2001_EGWR01: 12th Eurographics Workshop on Rendering

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https://diglib.eg.org/handle/10.2312/380

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Point-Based Impostors for Real-Time Visualization
(The Eurographics Association, 2001) Wimmer, Michael; Wonka, Peter; Sillion, Francois; S. J. Gortle and K. Myszkowski
We present a new data structure for encoding the appearance of a geometric model as seen from a viewing region (view cell). This representation can be used in interactive or real-time visualization applications to replace a complex model by an impostor, maintaining high quality rendering while cutting down rendering time. Our approach relies on an object-space sampled representation similar to a point cloud or a layered depth image, but introduces two fundamental additions to previous techniques. First, the sampling rate is controlled to provide sufficient density across all possible viewing conditions from the specified view cell. Second, a correct, antialiased representation of the plenoptic function is computed using Monte Carlo integration. Our system therefore achieves high quality rendering using a simple representation with bounded complexity. We demonstrate the method for an application in urban visualization.
TheWavelet Stream: Interactive Multi Resolution Light Field Rendering
(The Eurographics Association, 2001) Peter, Ingmar; Straßer, Wolfgang; S. J. Gortle and K. Myszkowski
One of the most general image based object representations is the Light Field. Unfortunately, a large amount of data is required to reconstruct high quality views from a Light Field. In this paper, we present the wavelet stream which employs non-standard four-dimensional wavelet decomposition for Light Field compression. It allows for progressive transmission, storage, and rendering of compressed Light Field data. Our results show that 0.8% of the original coefficients or 0.3 bits per pixel, respectively are sufficient to obtain visually pleasing new views. Additionally, the wavelet stream allows for an adaptive multi-resolution representation of the Light Field data. Furthermore, a silhouetteencoding scheme helps to reduce the number of coefficients required. Our data structure allows to store arbitrary vector-valued data like RGB- or YUV-data. The Light Field data stored in the wavelet stream can be decompressed in real time for interactive rendering. For this, the reconstruction algorithm uses supplementary caching schemes.
Real-Time Occlusion Culling with a Lazy Occlusion Grid
(The Eurographics Association, 2001) Hey, Heinrich; Tobler, Robert F.; Purgathofer, Werner; S. J. Gortle and K. Myszkowski
We present a new conservative image-space occlusion culling method to increase the rendering speed of very large general scenes on today's available hardware without time-expensive preprocessing. The method is based on a low-resolution grid upon a conventional z-buffer. The occlusion information in the grid is updated in a lazy manner. In comparison to related methods this significantly reduces the number of pixels that have to be read from the z-buffer. The grid allows fast decisions if an object is occluded or potentially visible. It is used together with a bounding volume hierarchy that is traversed in a front-to-back order and which allows to cull large parts of the scene at once. A special front-to-back traversal is used if no pixel-level query for the furthest z-value of an image area is available. We show that the method works efficiently on today's available hardware and we compare it with related methods.
Polyhedral Visual Hulls for Real-Time Rendering
(The Eurographics Association, 2001) Matusik, Wojciech; Buehler, Chris; McMillan, Leonard; S. J. Gortle and K. Myszkowski
We present new algorithms for creating and rendering visual hulls in real-time. Unlike voxel or sampled approaches, we compute an exact polyhedral representation for the visual hull directly from the silhouettes. This representation has a number of advantages: 1) it is a view-independent representation, 2) it is well-suited to rendering with graphics hardware, and 3) it can be computed very quickly. We render these visual hulls with a view-dependent texturing strategy, which takes into account visibility information that is computed during the creation of the visual hull. We demonstrate these algorithms in a system that asynchronously renders dynamically created visual hulls in real-time. Our system outperforms similar systems of comparable computational power.
Efficient Cloth Modeling and Rendering
(The Eurographics Association, 2001) Daubert, Katja; Lensch, Hendrik P. A.; Heidrich, Wolfgang; Seidel, Hans-Peter; S. J. Gortle and K. Myszkowski
Realistic modeling and high-performance rendering of cloth and clothing is a challenging problem. Often these materials are seen at distances where individual stitches and knits can be made out and need to be accounted for. Modeling of the geometry at this level of detail fails due to sheer complexity, while simple texture mapping techniques do not produce the desired quality. In this paper, we describe an efficient and realistic approach that takes into account view-dependent effects such as small displacements causing occlusion and shadows, as well as illumination effects. The method is efficient in terms of memory consumption, and uses a combination of hardware and software rendering to achieve high performance. It is conceivable that future graphics hardware will be flexible enough for full hardware rendering of the proposed method.
Image-Based Reconstruction of Spatially Varying Materials
(The Eurographics Association, 2001) Lensch, Hendrik P. A.; Kautz, Jan; Goesele, Michael; Heidrich, Wolfgang; Seidel, Hans-Peter; S. J. Gortle and K. Myszkowski
The measurement of accurate material properties is an important step towards photorealistic rendering. Many real-world objects are composed of a number of materials that often show subtle changes even within a single material. Thus, for photorealistic rendering both the general surface properties as well as the spatially varying effects of the object are needed. We present an image-based measuring method that robustly detects the different materials of real objects and fits an average bidirectional reflectance distribution function (BRDF) to each of them. In order to model the local changes as well, we project the measured data for each surface point into a basis formed by the recovered BRDFs leading to a truly spatially varying BRDF representation. A high quality model of a real object can be generated with relatively few input data. The generated model allows for rendering under arbitrary viewing and lighting conditions and realistically reproduces the appearance of the original object.
Thrifty Final Gather for Radiosity
(The Eurographics Association, 2001) Scheel, Annette; Stamminger, Marc; Seidel, Hans-Peter; S. J. Gortle and K. Myszkowski
Finite Element methods are well suited to the computation of the light distribution in mostly diffuse scenes, but the resulting mesh is often far from optimal to accurately represent illumination. Shadow boundaries are hard to capture in the mesh, and the illumination may contain artifacts due to light transports at different mesh hierarchy levels. To render a high quality image a costly final gather reconstruction step is usually done, which re-evaluates the illumination integral for each pixel. In this paper an algorithm is presented which significantly speeds up the final gather by exploiting spatial and directional coherence information taken from the radiosity solution. Senders are classified, so that their contribution to a pixel is either interpolated from the radiosity solution or recomputed with an appropriate number of new samples. By interpolating this sampling pattern over the radiosity mesh, continuous solutions are obtained.
Opacity Shadow Maps
(The Eurographics Association, 2001) Kim, Tae-Yong; Neumann, Ulrich; S. J. Gortle and K. Myszkowski
Opacity shadow maps approximate light transmittance inside a complex volume with a set of planar opacity maps. A volume made of standard primitives (points, lines, and polygons) is sliced and rendered with graphics hardware to each opacity map that stores alpha values instead of traditionally used depth values. The alpha values are sampled in the maps enclosing each primitive point and interpolated for shadow computation. The algorithm is memory efficient and extensively exploits existing graphics hardware. The method is suited for generation of self-shadows in discontinuous volumes with explicit geometry, such as foliage, fur, and hairs. Continuous volumes such as clouds and smoke may also benefit from the approach.
An Illumination Model for a Skin Layer Bounded by Rough Surfaces
(The Eurographics Association, 2001) Stam, Jos; S. J. Gortle and K. Myszkowski
In this paper we present a novel illumination model that takes into account multiple anisotropic scattering in a layer bounded by two rough surfaces. We compute the model by a discrete-ordinate solution of the equation of radiative transfer. This approach is orders of magnitude faster than a Monte Carlo simulation and does not suffer from any noisy artifacts. By fitting low order splines to our results we are able to build analytical shaders. This is highly desirable since animators typically want to texture map the parameters of such a shader for higher realism. We apply our model to the important problem of rendering human skin. Our model does not seem to have appeared before in the optics literature. Most previous models did not handle rough surfaces at the skin s boundary. Also we introduce a simple analytical bidirectional transmittance distribution function (BTDF) for an isotropic rough surface by generalizing the Cook-Torrance model.
Interleaved Sampling
(The Eurographics Association, 2001) Keller, Alexander; Heidrich, Wolfgang; S. J. Gortle and K. Myszkowski
The known sampling methods can roughly be grouped into regular and irregular sampling. While regular sampling can be realized efficiently in graphics hardware, it is prone to inter-pixel aliasing. On the other hand these artifacts can easily be masked by noise using irregular sampling which, however, is more expensive to evaluate as it lacks the high coherence of a regular approach. We bridge this gap by introducing a generalized sampling scheme that smoothly blends between regular and irregular sampling. By interleaving the samples of regular grids in an irregular way, we preserve the high coherence and efficiently reduce inter-pixel aliasing thus significantly improving the rendering quality as compared to previous approaches.
Texture and Shape Synthesis on Surfaces
(The Eurographics Association, 2001) Ying, Lexing; Hertzmann, Aaron; Biermann, Henning; Zorin, Denis; S. J. Gortle and K. Myszkowski
We present a novel method for texture synthesis on surfaces from examples. We consider a very general type of textures, including color, transparency and displacements. Our method synthesizes the texture directly on the surface, rather than synthesizing a texture image and then mapping it to the surface. The synthesized textures have the same qualitative visual appearance as the example texture, and cover the surfaces without the distortion or seams of conventional texture-mapping. We describe two synthesis methods, based on the work of Wei and Levoy and Ashikhmin; our techniques produce similar results, but directly on surfaces.
Combined Rendering of Polarization and Fluorescence Effects
(The Eurographics Association, 2001) Wilkie, Alexander; Tobler, Robert F.; Purgathofer, Werner; S. J. Gortle and K. Myszkowski
We propose a practicable way to include both polarization and fluorescence effects in a rendering system at the same time. Previous research in this direction only demonstrated support for either one of these phenomena; using both effects simultaneously was so far not possible, mainly because the techniques for the treatment of polarized light were complicated and required rendering systems written specifically for this task. The key improvement over previous work is that we use a different, more easily handled formalism for the description of polarization state, which also enables us to include fluorescence effects in a natural fashion. Moreover, all of our proposals are straightforward extensions to a conventional spectral rendering system.
Simulating Non-Lambertian Phenomena Involving Linearly-Varying Luminaires
(The Eurographics Association, 2001) Chen, Min; Arvo, James; S. J. Gortle and K. Myszkowski
We present a new technique for exactly computing glossy reflections and transmissions of polygonal Lambertian luminaires with linearly-varying radiant exitance. To derive the underlying closed-form expressions, we introduce a rational generalization of irradiance tensors and an associated recurrence relation. The generalized tensors allow us to integrate a useful class of rational polynomials over regions of the sphere; this class of rational polynomials can simultaneously account for the linear variation of radiant exitance across a planar luminaire and simple forms of non-Lambertian scattering. Applications include the computation of irradiance at a point, view-dependent reflections from glossy surfaces, and transmissions through glossy surfaces, where the scattering is limited to Phong distributions and the incident illumination is due to linearlyvarying luminaires. In polyhedral environments, the resulting expressions can be exactly evaluated in quadratic time (in the Phong exponent) using dynamic programming or efficiently approximated in linear time using standard numerical quadrature. To illustrate the use of generalized irradiance tensors, we present a greatly simplified derivation of a previously published closed-form expression for the irradiance due to linearly-varying luminaires, and simulate Phong-like scattering effects from such emitters. The validity of our algorithm is demonstrated by comparison with Monte Carlo.
Real-time, Photo-realistic, Physically Based Rendering of Fine Scale Human Skin Structure
(The Eurographics Association, 2001) Haroy, Antonio; Guenterz, Brian; Essay, Irfan; S. J. Gortle and K. Myszkowski
Skin is noticeably bumpy in character, which is clearly visible in close-up shots in a film or game. Methods that rely on simple texture-mapping of faces lack such high frequency shape detail, which makes them look non-realistic. More specifically, this detail is usually ignored in real-time applications, or is drawn in manually by an artist. In this paper, we present techniques for capturing and rendering the fine scale structure of human skin. First, we present a method for creating normal maps of skin with a high degree of accuracy from physical data. We also present techniques inspired by texture synthesis to grow skin normal maps to cover the face. Finally, we demonstrate how such skin models can be rendered in real-time on consumer-end graphics hardware.
Perceptually Driven Simplification for Interactive Rendering
(The Eurographics Association, 2001) Luebke, David; Hallen, Benjamin; S. J. Gortle and K. Myszkowski
We present a framework for accelerating interactive rendering, grounded in psychophysical models of visual perception. This framework is applicable to multiresolution rendering techniques that use a hierarchy of local simplification operations. Our method drives those local operations directly by perceptual metrics; the effect of each simplification on the final image is considered in terms of the contrast the operation will induce in the image and the spatial frequency of the resulting change. A simple and conservative perceptual model determines under what conditions the simplification operation will be perceptible, enabling imperceptible simplification in which operations are performed only when judged imperceptible. Alternatively, simplifications may be ordered according to their perceptibility, providing a principled approach to best-effort rendering. We demonstrate this framework applied to view-dependent polygonal simplification. Our approach addresses many interesting topics in the acceleration of interactive rendering, including imperceptible simplification, silhouette preservation, and gaze-directed rendering.
Realistic Reflections and Refractions on Graphics HardwareWith Hybrid Rendering and Layered Environment Maps
(The Eurographics Association, 2001) Hakura, Ziyad S.; Snyder, John M.; S. J. Gortle and K. Myszkowski
We introduce hybrid rendering, a scheme that dynamically ray traces the local geometry of reflective and refractive objects, but approximates more distant geometry by hardwaresupported environment maps (EMs). To limit computation, we use a greedy ray path shading model that prunes the binary ray tree generated by refractive objects to form just two ray paths. We also restrict ray queries to triangle vertices, but perform adaptive tessellation to shoot additional rays where neighboring ray paths differ sufficiently. By using layered, parameterized EMs that are inferred over a set of viewpoint samples to match ray traced imagery, we accurately handle parallax and view-dependent shading in the environment. We increase robustness of EMs by inferring them simultaneously across multiple viewpoints and including environmental geometry that is occluded from the viewpoint sample but is revealed in nearby viewpoints. We demonstrate realistic shiny and glass objects with a user-controlled viewpoint.
Decoupling Strokes and High-Level Attributes for Interactive Traditional Drawing
(The Eurographics Association, 2001) Durand, Frédo; Ostromoukhov, Victor; Miller, Mathieu; Duranleau, Francois; Dorsey, Julie; S. J. Gortle and K. Myszkowski
We present an interactive system, which allows the user to produce drawings in a variety of traditional styles. It takes as input an image and performs semi-automatic tonal modeling. Our system shifts tedious technical aspects to the computer side, while providing the user with freedom on the creative and aesthetic side. The user has low-level control over stroke placement, and high-level control over the tone, smudging and amount of detail. The drawing is rendered in real-time. The basic component is a thresholding model of strokes that can simulate a large class of styles (e.g. pencil, charcoal, engraving). It provides a controllable simulation of the variation of pencil pressure or stroke thickness traditionally used in tonal modeling. We introduce a novel fast equilibration approach for the resulting thresholding structure. The user can specify smudging and control the amount of detail over each part of the
Interactive Rendering of Trees with Shading and Shadows
(The Eurographics Association, 2001) Meyer, Alexandre; Neyret, Fabrice; Poulin, Pierre; S. J. Gortle and K. Myszkowski
The goal of this paper is the interactive rendering of 3D trees covering a landscape, with shading and shadows consistent with the lighting conditions. We propose a new IBR representation, consisting of a hierarchy of Bidirectional Textures, which resemble 6D lightfields. A hierarchy of visibility cube-maps is associated to this representation to improve the performance of shadow calculations. An example of hierarchy for a given tree can be a small branch plus its leaves (or needles), a larger branch, and the entire tree. A Bidirectional Texture (BT) provides a billboard image of a shaded object for each pair of view and light directions. We associate a BT for each level of the hierarchy. When rendering, the appropriate level of detail is selected depending on the distance of the tree from the viewpoint. The illumination reaching each level is evaluated using a visibility cube-map. Thus, we very efficiently obtain the shaded rendering of a tree with shadows without loosing details, contrary to mesh simplification methods. We achieved 7 to 20 fps fly-throughs of a scene with 1000 trees.
Interactive Distributed Ray Tracing of Highly Complex Models
(The Eurographics Association, 2001) Wald, Ingo; Slusallek, Philipp; Benthin, Carsten; S. J. Gortle and K. Myszkowski
Many disciplines must handle the creation, visualization, and manipulation of huge and complex 3D environments. Examples include large structural and mechanical engineering projects dealing with entire cars, ships, buildings, and processing plants. The complexity of such models is usually far beyond the interactive rendering capabilities of todays 3D graphics hardware. Previous approaches relied on costly preprocessing for reducing the number of polygons that need to be rendered per frame but suffered from excessive precomputation times often several days or even weeks. In this paper we show that using a highly optimized software ray tracer we are able to achieve interactive rendering performance for models up to 50 million triangles including reflection and shadow computations. The necessary preprocessing has been greatly simplified and accelerated by more than two orders of magnitude. Interactivity is achieved with a novel approach to distributed rendering based on coherent ray tracing. A single copy of the scene database is used together with caching of BSP voxels in the ray tracing clients.
Shader Lamps: Animating Real Objects With Image-Based Illumination
(The Eurographics Association, 2001) Raskar, Ramesh; Welch, Greg; Low, Kok-Lim; Bandyopadhyay, Deepak; S. J. Gortle and K. Myszkowski
We describe a new paradigm for three-dimensional computer graphics, using projectors to graphically animate physical objects in the real world. The idea is to replace a physical object with its inherent color, texture, and material properties with a neutral object and projected imagery, reproducing the original (or alternative) appearance directly on the object. Because the approach is to effectively lift the visual properties of the object into the projector, we call the projectors shader lamps. We address the central issue of complete and continuous illumination of non-trivial physical objects using multiple projectors and present a set of new techniques that makes the process of illumination practical. We demonstrate the viability of these techniques through a variety of table-top applications, and describe preliminary results to reproduce life-sized virtual spaces.

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