared to the original method in which only occluders are shrunk. Finally, theoretical implications of the shrinking theorem are discussed, opening new research directions.
Fast Texture Synthesis on Arbitrary Meshes
(The Eurographics Association, 2003) Magda, Sebastian; Kriegman, David; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
While texture synthesis on surfaces has received much attention in computer graphics, the ideal solution that quickly produces high-quality textures with little user intervention has remained elusive. The algorithm presented in this paper brings us closer to that goal by generating high-quality textures on arbitrary meshes in a matter of seconds. It achieves that by separating texture preprocessing from texture synthesis and accelerating the candidate search process. The result of this is a mapping of every triangle in a mesh to the original texture sample with no need for additional texture memory. The whole process is fully automatic, yet still user controllable. It also places no special restrictions on the mesh or on the texture, and the original mesh is not modified in any way. A preprocessed texture sample can be used to synthesize a texture map on any number of meshes.
Global Illumination Animation with Random Radiance Representation
(The Eurographics Association, 2003) Szirmay-Kalos, László; Antal, György; Benedek, Balázs; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
This paper proposes a non-diffuse global illumination algorithm that is fast enough to be appropriate for interactive walkthroughs and general animations. To meet the severe performance requirements, we heavily exploit coherence both in time and space, and use randomization to reduce the time and storage complexity. To speed up convergence and to support animation, the approximation of the radiance is stored in object space as well. However, in order to reduce the high memory requirements of such representations and to reduce finite-element artifacts, we use just a random approximation, which fluctuates around the real radiance function. The direction dependent radiance approximation is represented in a compact way, by four random variables per patch. The key of performance is then to make the error, i.e. the variance of this compact approximation as small as possible. In addition to main part separation, we apply a novel sampling scheme inspired by the Metropolis method to achieve this goal. In this algorithm light transfers are computed by both local and global methods using ray bundles and with the support of the graphics hardware. We conclude that both local and global approaches fail to efficiently compute all types of transfers, thus cannot be used alone. However, with the aid of multiple importance sampling, the merits of the two light transfer methods can be combined resulting in an algorithm that is robust and fast enough for animations. On the other hand, ray bundles, especially global ones, can update the illumination quickly when objects move, since they can efficiently identify which light paths became invalid.
Hybrid Texture Synthesis
(The Eurographics Association, 2003) Nealen, Andrew; Alexa, Marc; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
Patch-based texture synthesis algorithms produce reasonable results for a wide variety of texture classes. They preserve global structure, but often introduce unwanted visual artifacts along patch boundaries. Pixel-based synthesis algorithms, on the other hand, tend to blur out small objects while maintaining a consistent texture impression, which in return doesn t necessarily resemble the input texture. In this paper, we propose an adaptive and hybrid algorithm. Our algorithm adaptively splits patches so as to use as large as possible patches while staying within a user-defined error tolerance for the mismatch in the overlap region. Using large patches improves the reproduction of global structure. The remaining errors in the overlap regions are eliminated using pixel-based re-synthesis. We introduce an optimized ordering for the re-synthesis of these erroneous pixels using morphological operators, which ensures that every pixel has enough valid (i.e., error-free) neighboring pixels. Examples and comparisons with existing techniques demonstrate that our approach improves over previous texture synthesis algorithms, especially for textures with well-visible, possibly anisotropic structure, such as natural stone wall or scales.
Interactive Global Illumination in Complex and Highly Occluded Environments
(The Eurographics Association, 2003) Wald, Ingo; Benthin, Carsten; Slusallek, Philipp; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
Global illumination algorithms have traditionally been very time consuming and were only suitable for off-line computations. Recent research in realtime ray tracing has improved global illumination performance to allow for illumination updates at interactive rates. However, both the traditional off-line and the new interactive systems show significant limitations when dealing with realistically complex scenes containing millions of surfaces, thousands of light sources, and a high degree of occlusion. In this paper, we present an importance sampling technique that has specifically been designed for such environments. Our method maintains a rough estimate of the importance of each light source with respect to the current view using a crude path tracing step. This estimate is then used to focus computations to the most important light sources. In addition to speeding up the computation our approach minimizes the working set of the ray tracer by only touching geometry that is relevant to the current view. This allows us to directly and efficiently render scenes such as entire buildings with many thousands of light sources at interactive rates with full global illumination.
Interactive Rendering of Translucent Deformable Objects
(The Eurographics Association, 2003) Mertens, Tom; Kautz, Jan; Bekaert, Philippe; Seidel, Hans-Peter; Reeth, Frank Van; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
Realistic rendering of materials such as milk, fruits, wax, marble, and so on, requires the simulation of subsurface scattering of light. This paper presents an algorithm for plausible reproduction of subsurface scattering effects. Unlike previously proposed work, our algorithm allows to interactively change lighting, viewpoint, subsurface scattering properties, as well as object geometry. The key idea of our approach is to use a hierarchical boundary element method to solve the integral describing subsurface scattering when using a recently proposed analytical BSSRDF model. Our approach is inspired by hierarchical radiosity with clustering. The success of our approach is in part due to a semi-analytical integration method that allows to compute needed point-to-patch form-factor like transport coefficients efficiently and accurately where other methods fail. Our experiments show that high-quality renderings of translucent objects consisting of tens of thousands of polygons can be obtained from scratch in fractions of a second. An incremental update algorithm further speeds up rendering after material or geometry changes.
Interactive Texture Synthesis on Surfaces Using Jump Maps
(The Eurographics Association, 2003) Zelinka, Steve; Garland, Michael; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
We introduce a new method for fast texture synthesis on surfaces from examples. We generalize the image-based jump map texture synthesis algorithm, which partitions the task of texture synthesis into a slower analysis phase and a fast synthesis phase, by developing a new synthesis phase which works directly on arbitrary surfaces. Our method is one to two orders of magnitude faster than existing techniques, and does not generate any new texture images, enabling interactive applications for reasonably-sized meshes. This capability would be useful in many areas, including the texturing of dynamically-generated surfaces, interactive modelling applications, and rapid prototyping workflows. Our method remains simple to implement, assigning an offset in texture space to each edge of the mesh, followed by a walk over the mesh vertices to assign texture coordinates. A final step ensures each triangle receives consistent texture coordinates at its corners, and if available, texture blending can be used to improve the quality of results.
Interactive Time-Dependent Tone Mapping Using Programmable Graphics Hardware
(The Eurographics Association, 2003) Goodnight, Nolan; Wang, Rui; Woolley, Cliff; Humphreys, Greg; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
Modern graphics architectures have replaced stages of the graphics pipeline with fully programmable modules. Therefore, it is now possible to perform fairly general computation on each vertex or fragment in a scene. In addition, the nature of the graphics pipeline makes substantial computational power available if the programs have a suitable structure. In this paper, we show that it is possible to cleanly map a state-of-the-art tone mapping algorithm to the pixel processor. This allows an interactive application to achieve higher levels of realism by rendering with physically based, unclamped lighting values and high dynamic range texture maps. We also show that the tone mapping operator can easily be extended to include a time-dependent model, which is crucial for interactive behavior. Finally, we describe the ways in which the graphics hardware limits our ability to compress dynamic range efficiently, and discuss modifications to the algorithm that could alleviate these problems.
A New Reconstruction Filter for Undersampled Light Fields
(The Eurographics Association, 2003) Stewart, J.; Yu, J.; Gortler, S.J.; McMillan, L.; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
This paper builds on previous research in the light field area of image-based rendering. We present a new reconstruction filter that significantly reduces the "ghosting" artifacts seen in undersampled light fields, while preserving important high-fidelity features such as sharp object boundaries and view-dependent reflectance. By improving the rendering quality achievable from undersampled light fields, our method allows acceptable images to be generated from smaller image sets. We present both frequency and spatial domain justifications for our techniques. We also present a practical framework for implementing the reconstruction filter in multiple rendering passes.
Optimizing Color Matching in a Lighting Reproduction System for Complex Subject and Illuminant Spectra
(The Eurographics Association, 2003) Wenger, A.; Hawkins, T.; Debevec, P.; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
This paper presents a technique for improving color matching results in an LED-based lighting reproduction system for complex light source spectra. In our technique, we use measurements of the spectral response curve of the camera system as well as one or more spectral reflectance measurements of the illuminated object to optimize the color matching. We demonstrate our technique using two LED-based light sources: an off-the-shelf 3-channel RGB LED light source and a custom-built 9-channel multi-spectral LED light source. We use our technique to reproduce complex lighting spectra including both fluorescent and tungsten illumination using a Macbeth color checker chart and a human face as test subjects. We show that by using knowledge of the camera spectral response and/or the spectral reflectance of the subjects that we can significantly improve the accuracy of the color matching using either the 3-channel or the 9-channel light, achieving acceptable matches for the 3-channel source and very close matches for the multi-spectral 9-channel source.
Path Integration for Light Transport in Volumes
(The Eurographics Association, 2003) Premoze, Simon; Ashikhmin, Michael; Shirley, Peter; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
Simulating the transport of light in volumes such as clouds or objects with subsurface scattering is computationally expensive. We describe an approximation to such transport using path integration. Unlike the more commonly used diffusion approximation, the path integration approach does not explicitly rely on the assumption that the material within the volume is dense. Instead, it assumes the phase function of the volume material is strongly forward scattering and uniform throughout the medium, an assumption that is often the case in nature. We show that this approach is useful for simulating subsurface scattering and scattering in clouds.
Penumbra Maps: Approximate Soft Shadows in Real-Time
(The Eurographics Association, 2003) Wyman, Chris; Hansen, Charles; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
Generating soft shadows quickly is difficult. Few techniques have enough flexibility to interactively render soft shadows in scenes with arbitrarily complex occluders and receivers. This paper introduces the penumbra map, which extends current shadow map techniques to interactively approximate soft shadows. Using object silhouette edges, as seen from the center of an area light, a map is generated containing approximate penumbral regions. Rendering requires two lookups, one into each the penumbra and shadow maps. Penumbra maps allow arbitrary dynamic models to easily shadow themselves and other nearby complex objects with plausible penumbrae.

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