2001_EGWR01: 12th Eurographics Workshop on Rendering

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

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Artistic Composition for Image Creation
(The Eurographics Association, 2001) Gooch, Bruce; Reinhard, Erik; Moulding, Chris; Shirley, Peter; S. J. Gortle and K. Myszkowski
Altering the viewing parameters of a 3D object results in computer graphics images of varying quality. One aspect of image quality is the composition of the image. While the esthetic properties of an image are subjective, some heuristics used by artists to create images can be approximated quantitatively. We present an algorithm based on heuristic compositional rules for finding the format, viewpoint, and layout for an image of a 3D object. Our system computes viewing parameters automatically or allows a user to explicitly manipulate them.
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.
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
Differential Point Rendering
(The Eurographics Association, 2001) Kalaiah, Aravind; Varshney, Amitabh; S. J. Gortle and K. Myszkowski
We present a novel point rendering primitive, called Differential Point (DP), that captures the local differential geometry in the vicinity of a sampled point. This is a more general point representation that, for the cost of a few additional bytes, packs much more information per point than the traditional point-based models. This information is used to efficiently render the surface as a collection of local neighborhoods. The advantages to this representation are manyfold: (1) it delivers a significant reduction in the number of point primitives that represent a surface (2) it achieves robust hardware accelerated per-pixel shading even with no connectivity information (3) it offers a novel point-based simplification technique that has a convenient and intuitive interface for the user to efficiently resolve the speed versus quality tradeoff. The number of primitives being equal, DPs produce a much better quality of rendering than a pure splatbased approach. Visual appearances being similar, DPs are about two times faster and require about 75% less disk space in comparison to splatting primitives.
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.
Hardware-accelerated from-region visibility using a dual ray space
(The Eurographics Association, 2001) Koltun, Vladlen; Chrysanthou, Yiorgos; Cohen-Or, Daniel; S. J. Gortle and K. Myszkowski
In this paper a novel from-region visibility algorithm is described. Its unique properties allow conducting remote walkthroughs in very large virtual environments, without preprocessing and storing prohibitive amounts of visibility information. The algorithm retains its speed and accuracy even when applied to large viewcells. This allows computing from-region visibility on-line, thus eliminating the need for visibility preprocessing. The algorithm utilizes a geometric transform, representing visibility in a two-dimensional space, the dual ray space. Standard rendering hardware is then used for rapidly performing visibility computation. The algorithm is robust and easy to implement, and can trade off between accuracy and speed. We report results from extensive experiments that were conducted on a virtual environment that accurately depicts 160 square kilometers of the city of London.
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.
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.
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.
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 Sampling and Rendering for Complex and Procedural Geometry
(The Eurographics Association, 2001) Stamminger, Marc; Drettakis, George; S. J. Gortle and K. Myszkowski
We present a new sampling method for procedural and complex geometries, which allows interactive point-based modeling and rendering of such scenes. For a variety of scenes, object-space point sets can be generated rapidly, resulting in a sufficiently dense sampling of the final image. We present an integrated approach that exploits the simplicity of the point primitive. For procedural objects a hierarchical sampling scheme is presented that adapts sample densities locally according to the projected size in the image. Dynamic procedural objects and interactive user manipulation thus become possible. The same scheme is also applied to on-the-fly generation and rendering of terrains, and enables the use of an efficient occlusion culling algorithm. Furthermore, by using points the system enables interactive rendering and simple modification of complex objects (e.g., trees). For display, hardware-accelerated 3-D point rendering is used, but our sampling method can be used by any other point-rendering approach.
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.
Measuring the Perception of Visual Realism in Images
(The Eurographics Association, 2001) Rademacher, Paul; Lengyel, Jed; Cutrell, Edward; Whitted, Turner; S. J. Gortle and K. Myszkowski
One of the main goals in realistic rendering is to generate images that are indistinguishable from photographs but how do observers decide whether an image is photographic or computer-generated? If this perceptual process were understood, then rendering algorithms could be developed to directly target these cues. In this paper we introduce an experimental method for measuring the perception of visual realism in images, and present the results of a series of controlled human subject experiments. These experiments cover the following visual factors: shadow softness, surface smoothness, number of light sources, number of objects, and variety of object shapes. This technique can be used to either affirm or cast into doubt common assumptions about realistic rendering. The experiments can be performed using either photographs or computergenerated images. This work provides a first step towards objectively understanding why some images are perceived as photographs, while others as computer graphics.
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.
Path differentials and applications
(The Eurographics Association, 2001) Suykens, Frank; Willems, Yves D.; S. J. Gortle and K. Myszkowski
Photo-realistic rendering algorithms such as Monte Carlo ray tracing sample individual paths to compute images. Noise and aliasing artefacts are usually reduced by supersampling. Knowledge about the neighborhood of the path, such as an estimated footprint, can be used to reduce these artefacts without having to trace additional paths. The recently introduced ray differentials estimate such a footprint for classical ray tracing, by computing ray derivatives with respect to the image plane. The footprint proves to be useful for filtering textures locally on surfaces. In this paper, we generalize the use of these derivatives to arbitrary path sampling, including general reflection and refraction functions. Sampling new directions introduces additional partial derivatives, which are all combined into a footprint estimate. Additionally the path gradient is introduced; it gives the rate of change of the path contribution. When this change is too steep the size of the footprint is reduced. The resulting footprint can be used in any global illumination algorithm that is based on path sampling. Two applications show its potential: texture filtering in distributed ray tracing and a novel hierarchical approach to particle tracing radiosity.
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.
A Perceptually-Based Texture Caching Algorithm for Hardware-Based Rendering
(The Eurographics Association, 2001) Dumont, Reynald; Pellacini, Fabio; Ferwerda, James A.; S. J. Gortle and K. Myszkowski
The performance of hardware-based interactive rendering systems is often constrained by polygon fill rates and texture map capacity, rather than polygon count alone. We present a new software texture caching algorithm that optimizes the use of texture memory in current graphics hardware by dynamically allocating more memory to the textures that have the greatest visual importance in the scene. The algorithm employs a resource allocation scheme that decides which resolution to use for each texture in board memory. The allocation scheme estimates the visual importance of textures using a perceptually-based metric that takes into account view point and vertex illumination as well as texture contrast and frequency content. This approach provides high frame rates while maximizing image quality.
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.
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.
Real-Time High-Dynamic Range Texture Mapping
(The Eurographics Association, 2001) Cohen, Jonathan; Tchou, Chris; Hawkins, Tim; Debevec, Paul; S. J. Gortle and K. Myszkowski
This paper presents a technique for representing and displaying high dynamic-range texture maps (HDRTMs) using current graphics hardware. Dynamic range in real-world environments often far exceeds the range representable in 8-bit per-channel texture maps. The increased realism afforded by a highdynamic range representation provides improved fidelity and expressiveness for interactive visualization of image-based models. Our technique allows for realtime rendering of scenes with arbitrary dynamic range, limited only by available texture memory. In our technique, high-dynamic range textures are decomposed into sets of 8- bit textures. These 8-bit textures are dynamically reassembled by the graphics hardware s programmable multitexturing system or using multipass techniques and framebuffer image processing. These operations allow the exposure level of the texture to be adjusted continuously and arbitrarily at the time of rendering, correctly accounting for the gamma curve and dynamic range restrictions of the display device. Further, for any given exposure only two 8-bit textures must be resident in texture memory simultaneously. We present implementation details of this technique on various 3D graphics hardware architectures. We demonstrate several applications, including high-dynamic range panoramic viewing with simulated auto-exposure, real-time radiance environment mapping, and simulated Fresnel reflection.

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