EGSR05: 16th Eurographics Symposium on Rendering

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

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Multiresolution Reflectance Filtering
(The Eurographics Association, 2005) Tan, Ping; Lin, Stephen; Quan, Long; Guo, Baining; Shum, Heung-Yeung; Kavita Bala and Philip Dutre
Physically-based reflectance models typically represent light scattering as a function of surface geometry at the pixel level. With changes in viewing resolution, the geometry imaged within a pixel can undergo significant variations that result in changing reflectance characteristics. To address these transformations, we present a multiresolution reflectance framework based on microfacet normal distributions within a pixel over different scales. Since these distributions must be efficiently determined with respect to resolution, they are recorded at multiple resolution levels in mipmaps. The main contribution of this work is a real-time mipmap filtering technique for these distribution-based parameters that not only provides smooth reflectance transitions in scale, but also minimizes aliasing. With this multiresolution reflectance technique, our system can rapidly and accurately incorporate fine reflectance detail that is customarily disregarded in multiresolution rendering methods.
A Hybrid Monte Carlo Method for Accurate and Efficient Subsurface Scattering
(The Eurographics Association, 2005) Li, Hongsong; Pellacini, Fabio; Torrance, Kenneth E.; Kavita Bala and Philip Dutre
Subsurface scattering is a fundamental aspect of surface appearance responsible for the characteristic look of many materials. Monte Carlo path tracing techniques can be employed with high accuracy to simulate the scattering of light inside a translucent object, albeit at the cost of long computation times. In a seminal work, Jensen et al. [JMLH01] presented a more efficient technique to simulate subsurface scattering that, while producing accurate results for translucent, optically-thick, materials, exhibits artifacts for semi-transparent, optically-thin, ones, especially in regions of high-curvature. This paper presents a hybrid Monte Carlo technique capable of simulating a wide range of materials exhibiting subsurface scattering, from translucent to semi-transparent ones, with an accuracy comparable to Monte Carlo techniques but at a much lower computational cost. Our approach utilizes a Monte Carlo path tracing approach for the first several scattering events, in order to estimate the directional-diffuse component of subsurface scattering, and switches to a dipole diffusion approximation only when the path penetrates deeply enough into the surface. By combining the accuracy of Monte Carlo integration with the efficiency of the dipole diffusion approximation, our hybrid method produces results as accurate as full Monte Carlo simulations at a speed comparable to the Jensen et al. approximation, thus extending its usefulness to a much wider range of materials.
Adaptive Frameless Rendering
(The Eurographics Association, 2005) Dayal, Abhinav; Woolley, Cliff; Watson, Benjamin; Luebke, David; Kavita Bala and Philip Dutre
We propose an adaptive form of frameless rendering with the potential to dramatically increase rendering speed over conventional interactive rendering approaches. Without the rigid sampling patterns of framed renderers, sampling and reconstruction can adapt with very fine granularity to spatio-temporal color change. A sampler uses closed-loop feedback to guide sampling toward edges or motion in the image. Temporally deep buffers store all the samples created over a short time interval for use in reconstruction and as sampler feedback. GPU-based reconstruction responds both to sampling density and space-time color gradients. Where the displayed scene is static, spatial color change dominates and older samples are given significant weight in reconstruction, resulting in sharper and eventually antialiased images. Where the scene is dynamic, more recent samples are emphasized, resulting in less sharp but more up-to-date images. We also use sample reprojection to improve reconstruction and guide sampling toward occlusion edges, undersampled regions, and specular highlights. In simulation our frameless renderer requires an order of magnitude fewer samples than traditional rendering of similar visual quality (as measured by RMS error), while introducing overhead amounting to 15% of computation time.
Geometric Clustering for Line Drawing Simplification
(The Eurographics Association, 2005) Barla, Pascal; Thollot, Joelle; Sillion, François X.; Kavita Bala and Philip Dutre
We present a new approach to the simplification of line drawings, in which a smaller set of lines is created to represent the geometry of the original lines. An important feature of our method is that it maintains the morphological structure of the original drawing while allowing user-defined decisions about the appearance of lines. The technique works by analyzing the structure of the drawing at a certain scale and identifying clusters of lines that can be merged given a specific error threshold. These clusters are then processed to create new lines, in a separate stage where different behaviors can be favored based on the application. Successful results are presented for a variety of drawings including scanned and vectorized artwork, original vector drawings, drawings created from 3d models, and hatching marks. The clustering technique is shown to be effective in all these situations.
Inferring Reflectance Functions from Wavelet Noise
(The Eurographics Association, 2005) Peers, Pieter; Dutré, Philip; Kavita Bala and Philip Dutre
This paper presents a novel method for acquiring a wavelet representation of the reflectance field of real objects. Key to our method is the use of wavelet noise illumination to infer a reflectance function for each pixel. Due to their stochastic nature, these wavelet noise patterns enable to trade off the number of recorded photographs for the quality of the computed reflectance functions. Additionally, each wavelet noise pattern affects all pixels in a recorded photograph, independently of the underlying material properties in the scene. Consequently, each recorded photograph contributes additional information to the reflectance field computation. The presented method consists of three steps. First, a fixed number of photographs are recorded of the scene lit by a series of wavelet noise patterns emitted from a CRT monitor. Next, for each pixel a reflectance function is computed offline, by identifying the important wavelet coefficients for the pixel's reflectance function. The coefficients are computed by solving a linear least squares problem. Finally, once all reflectance functions are computed, a novel image of the scene can be composited with arbitrary incident illumination. The method can be used for both image-based relighting and environment matting.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Spherical Q2-tree for Sampling Dynamic Environment Sequences
(The Eurographics Association, 2005) Wan, Liang; Wong, Tien-Tsin; Leung, Chi-Sing; Kavita Bala and Philip Dutre
Previous methods in environment map sampling seldom consider a sequence of dynamic environment maps. The generated sampling patterns of the sequence may not maintain the temporal illumination consistency and result in choppy animation. In this paper, we propose a novel approach, spherical Q2-tree, to address this consistency problem. The local adaptive nature of the proposed method suppresses the abrupt change in the generated sampling patterns over time, hence ensures a smooth and consistent illumination. By partitioning the spherical surface with simple curvilinear equations, we construct a quadrilateral-based quadtree over the sphere. This Q2-tree allows us to adaptively sample the environment based on an importance metric and generates low-discrepancy sampling patterns. No time-consuming relaxation is required. The sampling patterns of a dynamic sequence are rapidly generated by making use of the summed area table and exploiting the coherence of consecutive frames. From our experiments, the rendering quality of our sampling pattern for a static environment map is comparable to previous methods. However, our method produces smooth and consistent animation for a sequence of dynamic environment maps, even the number of samples is kept constant over time.
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.
Radiance Cache Splatting: A GPU-Friendly Global Illumination Algorithm
(The Eurographics Association, 2005) Gautron, Pascal; Krivánek, Jaroslav; Bouatouch, Kadi; Pattanaik, Sumanta; Kavita Bala and Philip Dutre
Fast global illumination computation is a challenge in several fields such as lighting simulation and computergenerated visual effects for movies. To this end, the irradiance caching algorithm is commonly used since it provides high-quality rendering in a reasonable time. However this algorithm relies on a spatial data structure in which nearest-neighbors queries and data insertions are performed alternately within a single rendering step. Due to this central and permanently modified data structure, the irradiance caching algorithm cannot be easily implemented on graphics hardware. This paper proposes a novel approach to global illumination using irradiance and radiance cache: the radiance cache splatting. This method directly meets the processing constraints of graphics hardware since it avoids the need of complex data structure and algorithms. Moreover, the rendering quality remains identical to classical irradiance and radiance caching. Our renderer shows an implementation of our algorithm which provides a significant speedup compared to classical irradiance caching.

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