EGSR03: 14th Eurographics Symposium on Rendering

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

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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.
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 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.
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.
Refinement Criteria Based on f-Divergences
(The Eurographics Association, 2003) Rigau, Jaume; Feixas, Miquel; Sbert, Mateu; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
In several domains a refinement criterion is often needed to decide whether to go on or to stop sampling a signal. When the sampled values are homogeneous enough, we assume that they represent the signal fairly well and we do not need further refinement, otherwise more samples are required, possibly with adaptive subdivision of the domain. For this purpose, a criterion which is very sensitive to variability is necessary. In this paper we present a family of discrimination measures, the f-divergences, meeting this requirement. These functions have been well studied and successfully applied to image processing and several areas of engineering. Two applications to global illumination are shown: oracles for hierarchical radiosity and criteria for adaptive refinement in ray-tracing. We obtain significantly better results than with classic criteria, showing that f-divergences are worth further investigation in computer graphics.
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.
Translucent Shadow Maps
(The Eurographics Association, 2003) Dachsbacher, Carsten; Stamminger, Marc; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
Shadow maps are a very efficient means to add shadows to arbitrary scenes. In this paper, we introduce Translucent Shadow Maps, an extension to shadow maps which allows very efficient rendering of sub-surface scattering. Translucent Shadow Maps contain depth and incident light information. Sub-surface scattering is computed on-the-fly during rendering by filtering the shadow map neighborhood. This filtering is done efficiently using a hierarchical approach. We describe optimizations for an implementation of Translucent Shadow Maps on contemporary graphics hardware, that can render complex translucent objects with varying light and material properties in real-time.
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.
Visualization of woven cloth
(The Eurographics Association, 2003) Adabala, Neeharika; Magnenat-Thalmann, Nadia; Fei, Guangzheng; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
A technique for visualizing clothes is proposed that can handle rendering of complex weave patterns. An industrial standard of weave representation is used to derive the weave pattern and a detailed model of light interaction with the pattern is developed. The proposed visualization technique supports viewing of cloth at various levels of detail, and provides a solution for rendering both back and front surfaces of cloth. The technique works for a wide variation in colors of threads, ranging from a single color for both warps and wefts to several colors of threads, woven into a single fabric. The inhomogeneous nature of transparency of woven materials is also captured. To date no technique for visualizing woven clothes has addressed the problem of visualizing complex weave patterns and therefore the above mentioned features are difficult and often impossible to capture with existing techniques. The capabilities of the proposed approach are demonstrated with rendered examples.
Rapid Shadow Generation in Real-World Lighting Environments
(The Eurographics Association, 2003) Gibson, Simon; Cook, Jon; Howard, Toby; Hubbold, Roger; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
We propose a new algorithm that uses consumer-level graphics hardware to render shadows cast by synthetic objects and a real lighting environment. This has immediate benefit for interactive Augmented Reality applications, where synthetic objects must be accurately merged with real images. We show how soft shadows cast by direct and indirect illumination sources may be generated and composited into a background image at interactive rates. We describe how the sources of light (and hence shadow) affecting each point in an image can be efficiently encoded using a hierarchical shaft-based subdivision of line-space. This subdivision is then used to determine the sources of light that are occluded by synthetic objects, and we show how the contributions from these sources may be removed from a background image using facilities available on modern graphics hardware. A trade-off may be made at runtime between shadow accuracy and rendering cost, converging towards a result that is subjectively similar to that obtained using ray-tracing based differential rendering algorithms. Examples of the proposed technique are given for a variety of different lighting environments, and the visual fidelity of images generated by our algorithm is compared to both real photographs and synthetic images generated using non-real-time techniques.
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.
The Trilateral Filter for High Contrast Images and Meshes
(The Eurographics Association, 2003) Choudhury, Prasun; Tumblin, Jack; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
We present a new, single-pass nonlinear filter for edge-preserving smoothing and visual detail removal for N dimensional signals in computer graphics, image processing and computer vision applications. Built from two modified forms of Tomasi and Manduchi's bilateral filter, the new "trilateral" filter smoothes signals towards a sharply-bounded, piecewise-linear approximation. Unlike bilateral filters or anisotropic diffusion methods that smooth towards piecewise constant solutions, the trilateral filter provides stronger noise reduction and better outlier rejection in high-gradient regions, and it mimics the edge-limited smoothing behavior of shock-forming PDEs by region finding with a fast min-max stack. Yet the trilateral filter requires only one user-set parameter, filters an input signal in a single pass, and does not use an iterative solver as required by most PDE methods. Like the bilateral filter, the trilateral filter easily extends to N-dimensional signals, yet it also offers better performance for many visual applications including appearance-preserving contrast reduction problems for digital photography and denoising polygonal meshes.
A Stained Glass Image Filter
(The Eurographics Association, 2003) Mould, David; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
Medieval stained glass windows are a stylized artform that has not previously been thoroughly treated in the computer graphics literature. In this paper, we present an automated method for transforming an arbitrary image into a stained-glass version of that image. The key issues in designing a stained glass window are the tile boundaries and tile colors. We use erosion and dilation operators to manipulate and smooth an initial region segmentation tiling; we choose tile colors from the palette of heraldic tinctures; and finally, we render a displacement-mapped plane to obtain our final image.
Rendering Time Estimation for Real-Time Rendering
(The Eurographics Association, 2003) Wimmer, Michael; Wonka, Peter; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
This paper addresses the problem of estimating the rendering time for a real-time simulation. We study different factors that contribute to the rendering time in order to develop a framework for rendering time estimation. Given a viewpoint (or view cell) and a list of potentially visible objects, we propose several algorithms that can give reasonable upper limits for the rendering time on consumer hardware. This paper also discusses several implementation issues and design choices that are necessary to make the rendering time predictable. Finally, we lay out two extensions to current rendering hardware which would allow implementing a system with constant frame rates.
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.
Rendering Fake Soft Shadows with Smoothies
(The Eurographics Association, 2003) Chan, Eric; Durand, Fredo; Philip Dutre and Frank Suykens and Per H. Christensen and Daniel Cohen-Or
We present a new method for real-time rendering of shadows in dynamic scenes. Our approach builds on the shadow map algorithm by attaching geometric primitives that we call "smoothies" to the objects' silhouettes. The smoothies give rise to fake shadows that appear qualitatively like soft shadows, without the cost of densely sampling an area light source. The soft shadow edges hide objectionable aliasing artifacts that are noticeable with ordinary shadow maps. Our algorithm computes shadows efficiently in image space and maps well to programmable graphics hardware. We present results from several example scenes rendered in real-time.
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.
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.
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.
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.

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