EGSR05: 16th Eurographics Symposium on Rendering

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https://diglib.eg.org/handle/10.2312/384

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Texture Tiling on Arbitrary Topological Surfaces using Wang Tiles
(The Eurographics Association, 2005) Fu, Chi-Wing; Leung, Man-Kang; Kavita Bala and Philip Dutre
Synthesizing textures on arbitrary surfaces is a time consuming process. We have to analyze the surface geometry and map texture values onto the input surface adaptively. Texture tiling provides an alternative approach by decoupling the texture synthesis process into two steps: surface mapping and tile placement. This paper reformulates the texture tiling mechanism of Wang tiles for arbitrary topological surfaces. Once we created a low distortion conformal map from the input surface to a quad-based geometry, we can generate a tiling graph over the geometric dual graph of the quad-based geometry, and produce a proper tile orientation on all quad faces so that we can layout textured tiles on quads and map texture back to the input surface accordingly. Since tile placement is independent of the input surface geometry, we can perform the tiling process in no time and change texture pattern on the input surface simply by switching a tile set. No additional computation is needed. As a demonstration, we experimented texture tiling of Wang tiles on spheres, polycubes, as well as polycube-mapped models.
A Dual Light Stage
(The Eurographics Association, 2005) Hawkins, Tim; Einarsson, Per; Debevec, Paul; Kavita Bala and Philip Dutre
We present a technique for capturing high-resolution 4D reflectance fields using the reciprocity property of light transport. In our technique we place the object inside a diffuse spherical shell and scan a laser across its surface. For each incident ray, the object scatters a pattern of light onto the inner surface of the sphere, and we photograph the resulting radiance from the sphere s interior using a camera with a fisheye lens. Because of reciprocity, the image of the inside of the sphere corresponds to the reflectance function of the surface point illuminated by the laser, that is, the color that point would appear to a camera along the laser ray when the object is lit from each direction on the surface of the sphere. The measured reflectance functions allow the object to be photorealistically rendered from the laser s viewpoint under arbitrary directional illumination conditions. Since each captured re- flectance function is a high-resolution image, our data reproduces sharp specular reflections and self-shadowing more accurately than previous approaches. We demonstrate our technique by scanning objects with a wide range of reflectance properties and show accurate renderings of the objects under novel illumination conditions.
Bayesian Relighting
(The Eurographics Association, 2005) Fuchs, Martin; Blanz, Volker; Seidel, Hans-Peter; Kavita Bala and Philip Dutre
We present a simple method for relighting real objects viewed from a fixed camera position. Instead of setting up a calibrated measurement device, such as a light stage, we manually sweep a spotlight over the walls of a white room, illuminating the object indirectly. In contrast to previous methods, we use arbitrary and unknown angular distributions of incoming light. Neither the incident light nor the reflectance function need to be represented explicitly in our approach. The new method relies on images of a probe object, for instance a black snooker ball, placed near the target object. Pictures of the probe in a novel illumination are decomposed into a linear combination of measured images of the probe. Then, a linear combination of images of the target object with the same coefficients produces a synthetic image with the new illumination. We use a simple Bayesian approach to find the most plausible output image, given the picture of the probe and the statistics observed in the dataset of samples. Our results for a variety of novel illuminations, including synthetic lighting by relatively narrow light sources as well as natural illuminations, demonstrate that the new technique is a useful, low cost alternative to existing techniques for a broad range of objects and materials.
Importance Resampling for Global Illumination
(The Eurographics Association, 2005) Talbot, Justin; Cline, David; Egbert, Parris; Kavita Bala and Philip Dutre
This paper develops importance resampling into a variance reduction technique for Monte Carlo integration. Importance resampling is a sample generation technique that can be used to generate more equally weighted samples for importance sampling. This can lead to significant variance reduction over standard importance sampling for common rendering problems. We show how to select the importance resampling parameters for near optimal variance reduction. We demonstrate the robustness of this technique on common global illumination problems and achieve a 10%-70% variance reduction over standard importance sampling for direct lighting. We conclude that further variance reduction could be achieved with cheaper sampling methods.
Ray Maps for Global Illumination
(The Eurographics Association, 2005) Havran, Vlastimil; Bittner, Jiri; Herzog, Robert; Seidel, Hans-Peter; Kavita Bala and Philip Dutre
We describe a novel data structure for representing light transport called ray map. The ray map extends the concept of photon maps: it stores not only photon impacts but the whole photon paths. We demonstrate the utility of ray maps for global illumination by eliminating boundary bias and reducing topological bias of density estimation in global illumination. Thanks to the elimination of boundary bias we could use ray maps for fast direct visualization with the image quality being close to that obtained by the expensive final gathering step. We describe in detail our implementation of the ray map using a lazily constructed kD-tree. We also present several optimizations bringing the ray map query performance close to the performance of the photon map.
Table-top Computed Lighting for Practical Digital Photography
(The Eurographics Association, 2005) Mohan, Ankit; Tumblin, Jack; Bodenheimer, Bobby; Grimm, Cindy; Bailey, Reynold; Kavita Bala and Philip Dutre
We apply simplified image-based lighting methods to reduce the equipment, cost, time, and specialized skills required for high-quality photographic lighting of desktop-sized static objects such as museum artifacts. We place the object and a computer-steered moving-head spotlight inside a simple foam-core enclosure, and use a camera to quickly record low-resolution photos as the light scans the box interior. Optimization guided by interactive user sketching selects a small set of frames whose weighted sum best matches the target image. The system then repeats the lighting used in each of these frames, and constructs a high resolution result from re-photographed basis images. Unlike previous image-based relighting efforts, our method requires only one light source, yet can achieve high resolution light positioning to avoid multiple sharp shadows. A reduced version uses only a hand-held light, and may be suitable for battery-powered, field photography equipment that fits in a backpack.
Colorization by Example
(The Eurographics Association, 2005) Irony, Revital; Cohen-Or, Daniel; Lischinski, Dani; Kavita Bala and Philip Dutre
We present a new method for colorizing grayscale images by transferring color from a segmented example image. Rather than relying on a series of independent pixel-level decisions, we develop a new strategy that attempts to account for the higher-level context of each pixel. The colorizations generated by our approach exhibit a much higher degree of spatial consistency, compared to previous automatic color transfer methods [WAM02]. We also demonstrate that our method requires considerably less manual effort than previous user-assisted colorization methods [LLW04]. Given a grayscale image to colorize, we first determine for each pixel which example segment it should learn its color from. This is done automatically using a robust supervised classification scheme that analyzes the low-level feature space defined by small neighborhoods of pixels in the example image. Next, each pixel is assigned a color from the appropriate region using a neighborhood matching metric, combined with spatial filtering for improved spatial coherence. Each color assignment is associated with a confidence value, and pixels with a sufficiently high confidence level are provided as micro-scribbles to the optimization-based colorization algorithm of Levin et al. [LLW04], which produces the final complete colorization of the image.
Fast Exact From-Region Visibility in Urban Scenes
(The Eurographics Association, 2005) Bittner, Jiri; Wonka, Peter; Wimmer, Michael; Kavita Bala and Philip Dutre
We present a fast exact from-region visibility algorithm for 2.5D urban scenes. The algorithm uses a subdivision of line space for identifying visibility interactions in a 2D footprint of the scene. Visibility in the remaining vertical dimension is resolved by testing for the existence of lines stabbing sequences of virtual portals. Our results show that exact analytic from-region visibility in urban scenes can be computed at times comparable or even superior to recent conservative methods.
Real-Time Multiple Scattering in Participating Media with Illumination Networks
(The Eurographics Association, 2005) Szirmay-Kalos, László; Sbert, Mateu; Ummenhoffer, Tamás; Kavita Bala and Philip Dutre
This paper proposes a real-time method to compute multiple scattering in non-homogeneous participating media having general phase functions. The volume represented by a particle system is supposed to be static, but the lights and the camera may move. Lights can be arbitrarily close to the volume and can even be inside. Real-time performance is achieved by reusing light scattering paths that are generated with global line bundles traced in sample directions in a preprocessing phase. For each particle we obtain those other particles which can be seen in one of the sample directions, and their radiances toward the given particle. This information is stored in an illumination network that allows the fast iteration of the volumetric rendering equation. The illumination network can be stored in two-dimensional arrays indexed by the particles and the directions, respectively. Interpreting these two-dimensional arrays as texture maps, the iteration of the scattering steps can be efficiently executed by the graphics hardware, and the illumination can spread over the media in real-time.
Stippling and Silhouettes Rendering in Geometry-Image Space
(The Eurographics Association, 2005) Yuan, Xiaoru; Nguyen, Minh X.; Zhang, Nan; Chen, Baoquan; Kavita Bala and Philip Dutre
We present a novel non-photorealistic rendering method that performs all operations in a geometry-image domain. We first apply global conformal parameterization to the input geometry model and generate corresponding geometry images. Strokes and silhouettes are then computed in the geometry-image domain. The geometry-image space provides combined benefits of the existing image space and object space approaches. It allows us to take advantage of the regularity of 2D images and yet still have full access to the object geometry information. A wide range of image processing tools can be leveraged to assist various operations involved in achieving non-photorealistic rendering with coherence.
Perceptually Based Tone Mapping of High Dynamic Range Image Streams
(The Eurographics Association, 2005) Irawan, Piti; Ferwerda, James A.; Marschner, Stephen R.; Kavita Bala and Philip Dutre
This paper presents a new perceptually based tone mapping operator that represents scene visibility under timevarying, high dynamic range conditions. The operator is based on a new generalized threshold model that extends the conventional threshold-versus-intensity (TVI) function to account for the viewer s adaptation state, and a new temporal adaptation model that includes fast and slow neural mechanisms as well as photopigment bleaching. These new visual models allow the operator to produce tone-mapped image streams that represent the loss of visibility experienced under changing illumination conditions and in high dynamic range scenes. By varying the psychophysical data that the models use, we simulate the differences in scene visibility experienced by normal and visually impaired observers.
Adaptive Numerical Cumulative Distribution Functions for Efficient Importance Sampling
(The Eurographics Association, 2005) Lawrence, Jason; Rusinkiewicz, Szymon; Ramamoorthi, Ravi; Kavita Bala and Philip Dutre
As image-based surface reflectance and illumination gain wider use in physically-based rendering systems, it is becoming more critical to provide representations that allow sampling light paths according to the distribution of energy in these high-dimensional measured functions. In this paper, we apply algorithms traditionally used for curve approximation to reduce the size of a multidimensional tabulated Cumulative Distribution Function (CDF) by one to three orders of magnitude without compromising its fidelity. These adaptive representations enable new algorithms for sampling environment maps according to the local orientation of the surface and for multiple importance sampling of image-based lighting and measured BRDFs.
Reflectance Sharing: Image-based Rendering from a Sparse Set of Images
(The Eurographics Association, 2005) Zickler, Todd; Enrique, Sebastian; Ramamoorthi, Ravi; Belhumeur, Peter; Kavita Bala and Philip Dutre
When the shape of an object is known, its appearance is determined by the spatially-varying reflectance function defined on its surface. Image-based rendering methods that use geometry seek to estimate this function from image data. Most existing methods recover a unique angular reflectance function (e.g., BRDF) at each surface point and provide reflectance estimates with high spatial resolution. Their angular accuracy is limited by the number of available images, and as a result, most of these methods focus on capturing parametric or low-frequency angular reflectance effects, or allowing only one of lighting or viewpoint variation. We present an alternative approach that enables an increase in the angular accuracy of a spatially-varying reflectance function in exchange for a decrease in spatial resolution. By framing the problem as scattered-data interpolation in a mixed spatial and angular domain, reflectance information is shared across the surface, exploiting the high spatial resolution that images provide to fill the holes between sparsely observed view and lighting directions. Since the BRDF typically varies slowly from point to point over much of an object's surface, this method enables image-based rendering from a sparse set of images without assuming a parametric reflectance model. In fact, the method can even be applied in the limiting case of a single input image.
Metropolis Photon Sampling with Optional User Guidance
(The Eurographics Association, 2005) Fan, Shaohua; Chenney, Stephen; Lai, Yu-chi; Kavita Bala and Philip Dutre
We present Metropolis Photon Sampling (MPS), a visual importance-driven algorithm for populating photon maps. Photon Mapping and other particle tracing algorithms fail if the photons are poorly distributed. Our approach samples light transport paths that join a light to the eye, which accounts for the viewer in the sampling process and provides information to improve photon storage. Paths are sampled with a Metropolis-Hastings algorithm that exploits coherence among important light paths. We also present a technique for including user selected paths in the sampling process without introducing bias. This allows a user to provide hints about important paths or reduce variance in specific parts of the image. We demonstrate MPS with a range of scenes and show quantitative improvements in error over standard Photon Mapping and Metropolis Light Transport.
Out of Core Photon-Mapping for Large Buildings
(The Eurographics Association, 2005) Fradin, David; Meneveaux, Daniel; Horna, Sebastien; Kavita Bala and Philip Dutre
This paper describes a new scheme for computing out-of-core global illumination in complex indoor scenes using a photon-mapping approach. Our method makes use of a cells-and-portals representation of the environment for preserving memory coherence and storing rays or photons. We have successfully applied our method to various buildings, composed of up to one billion triangles. As shown in the results, our method requires only a few hundred megabytes of memory for tracing more than 1.6 billion photons in large buildings.
Online Construction of Surface Light Fields
(The Eurographics Association, 2005) Coombe, Greg; Hantak, Chad; Lastra, Anselmo; Grzeszczuk, Radek; Kavita Bala and Philip Dutre
We present a system for interactively capturing, constructing, and rendering surface light fields by incrementally building a low rank approximation to the surface light field. Each image is incorporated into the lighting model as it is captured, providing the user with real-time feedback. This feedback enables the user to preview the lighting model and direct the image acquisition towards undersampled areas of the object. We also provide a novel datadriven quality heuristic to aid the user in identifying undersampled regions. Our system is an order of magnitude faster than previous systems, and reduces the time necessary to capture the images and construct a surface light field from hours to minutes.
Estimation of 3D Faces and Illumination from Single Photographs Using A Bilinear Illumination Model
(The Eurographics Association, 2005) Lee, Jinho; Pfister, Hanspeter; Moghaddam, Baback; Machiraju, Raghu; Kavita Bala and Philip Dutre
3D Face modeling is still one of the biggest challenges in computer graphics. In this paper we present a novel framework that acquires the 3D shape, texture, pose and illumination of a face from a single photograph. Additionally, we show how we can recreate a face under varying illumination conditions. Or, essentially relight it. Using a custom-built face scanning system, we have collected 3D face scans and light reflection images of a large and diverse group of human subjects. We derive a morphable face model for 3D face shapes and accompanying textures by transforming the data into a linear vector sub-space. The acquired images of faces under variable illumination are then used to derive a bilinear illumination model that spans 3D face shape and illumination variations. Using both models we, in turn, propose a novel fitting framework that estimates the parameters of the morphable model given a single photograph. Our framework can deal with complex face reflectance and lighting environments in an efficient and robust manner. In the results section of our paper, we compare our methods to existing ones and demonstrate its efficacy in reconstructing 3D face models when provided with a single photograph. We also provide several examples of facial relighting (on 2D images) by performing adequate decomposition of the estimated illumination using our framework.
Real Illumination from Virtual Environments
(The Eurographics Association, 2005) Ghosh, Abhijeet; Trentacoste, Matthew; Seetzen, Helge; Heidrich, Wolfgang; Kavita Bala and Philip Dutre
We introduce a method for actively controlling the illumination in a room so that it is consistent with a virtual world. In combination with a high dynamic range display, the system produces both uniform and directional illumination at intensity levels covering a wide range of real-world environments. It thereby allows natural adaptation processes of the human visual system to take place, for example when moving between bright and dark environments. In addition, the directional illumination provides additional information about the environment in the user s peripheral field of view. We describe both the hardware and the software aspects of our system. We also conducted an informal survey to determine whether users prefer the dynamic illumination over constant room illumination in an entertainment setting.
Non-linear Volume Photon Mapping
(The Eurographics Association, 2005) Gutierrez, Diego; Munoz, Adolfo; Anson, Oscar; Seron, Francisco J.; Kavita Bala and Philip Dutre
This paper describes a novel extension of the photon mapping algorithm, capable of handling both volume multiple inelastic scattering and curved light paths simultaneously. The extension is based on the Full Radiative Transfer Equation (FRTE) and Fermat's law, and yields physically accurate, high-dynamic data than can be used for image generation or for other simulation purposes, such as driving simulators, underwater vision or lighting studies in architecture. Photons are traced into the participating medium with a varying index of refraction, and their curved trajectories followed (curved paths are the cause of certain atmospheric effects such as mirages or rippling desert images). Every time a photon is absorbed, a Russian roulette algorithm based on the quantum efficiency of the medium determines whether the inelastic scattering event takes place (causing volume fluorescence). The simulation of both underwater and atmospheric effects is shown, providing a global illumination solution without the restrictions of previous approaches.
Bidirectional Importance Sampling for Direct Illumination
(The Eurographics Association, 2005) Burke, David; Ghosh, Abhijeet; Heidrich, Wolfgang; Kavita Bala and Philip Dutre
Image-based representations for illumination can capture complex real-world lighting that is difficult to represent in other forms. Current importance sampling strategies for image-based illumination have difficulties in cases where both the illumination and the surface BRDF contain important high-frequency detail for example, when a specular surface is illuminated by an environment map containing small light sources. We introduce the notion of bidirectional importance sampling, in which samples are drawn from the product distribution of both the surface reflectance and the light source energy. While this approach makes the sample selection process more expensive, we drastically reduce the number of visibility tests required to obtain good image quality. As a consequence, we achieve significant quality improvements over previous sampling strategies for the same compute time. Keywords: Methods and Applications Monte Carlo Techniques; Rendering Ray Tracing; Rendering Global Illumination.

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