EGSR04: 15th Eurographics Symposium on Rendering

Permanent URI for this collection

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

Browse

Now showing 1 - 20 of 41

Spherical Harmonic Gradients for Mid-Range Illumination
(The Eurographics Association, 2004) Annen, Thomas; Kautz, Jan; Durand, Frédo; Seidel, Hans-Peter; Alexander Keller and Henrik Wann Jensen
Spherical harmonics are often used for compact description of incident radiance in low-frequency but distant lighting environments. For interaction with nearby emitters, computing the incident radiance at the center of an object only is not sufficient. Previous techniques then require expensive sampling of the incident radiance field at many points distributed over the object. Our technique alleviates this costly requirement using a first-order Taylor expansion of the spherical-harmonic lighting coefficients around a point. We propose an interpolation scheme based on these gradients requiring far fewer samples (one is often sufficient). We show that the gradient of the incident-radiance spherical harmonics can be computed for little additional cost compared to the coefficients alone. We introduce a semi-analytical formula to calculate this gradient at run-time and describe how a simple vertex shader can interpolate the shading. The interpolated representation of the incident radiance can be used with any low-frequency light-transfer technique.
Real-time appearance preserving out-of-core rendering with shadows
(The Eurographics Association, 2004) Guthe, Michael; Borodin, Pavel; Balázs, Ákos; Klein, Reinhard; Alexander Keller and Henrik Wann Jensen
Despite recent advances in finding efficient LOD-representations for gigantic 3D objects, rendering of complex, gigabyte-sized models and environments is still a challenging task, especially under real-time constraints and high demands on the visual accuracy. The two general approaches are using either a polygon- or a point-based representation for the simplified geometry. With the polygon-based approaches high frame rates can be achieved by sacrificing the exact appearance and thus the image quality. Point-based approaches on the other hand preserve higher image quality at the cost of higher primitive counts and therefore lower frame rates. In this paper we present a new hybrid point-polygon LOD algorithm for real-time rendering of complex models and environments including shadows. While rendering different LODs, we preserve the appearance of an object by using a novel error measure for simplification which allows us to steer the LOD generation in such a way that the geometric as well as the appearance deviation is bounded in image space. Additionally, to enhance the perception of the models shadows should be used. We present a novel LOD selection and prefetching method for real-time rendering of hard shadows. In contrast to the only currently available method for out-of-core shadow generation, our approach entirely runs on a single CPU system.
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.
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
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.
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.
A Novel Hemispherical Basis for Accurate and Efficient Rendering
(The Eurographics Association, 2004) Gautron, Pascal; Krivanek, Jaroslav; Pattanaik, Sumanta; Bouatouch, Kadi; Alexander Keller and Henrik Wann Jensen
This paper presents a new set of hemispherical basis functions dedicated to hemispherical data representation. These functions are derived from associated Legendre polynomials. We demonstrate the usefulness of this basis for representation of surface reflectance functions, rendering using environment maps and for efficient global illumination computation using radiance caching. We show that our basis is more appropriate for hemispherical functions than spherical harmonics. This basis can be efficiently combined with spherical harmonics in applications involving both hemispherical and spherical data.
An Irradiance Atlas for Global Illumination in Complex Production Scenes
(The Eurographics Association, 2004) Christensen, Per H.; Batali, Dana; Alexander Keller and Henrik Wann Jensen
We introduce a tiled 3D MIP map representation of global illumination data. The representation is an adaptive, sparse octree with a "brick" at each octree node; each brick consists of 8 <sup>3</sup> voxels with sparse irradiance values. The representation is designed to enable efficient caching. Combined with photon tracing and recent advances in distribution ray tracing of very complex scenes, the result is a method for efficient and flexible computation of global illumination in very complex scenes. The method can handle scenes with many more textures, geometry, and photons than could fit in memory. We show an example of a CG movie scene that has been retrofitted with global illumination shading using our method.
Programmable Style for NPR Line Drawing
(The Eurographics Association, 2004) Grabli, Stéphane; Turquin, Emmanuel; Durand, Frédo; Sillion, François X.; Alexander Keller and Henrik Wann Jensen
This paper introduces a programmable approach to non-photorealistic line drawing from 3D models, inspired by programmable shaders in traditional rendering. We propose a new image creation model where all operations are controlled through user-defined procedures. A view map describing all relevant support lines in the drawing and their topological arrangement is first created from the 3D model; a number of style modules operate on this map, by procedurally selecting, chaining or splitting lines, before creating strokes and assigning drawing attributes. The resulting drawing system permits flexible control of all elements of drawing style: first, different style modules can be applied to different types of lines in a view; second, the topology and geometry of strokes are entirely controlled from the programmable modules; and third, stroke attributes are assigned procedurally and can be correlated at will with various scene or view properties. Finally, we propose new density control strategies where strokes can be adapted or omitted to avoid visual clutter. We illustrate the components of our system and show how style modules successfully capture stylized visual characteristics that can be applied across a wide range of models.
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.
A Lixel for every Pixel
(The Eurographics Association, 2004) Chong, Hamilton Y.; Gortler, Steven J.; Alexander Keller and Henrik Wann Jensen
Shadow mapping is a very useful tool for generating shadows in many real-time rendering settings and is even used in some off-line renderers. One of the difficulties when using a shadow map is obtaining a sufficiently dense sampling on shadowed surfaces to minimize shadow aliasing. Endlessly upping the light-image resolution is not always a viable option. In this paper we describe a shadow mapping technique that guarantees, that over a small number of chosen planes of interest (such as a floor and a wall), the shadow map is, in fact, perfectly sampled, ie. for each pixel in the viewer camera, there will be exactly one lixel in the shadow map that samples the exact same geometric point.
Light Space Perspective Shadow Maps
(The Eurographics Association, 2004) Wimmer, Michael; Scherzer, Daniel; Purgathofer, Werner; Alexander Keller and Henrik Wann Jensen
In this paper, we present a new shadow mapping technique that improves upon the quality of perspective and uniform shadow maps. Our technique uses a perspective transform specified in light space which allows treating all lights as directional lights and does not change the direction of the light sources. This gives all the benefits of the perspective mapping but avoids the problems inherent in perspective shadow mapping like singularities in post-perspective space, missed shadow casters etc. Furthermore, we show that both uniform and perspective shadow maps distribute the perspective aliasing error that occurs in shadow mapping unequally over the available depth range. We therefore propose a transform that equalizes this error and gives equally pleasing results for near and far viewing distances. Our method is simple to implement, requires no scene analysis and is therefore as fast as uniform shadow mapping.
Rendering Evolution at Industrial Light and Magic
(The Eurographics Association, 2004) Hery, Christophe; Alexander Keller and Henrik Wann Jensen
From Jurassic Park to Van Helsing, the rendering technologies at ILM have evolved over the last 10 years, both to satisfy the high demands of our clients and also those of the general public. State-of-the-art rendering techniques such as volume rendering, ambient occlusion, image-based rendering, sub-surface scattering and global illumination are now in common use. This summary will give a brief history of how rendering schemes came to be deployed (and fairly often pioneered) at our facility and the challenges they brought with them.
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.
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.
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.
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.
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.
Progressively-Refined Reflectance Functions from Natural Illumination
(The Eurographics Association, 2004) Matusik, Wojciech; Loper, Matthew; Pfister, Hanspeter; Alexander Keller and Henrik Wann Jensen
In this paper we present a simple, robust, and efficient algorithm for estimating reflectance fields (i.e., a description of the transport of light through a scene) for a fixed viewpoint using images of the scene under known natural illumination. Our algorithm treats the scene as a black-box linear system that transforms an input signal (the incident light) into an output signal (the reflected light). The algorithm is hierarchical - it progressively refines the approximation of the reflectance field with an increasing number of training samples until the required precision is reached. Our method relies on a new representation for reflectance fields. This representation is compact, can be progressively refined, and quickly computes the relighting of scenes with complex illumination. Our representation and the corresponding algorithm allow us to efficiently estimate the reflectance fields of scenes with specular, glossy, refractive, and diffuse elements. The method also handles soft and hard shadows, inter-reflections, caustics, and subsurface scattering. We verify our algorithm and representation using two measurement setups and several scenes, including an outdoor view of the city of Cambridge.
Practical Rendering of Multiple Scattering Effects in Participating Media
(The Eurographics Association, 2004) Premoze, Simon; Ashikhmin, Michael; Tessendorf, Jerry; Ramamoorthi, Ravi; Nayar, Shree; Alexander Keller and Henrik Wann Jensen
Volumetric light transport effects are significant for many materials like skin, smoke, clouds, snow or water. In particular, one must consider the multiple scattering of light within the volume. While it is possible to simulate such media using volumetric Monte Carlo or finite element techniques, those methods are very computationally expensive. On the other hand, simple analytic models have so far been limited to homogeneous and/or optically dense media and cannot be easily extended to include strongly directional effects and visibility in spatially varying volumes. We present a practical method for rendering volumetric effects that include multiple scattering. We show an expression for the point spread function that captures blurring of radiance due to multiple scattering. We develop a general framework for incorporating this point spread function, while considering inhomogeneous media - this framework could also be used with other analytic multiple scattering models.

Browse

Browsing EGSR04: 15th Eurographics Symposium on Rendering by Issue Date

Results Per Page

Sort Options