EGSR04: 15th Eurographics Symposium on Rendering

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https://diglib.eg.org/handle/10.2312/383

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Alias-Free Shadow Maps
(The Eurographics Association, 2004) Aila, Timo; Laine, Samuli; Alexander Keller and Henrik Wann Jensen
In this paper we abandon the regular structure of shadow maps. Instead, we transform the visible pixels P(x, y, z) from screen space to the image plane of a light source P0(x0, y0, z0). The (x0, y0) are then used as sampling points when the geometry is rasterized into the shadow map. This eliminates the resolution issues that have plagued shadow maps for decades, e.g., jagged shadow boundaries. Incorrect self-shadowing is also greatly reduced, and semi-transparent shadow casters and receivers can be supported. A hierarchical software implementation is outlined
All-focused light field rendering
(The Eurographics Association, 2004) Kubota, Akira; Takahashi, Keita; Aizawa, Kiyoharu; Chen, Tsuhan; Alexander Keller and Henrik Wann Jensen
We present a novel reconstruction method that can synthesize an all in-focus view from under-sampled light fields, significantly suppressing aliasing artifacts. The presented method consists of two steps; 1) rendering multiple views at a given view point by performing light field rendering with different focal plane depths; 2) iteratively reconstructing the all in-focus view by fusing the multiple views. We model the multiple views and the desired all in-focus view as a set of linear equations with a combination of textures at the focal depths. Aliasing artifacts can be modeled as spatially (shift) varying filters. We can solve this set of linear equations by using an iterative reconstruction approach. This method effectively integrates focused regions in each view into an all in-focus view without any local processing steps such as estimation of depth or segmentation of the focused regions.
All-Frequency Precomputed Radiance Transfer for Glossy Objects
(The Eurographics Association, 2004) Liu, Xinguo; Sloan, Peter-Pike; Shum, Heung-Yeung; Snyder, John; Alexander Keller and Henrik Wann Jensen
We introduce a method based on precomputed radiance transfer (PRT) that allows interactive rendering of glossy surfaces and includes shadowing effects from dynamic, "all-frequency" lighting. Specifically, source lighting is represented by a cube map at resolution nL
All-Frequency Relighting of Non-Diffuse Objects using Separable BRDF Approximation
(The Eurographics Association, 2004) Wang, Rui; Tran, John; Luebke, David; Alexander Keller and Henrik Wann Jensen
This paper presents a technique, based on pre-computed light transport and separable BRDF approximation, for interactive rendering of non-diffuse objects under all-frequency environment illumination. Existing techniques using spherical harmonics to represent environment maps and transport functions are limited to low-frequency light transport effects. Non-linear wavelet lighting approximation is able to capture all-frequency illumination and shadows for geometry relighting, but interactive rendering is currently limited to diffuse objects. Our work extends the wavelet-based approach to relighting of non-diffuse objects. We factorize the BRDF using separable decomposition and keep only a few low-order approximation terms, each consisting of a 2D light map paired with a 2D view map. We then pre-compute light transport matrices corresponding to each BRDF light map, and compress the data with a non-linear wavelet approximation. We use modern graphics hardware to accelerate precomputation. At run-time, a sparse light vector is multiplied by the sparse transport matrix at each vertex, and the results are further combined with texture lookups of the view direction into the BRDF view maps to produce view-dependent color. Using our technique, we demonstrate rendering of objects with several non-diffuse BRDFs under all-frequency, dynamic environment lighting at interactive rates.
An Analytical Model for Skylight Polarisation
(The Eurographics Association, 2004) Wilkie, A.; Ulbricht, C.; Tobler, Robert F.; Zotti, G.; Purgathofer, W.; Alexander Keller and Henrik Wann Jensen
Under certain circumstances the polarisation state of the illumination can have a significant influence on the appearance of scenes; outdoor scenes with specular surfaces - such as water bodies or windows - under clear, blue skies are good examples of such environments. In cases like that it can be essential to use a polarising renderer if a true prediction of nature is intended, but so far no polarising skylight models have been presented. This paper presents a plausible analytical model for the polarisation of the light emitted from a clear sky. Our approach is based on a suitable combination of several components with well-known characteristics, and yields acceptable results in considerably less time than an exhaustive simulation of the underlying atmospheric scattering phenomena would require.
Animatable Facial Reflectance Fields
(The Eurographics Association, 2004) Hawkins, Tim; Wenger, Andreas; Tchou, Chris; Gardner, Andrew; Göransson, Fredrik; Debevec, Paul; Alexander Keller and Henrik Wann Jensen
We present a technique for creating an animatable image-based appearance model of a human face, able to capture appearance variation over changing facial expression, head pose, view direction, and lighting condition. Our capture process makes use of a specialized lighting apparatus designed to rapidly illuminate the subject sequentially from many different directions in just a few seconds. For each pose, the subject remains still while six video cameras capture their appearance under each of the directions of lighting. We repeat this process for approximately 60 different poses, capturing different expressions, visemes, head poses, and eye positions. The images for each of the poses and camera views are registered to each other semi-automatically with the help of fiducial markers. The result is a model which can be rendered realistically under any linear blend of the captured poses and under any desired lighting condition by warping, scaling, and blending data from the original images. Finally, we show how to drive the model with performance capture data, where the pose is not necessarily a linear combination of the original captured poses.
Anti-aliasing and Continuity with Trapezoidal Shadow Maps
(The Eurographics Association, 2004) Martin, Tobias; Tan, Tiow-Seng; Alexander Keller and Henrik Wann Jensen
This paper proposes a new shadow map technique termed trapezoidal shadow maps to calculate high quality shadows in real-time applications. To address the resolution problem of the standard shadow map approach, our technique approximates the eye's frustum as seen from the light with a trapezoid to warp it onto a shadow map. Such a trapezoidal approximation, which may first seem straightforward, is carefully designed to achieve the goal of good shadow quality for objects from near to far, and to address the continuity problem that is found in all existing shadow map approaches. The continuity problem occurs mainly when the shadow map quality changes significantly from frame to frame due to the motion of the eye or the light. This results in flickering of shadows. On the whole, our proposed approach is simple to implement without using complex data structures and it maps well to graphics hardware as shown in our experiments with large virtual scenes of hundreds of thousands to over a million of triangles.
Bixels: Picture Samples with Sharp Embedded Boundaries
(The Eurographics Association, 2004) Tumblin, Jack; Choudhury, Prasun; Alexander Keller and Henrik Wann Jensen
Pixels store a digital image as a grid of point samples that can reconstruct a limited-bandwidth continuous 2-D source image. Although convenient for anti-aliased display, these bandwidth limits irreversibly discard important visual boundary information that is difficult or impossible to accurately recover from pixels alone. We propose bixels instead: they also store a digital image as a grid of point samples, but each sample keeps 8 extra bits to set embedded geometric boundaries that are infinitely sharp, more accurately placed, and directly machine-readable. Bixels represent images as piecewise-continuous, with discontinuous intensities and gradients at boundaries that form planar graphs. They reversibly combine vector and raster image features, decouple boundary sharpness from the number of samples used to store them, and do not mix unrelated but adjacent image contents, e.g blue sky and green leaf. Bixels are meant to be compatible with pixels. A bixel is a image sample point with an 8 bit code for local boundaries. We describe a boundary-switched bilinear filter kernel for bixel reconstruction and pre-filtering to find bixel samples, a bixels-to-pixels conversion method for display, and an iterative method to combine pixels and given boundaries to make bixels. We discuss applications in texture synthesis, matting and compositing. We demonstrate sharpness-preserving enlargement, warping and bixels-to-pixels conversion with example images.
CC Shadow Volumes
(The Eurographics Association, 2004) Lloyd, D. Brandon; Wendt, Jeremy; Govindaraju, Naga K.; Manocha, Dinesh; Alexander Keller and Henrik Wann Jensen
We present a technique that uses culling and clamping (CC) for accelerating the performance of stencil-based shadow volume computation. Our algorithm reduces the fill requirements and rasterization cost of shadow volumes by reducing unnecessary rendering. A culling step removes shadow volumes that are themselves in shadow or do not contribute to thefinal image. Our novel clamping algorithms restrict shadow volumes to those regions actually containing shadow receivers. In this way, we avoid rasterizing shadow volumes over large regions of empty space. We utilize temporal coherence between successive frames to speed up clamping computations. Even with fairly coarse clamping we obtain substantial reduction in fill requirements and shadow rendering time in dynamic environments composed of up to a 100K triangles.
Combining Higher-Order Wavelets and Discontinuity Meshing: a Compact Representation for Radiosity
(The Eurographics Association, 2004) Holzschuch, N.; Alonso, L.; Alexander Keller and Henrik Wann Jensen
The radiosity method is used for global illumination simulation in diffuse scenes, or as an intermediate step in other methods. Radiosity computations using Higher-Order wavelets achieve a compact representation of the illumination on many parts of the scene, but are more expensive near discontinuities, such as shadow boundaries. Other methods use a mesh, based on the set of discontinuities of the illumination function. The complexity of this set of discontinuities has so far proven prohibitive for large scenes, mostly because of the difficulty to robustly manage a geometrically complex set of triangles. In this paper, we present a method for computing radiosity that uses higher-order wavelet functions as a basis, and introduces discontinuities only when they simplify the resulting mesh. The result is displayed directly, without post-processing.
An Efficient Hybrid Shadow Rendering Algorithm
(The Eurographics Association, 2004) Chan, Eric; Durand, Fredo; Alexander Keller and Henrik Wann Jensen
We present a hybrid algorithm for rendering hard shadows accurately and efficiently. Our method combines the strengths of shadow maps and shadow volumes. We first use a shadow map to identify the pixels in the image that lie near shadow discontinuities. Then, we perform the shadow-volume computation only at these pixels to ensure accurate shadow edges. This approach simultaneously avoids the edge aliasing artifacts of standard shadow maps and avoids the high fillrate consumption of standard shadow volumes. The algorithm relies on a hardware mechanism for rapidly rejecting non-silhouette pixels during rasterization. Since current graphics hardware does not directly provide this mechanism, we simulate it using available features related to occlusion culling and show that dedicated hardware support requires minimal changes to existing technology.
Efficient Rendering of Atmospheric Phenomena
(The Eurographics Association, 2004) Riley, Kirk; Ebert, David S.; Kraus, Martin; Tessendorf, Jerry; Hansen, Charles; Alexander Keller and Henrik Wann Jensen
Rendering of atmospheric bodies involves modeling the complex interaction of light throughout the highly scattering medium of water and air particles. Scattering by these particles creates many well-known atmospheric optical phenomena including rainbows, halos, the corona, and the glory. Unfortunately, most radiative transport approximations in computer graphics are ill-suited to render complex angularly dependent effects in the presence of multiple scattering at reasonable frame rates. Therefore, this paper introduces a multiple-model lighting system that efficiently captures these essential atmospheric effects. We have solved the rendering of fine angularly dependent effects in the presence of multiple scattering by designing a lighting approximation based upon multiple scattering phase functions. This model captures gradual blurring of chromatic atmospheric optical phenomena by handling the gradual angular spreading of the sunlight as it experiences multiple scattering events with anisotropic scattering particles. It has been designed to take advantage of modern graphics hardware; thus, it is capable of rendering these effects at near interactive frame rates.
Estimating source spectra and spectral albedos from RGB data for rerendering
(The Eurographics Association, 2004) Koenderink, J. J.; Alexander Keller and Henrik Wann Jensen
I consider the problem of estimating material properties (the spectral albedo) on the basis of -object colors- (at worst only RGB data say). I show how to obtain a priori likely estimates for the white point, the spectral composition of the source, and the spectral albedos of the objects in a scene. I also show how to construct the general solutions. These general solutions are so broad as to render them practically useless. There are good reasons to disregard the larger part of the solution space, because very general considerations suggest that the specific solutions constructed with the methods discussed here are very likely to yield sensible and useful results in practice. From a principled perspective it is desirable to be able to construct the full solution space though. Since the results are in the scene, rather than the image domain, they are suitable for rerendering purposes.
Feature-Based Textures
(The Eurographics Association, 2004) Ramanarayanan, G.; Bala, K.; Walter, B.; Alexander Keller and Henrik Wann Jensen
This paper introduces feature-based textures, a new image representation that combines features and samples for high-quality texture mapping. Features identify boundaries within an image where samples change discontinuously. They can be extracted from vector graphics representations, or explicitly added to raster images to improve sharpness. Texture lookups are then interpolated from samples while respecting these boundaries. We present results from a software implementation of this technique demonstrating quality, efficiency and low memory overhead.
A Framework for Multiperspective Rendering
(The Eurographics Association, 2004) Yu, J.; McMillan, L.; Alexander Keller and Henrik Wann Jensen
We present a framework for the direct rendering of multiperspective images. We treat multiperspective imaging systems as devices for capturing smoothly varying set of rays, and we show that under an appropriate parametrization, multiperspective images can be characterized as continuous manifolds in ray space. We use a recently introduced class of General Linear Cameras (GLC), which describe all 2D linear subspaces of rays, as primitives for constructing multiperspective images. We show GLCs when constrained by an appropriate set of rules, can be laid out to tile the image plane and, hence, generate arbitrary multiperspective renderings. Our framework can easily render a broad class of multiperspective images, such as multiperspective panoramas, neocubist style renderings, and faux-animations from still-life scenes. We also show a method to minimize distortions in multiperspective images by uniformly sampling rays on a sampling plane even when they do not share a common origin.
Generalized Displacement Maps
(The Eurographics Association, 2004) Wang, Xi; Tong, Xin; Lin, Stephen; Hu, Shimin; Guo, Baining; Shum, Heung-Yeung; Alexander Keller and Henrik Wann Jensen
In this paper, we introduce a real-time algorithm to render the rich visual effects of general non-height-field geometric details, known as mesostructure. Our method is based on a five-dimensional generalized displacement map (GDM) that represents the distance of solid mesostructure along any ray cast from any point within a volumetric sample. With this GDM information, we propose a technique that computes mesostructure visibility jointly in object space and texture space which enables both control of texture distortion and efficient computation of texture coordinates and shadowing. GDM can be rendered with either local or global illumination as a per-pixel process in graphics hardware to achieve real-time rendering of general mesostructure.
Hardware Accelerated Visibility Preprocessing using Adaptive Sampling
(The Eurographics Association, 2004) Nirenstein, S.; Blake, E.; Alexander Keller and Henrik Wann Jensen
We present a novel aggressive visibility preprocessing technique for general 3D scenes. Our technique exploits commodity graphics hardware and is faster than most conservative solutions, while simultaneously not overestimating the set of visible polygons. The cost of this benefit is that of potential image error. In order to reduce image error, we have developed an effective error minimization heuristic. We present results showing the application of our technique to highly complex scenes, consisting of many small polygons. We give performance results, an in depth error analysis using various metrics, and an empirical analysis showing a high degree of scalability. We show that our technique can rapidly compute from-region visibility (1hr 19min for a 5 million polygon forest), with minimal error (0.3% of image). On average 91.3% of the scene is culled.
Hemispherical Rasterization for Self-Shadowing of Dynamic Objects
(The Eurographics Association, 2004) Kautz, Jan; Lehtinen, Jaakko; Aila, Timo; Alexander Keller and Henrik Wann Jensen
We present a method for interactive rendering of dynamic models with self-shadows due to time-varying, lowfrequency lighting environments. In contrast to previous techniques, the method is not limited to static or preanimated models. Our main contribution is a hemispherical rasterizer, which rapidly computes visibility by rendering blocker geometry into a 2D occlusion mask with correct occluder fusion. The response of an object to the lighting is found by integrating the visibility function at each of the vertices against the spherical harmonic functions and the BRDF. This yields transfer coefficients that are then multiplied by the lighting coefficients to obtain the final, shadowed exitant radiance. No precomputation is necessary and memory requirements are modest. The method supports both diffuse and glossy BRDFs.
Image-Based Stereoscopic Painterly Rendering
(The Eurographics Association, 2004) Stavrakis, E.; Gelautz, M.; Alexander Keller and Henrik Wann Jensen
We present a new image-based stereoscopic painterly algorithm that we use to automatically generate stereoscopic paintings. Our work is motivated by contemporary painters who have explored the aesthetic implications of painting stereo pairs of canvases. We base our method on two real images, acquired from spatially displaced cameras. We derive a depth map by utilizing computer vision depth-from-stereo techniques and use this information to plan and render stereo paintings. These paintings can be viewed stereoscopically, in which case the pictorial medium is perceptually extended by the viewer to better suggest the sense of distance.
An Interactive Out-of-Core Rendering Framework for Visualizing Massively Complex Models
(The Eurographics Association, 2004) Wald, Ingo; Dietrich, Andreas; Slusallek, Phlipp; Alexander Keller and Henrik Wann Jensen
With the tremendous advances in both hardware capabilities and rendering algorithms, rendering performance is steadily increasing. Even consumer graphics hardware can render many million triangles per second. However, scene complexity seems to be rising even faster than rendering performance, with no end to even more complex models in sight. In this paper, we are targeting the interactive visualization of the "Boeing 777" model, a highly complex model of 350 million individual triangles, which - due to its sheer size and complex internal structure - simply cannot be handled satisfactorily by today's techniques. To render this model, we use a combination of real-time ray tracing, a low-level out of core caching and demand loading strategy, and a hierarchical, hybrid volumetric/lightfield-like approximation scheme for representing not-yet-loaded geometry. With this approach, we are able to render the full 777 model at several frames per second even on a single commodity desktop PC.

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