EGSR06: 17th Eurographics Symposium on Rendering

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https://diglib.eg.org/handle/10.2312/385

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Ardeco: Automatic Region DEtection and COnversion
(The Eurographics Association, 2006) Lecot, Gregory; Levy, Bruno; Tomas Akenine-Moeller and Wolfgang Heidrich
We present Ardeco, a new algorithm for image abstraction and conversion from bitmap images into vector graphics. Given a bitmap image, our algorithm automatically computes the set of vector primitives and gradients that best approximates the image. In addition, more details can be generated in user-selected important regions, defined from eye-tracking data or from an importance map painted by the user. Our algorithm is based on a new two-level variational parametric segmentation algorithm, minimizing Mumford and Shah s energy and operating on an intermediate triangulation, well adapted to the features of the image.
Exploiting Temporal Coherence for Incremental All-Frequency Relighting
(The Eurographics Association, 2006) Overbeck, Ryan; Ben-Artzi, Aner; Ramamoorthi, Ravi; Grinspun, Eitan; Tomas Akenine-Moeller and Wolfgang Heidrich
Precomputed radiance transfer (PRT) enables all-frequency relighting with complex illumination, materials and shadows. To achieve real-time performance, PRT exploits angular coherence in the illumination, and spatial coherence in the light transport. Temporal coherence of the lighting from frame to frame is an important, but unexplored additional form of coherence for PRT. In this paper, we develop incremental methods for approximating the differences in lighting between consecutive frames. We analyze the lighting wavelet decomposition over typical motion sequences, and observe differing degrees of temporal coherence across levels of the wavelet hierarchy. To address this, our algorithm treats each level separately, adapting to available coherence. The proposed method is orthogonal to other forms of coherence, and can be added to almost any all-frequency PRT algorithm with minimal implementation, computation or memory overhead. We demonstrate our technique within existing codes for nonlinear wavelet approximation, changing view with BRDF factorization, and clustered PCA. Exploiting temporal coherence of dynamic lighting yields a 3×-4× performance improvement, e.g., all-frequency effects are achieved with 30 wavelet coefficients per frame for the lighting, about the same as low-frequency spherical harmonic methods. Distinctly, our algorithm smoothly converges to the exact result within a few frames of the lighting becoming static.
A Spectral BSSRDF for Shading Human Skin
(The Eurographics Association, 2006) Donner, Craig; Jensen, Henrik Wann; Tomas Akenine-Moeller and Wolfgang Heidrich
We present a novel spectral shading model for human skin. Our model accounts for both subsurface and surface scattering, and uses only four parameters to simulate the interaction of light with human skin. The four parameters control the amount of oil, melanin and hemoglobin in the skin, which makes it possible to match specific skin types. Using these parameters we generate custom wavelength dependent diffusion profiles for a two-layer skin model that account for subsurface scattering within the skin. These diffusion profiles are computed using convolved diffusion multipoles, enabling an accurate and rapid simulation of the subsurface scattering of light within skin. We combine the subsurface scattering simulation with a Torrance-Sparrow BRDF model to simulate the interaction of light with an oily layer at the surface of the skin. Our results demonstrate that this four parameter model makes it possible to simulate the range of natural appearance of human skin including African, Asian, and Caucasian skin types.
Adaptive Visibility-Driven View Cell Construction
(The Eurographics Association, 2006) Mattausch, Oliver; Bittner, Jirí; Wimmer, Michael; Tomas Akenine-Moeller and Wolfgang Heidrich
We present a new method for the automatic partitioning of view space into a multi-level view cell hierarchy. We use a cost-based model in order to minimize the average rendering time. Unlike previous methods, our model takes into account the actual visibility in the scene, and the partition is not restricted to planes given by the scene geometry. We show that the resulting view cell hierarchy works for different types of scenes and gives lower average rendering time than previously used methods.
Real-time Multi-perspective Rendering on Graphics Hardware
(The Eurographics Association, 2006) Hou, Xianyou; Wei, Li-Yi; Shum, Heung-Yeung; Guo, Baining; Tomas Akenine-Moeller and Wolfgang Heidrich
Multi-perspective rendering has a variety of applications; examples include lens refraction, curved mirror re- flection, caustics, as well depiction and visualization. However, multi-perspective rendering is not yet practical on polygonal graphics hardware, which so far has utilized mostly single-perspective (pin-hole or orthographic) projections. In this paper, we present a methodology for real-time multi-perspective rendering on polygonal graphics hardware. Our approach approximates a general multi-perspective projection surface (such as a curved mirror and lens) via a piecewise-linear triangle mesh, upon which each triangle is a simple multi-perspective camera, parameterized by three rays at triangle vertices. We derive analytic formula showing that each triangle projection can be implemented as a pair of vertex and fragment programs on programmable graphics hardware. We demonstrate real-time performance of a variety of applications enabled by our technique, including reflection, refraction, caustics, and visualization.
Texture Replacement of Garments in Monocular Video
(The Eurographics Association, 2006) Scholz, Volker; Magnor, Marcus; Tomas Akenine-Moeller and Wolfgang Heidrich
In this paper, we present a video processing algorithm for texture replacement of moving garments in monocular video recordings. We use a color-coded pattern which encodes texture coordinates within a local neighborhood in order to determine the geometric deformation of the texture. A time-coherent texture interpolation is obtained by the use of 3D radial basis functions. Shading maps are determined with a surface reconstruction technique and applied to new textures which replace the color pattern in the video sequence. Our method enables exchanging fabric pattern designs of garments worn by actors as a video post-processing step.
Ambient Occlusion for Animated Characters
(The Eurographics Association, 2006) Kontkanen, Janne; Aila, Timo; Tomas Akenine-Moeller and Wolfgang Heidrich
We present a novel technique for approximating ambient occlusion of animated objects. Our method automatically determines the correspondence between animation parameters and per-vertex ambient occlusion using a set of reference poses as its input. Then, at runtime, the ambient occlusion is approximated by taking a dot product between the current animation parameters and static per-vertex coefficients. According to our results, both the computational and storage requirements are low enough for the technique to be directly applicable to computer games running on current graphics hardware. The resulting images are also significantly more realistic than the commonly used static ambient occlusion solutions.
A GPU-driven Algorithm for Accurate Interactive Reflections on Curved Objects
(The Eurographics Association, 2006) Estalella, Pau; Martin, Ignacio; Drettakis, George; Tost, Dani; Tomas Akenine-Moeller and Wolfgang Heidrich
We present a GPU-driven method for the fast computation of specular reflections on curved objects. For every reflector of the scene, our method computes a virtual object for every other object reflected in it. This virtual reflected object is then rendered and blended with the scene. For each vertex of each virtual object, a reflection point is found on the reflector s surface. This point is used to find the reflected virtual vertex, enabling the reflected virtual scene to be rendered. Our method renders the 3D points and normals of the reflector into textures, and uses a local search in a fragment program on the GPU to find the reflection points. By reorganizing the data and the computation in this manner, and correctly treating special cases, we make excellent use of the parallelism and stream-processing power of the GPU. In our results we show that, with our method, we can display high-quality reflections of nearby objects interactively.
Image-driven Navigation of Analytical BRDF Models
(The Eurographics Association, 2006) Ngan, Addy; Durand, Frédo; Matusik, Wojciech; Tomas Akenine-Moeller and Wolfgang Heidrich
Specifying parameters of analytic BRDF models is a difficult task as these parameters are often not intuitive for artists and their effect on appearance can be non-uniform. Ideally, a given step in the parameter space should produce a predictable and perceptually-uniform change in the rendered image. Systems that employ psychophysics have produced important advances in this direction; however, the requirement of user studies limits scalability of these approaches. In this work, we propose a new and intuitive method for designing material appearance. First, we define a computational metric between BRDFs that is based on rendered images of a scene under natural illumination. We show that our metric produces results that agree with previous perceptual studies. Next, we propose a user interface that allows for navigation in the remapped parameter space of a given BRDF model. For the current settings of the BRDF parameters, we display a choice of variations corresponding to uniform steps according to our metric, in the various parameter directions. In addition to the parametric navigation for a single model, we also support neighborhood navigation in the space of all models. By clustering a large number of neighbors and removing neighbors that are close to the current model, the user can easily visualize the alternate effects that can only be expressed with other models. We show that our interface is simple and intuitive. Furthermore, visual navigation in the BRDF space both in the local model and the union space is an effective way for reflectance design.
Making Radiance and Irradiance Caching Practical: Adaptive Caching and Neighbor Clamping
(The Eurographics Association, 2006) Krivánek, Jaroslav; Bouatouch, Kadi; Pattanaik, Sumanta; Zára, Jirí; Tomas Akenine-Moeller and Wolfgang Heidrich
Radiance and irradiance caching are efficient global illumination algorithms based on interpolating indirect illumination from a sparse set of cached values. In this paper we propose an adaptive algorithm for guiding spatial density of the cached values in radiance and irradiance caching. The density is adapted to the rate of change of indirect illumination in order to avoid visible interpolation artifacts and produce smooth interpolated illumination. In addition, we discuss some practical problems arising in the implementation of radiance and irradiance caching, and propose techniques for solving those problems. Namely, the neighbor clamping heuristic is proposed as a robust means for detecting small sources of indirect illumination and for dealing with problems caused by ray leaking through small gaps between adjacent polygons.
Bidirectional Instant Radiosity
(The Eurographics Association, 2006) Segovia, Benjamin; Iehl, Jean Claude; Mitanchey, Richard; Péroche, Bernard; Tomas Akenine-Moeller and Wolfgang Heidrich
This paper presents a new sampling strategy to achieve interactive global illumination on one commodity computer. The goal is to propose an efficient numerical stochastic scheme which can be well adapted to a fast rendering algorithm. As we want to provide an efficient sampling strategy to handle difficult settings without sacrificing performance in common cases, we developed an extension of Instant Radiosity [Kel97] in the same way bidirectional path tracing is an extension of path or light tracing. Our idea is to build several estimators and to efficiently combine them to find a set of virtual point light sources which are relevant for the areas of the scene seen by the camera. The resulting algorithm is faster than classical solutions to global illumination. Using today graphics hardware, an interactive frame rate and the convergence of the scheme can be easily obtained in scenes with many light sources, glossy materials or difficult visibility problems.
Practical, Real-time Studio Matting using Dual Imagers
(The Eurographics Association, 2006) McGuire, Morgan; Matusik, Wojciech; Yerazunis, William; Tomas Akenine-Moeller and Wolfgang Heidrich
This paper presents a practical system for capturing high-resolution video mattes using cameras that contain two imagers on one optical axis. The dual imagers capture registered frames that differ only by defocus or polarization at pixels corresponding to special background gray-screens. This system eliminates color spill and other drawbacks of blue-screen matting while preserving many of its desirable properties (e.g., unassisted, real-time, natural illumination) over more recent methods, and achieving higher precision output for Bayer-filter digital cameras. Because two imagers capture more information than one, we are able to automatically process scenes that would require manual retouching with blue- screen matting. The dual-imager system successfully pulls mattes for scenes containing thin hair, liquids, glass, and reflective objects; mirror reflections produce incorrect results. We show result comparisons for these scenes against blue-screen matting and describe materials and patterns for building a capture system.
Visual Chatter in the Real World
(The Eurographics Association, 2006) Nayar, Shree K.; Krishnan, Gurunandan G.; Tomas Akenine-Moeller and Wolfgang Heidrich
When a scene is lit by a source of light, the radiance of each point in the scene can be viewed as having two components, namely, direct and global. Recently, an efFIcient separation method has been proposed that uses high frequency illumination patterns to measure the direct and global components of a scene. The global component could arise from not only interreflections but also subsurface scattering within translucent surfaces and volumetric scattering by participating media. In this paper, we use this method to measure the direct and global components of a variety of natural and man-made materials. The computed direct and global images provide interesting insights into the scattering properties of common real-world materials. We have also measured the two components for a 3D texture as a function of lighting direction. This experiment shows that the global component of a BTF tends vary smoothly with respect to the lighting direction compared to the direct component of the BTF. Finally, we apply the separation method to a translucent object for different imaging and illumination scales (resolutions). The results obtained show how the BSSDRF of the object gradually reduces to a BRDF as one goes from fine to coarse scale. All the measurement results reported here, as well as several others, can be viewed as high resolution images at http://www1.cs.columbia.edu/CAVE/projects/separation/separation.php.
Segmentation-Based 3D Artistic Rendering
(The Eurographics Association, 2006) Kolliopoulos, Alexander; Wang, Jack M.; Hertzmann, Aaron; Tomas Akenine-Moeller and Wolfgang Heidrich
This paper introduces segmentation-based 3D non-photorealistic rendering, in which 3D scenes are rendered as a collection of 2D image segments. Segments abstract out unnecessary detail and provide a basis for defining new rendering styles. These segments are computed by a spectral clustering algorithm that incorporates 3D information, including depth, user-defined importance, and object grouping. Temporally coherent animation is created by biasing adjacent frames to have similar segmentations. We describe algorithms for rendering segments in styles inspired by a number of hand-painted images.
Two Stage Importance Sampling for Direct Lighting
(The Eurographics Association, 2006) Cline, David; Egbert, Parris K.; Talbot, Justin F.; Cardon, David L.; Tomas Akenine-Moeller and Wolfgang Heidrich
We describe an importance sampling method to generate samples based on the product of a BRDF and an environment map or large light source. The method works by creating a hierarchical partition of the light source based on the BRDF function for each primary (eye) ray in a ray tracer. This partition, along with a summed area table of the light source, form an approximation to the product function that is suitable for importance sampling. The partition is used to guide a sample warping algorithm to transform a uniform distribution of points so that they approximate the product distribution. The technique is unbiased, requires little precomputation, and we demonstrate that it works well for a variety of BRDF types. Further, we present an adaptive method which allocates varying numbers of samples to different image pixels to reduce shadow artifacts.
Painting With Texture
(The Eurographics Association, 2006) Ritter, Lincoln; Li, Wilmot; Curless, Brian; Agrawala, Maneesh; Salesin, David; Tomas Akenine-Moeller and Wolfgang Heidrich
We present an interactive texture painting system that allows the user to author digital images by painting with a palette of input textures. At the core of our system is an interactive texture synthesis algorithm that generates textures with natural-looking boundary effects and alpha information as the user paints. Furthermore, we describe an intuitive layered painting model that allows strokes of texture to be merged, intersected and overlapped while maintaining the appropriate boundaries between texture regions. We demonstrate the utility and expressiveness of our system by painting several images using textures that exhibit a range of different boundary effects.
Surface Enhancement Using Real-time Photometric Stereo and Reflectance Transformation
(The Eurographics Association, 2006) Malzbender, Tom; Wilburn, Bennett; Gelb, Dan; Ambrisco, Bill; Tomas Akenine-Moeller and Wolfgang Heidrich
Photometric stereo recovers per-pixel estimates of surface orientation from images of a surface under varying lighting conditions. Transforming reflectance based on recovered normal directions is useful for enhancing the appearance of subtle surface detail. We present the first system that achieves real-time photometric stereo and reflectance transformation. A high-speed video camera, computer controlled light sources and fast GPU implementations of the algorithms enable both methods. We also present novel GPU-accelerated normal transformations before relighting that "amplify" shape detail. By applying standard image processing methods to our computed normal image, we can selectively enhance surface detail at different frequencies. Our system allows users in fields such as forensics, archeology and dermatology to investigate objects and surfaces by simply holding them in front of the camera. Real-time analysis of surface roughness for metrology can also be performed from the extracted normal field.
Reconstruction of Volumetric Surface Textures for Real-Time Rendering
(The Eurographics Association, 2006) Magda, Sebastian; Kriegman, David; Tomas Akenine-Moeller and Wolfgang Heidrich
Volumetric texturing is a popular technique for rendering rich 3-D detail when a polygonal surface representation would be ineffective. Although efficient algorithms for rendering volumetric textures have been known for years, capturing the richness of a real-life volumetric materials remains a challenging problem. In this paper we propose a technique for generating a volumetric representation of a complex 3-D texture with unknown reflectance and structure. From acquired reflectance data in the form of a 6-D Bidirectional Texture Function (BTF), the proposed algorithm creates an efficient volumetric representation in the form of a stack of semi-transparent layers each representing a slice through the texture s volume. In addition to negligible storage requirements, this representation is ideally suited for hardware-accelerated real-time rendering.
A Novel Method for Fast and High-Quality Rendering of Hair
(The Eurographics Association, 2006) Xu, Songhua; Lau, Francis C. M.; Jiang, Hao; Pan, Yunhe; Tomas Akenine-Moeller and Wolfgang Heidrich
This paper proposes a new rendering approach for hair. The model we use incorporates semantics-related information directly in the appearance modeling function which we call a Semantics-Aware Texture Function (SATF). This new appearance modeling function is well suited for constructing an off-line/on-line hybrid algorithm to achieve fast and high-quality rendering of hair. The off-line phase generates intermediate results in a database for sample geometries under different viewing and lighting conditions, which can be used to complete a large part of the overall computation and leaves only a few dynamic tasks to be performed on-line. We propose a model having four levels, from the whole hair volume to the very fine hair density level. We further employ an efficient disk-like structure to represent hair distributions inside a hair cluster. As the intermediate database carries opacity information, self-shadows can be easily generated. We present experiment results which clearly show that our methodology can indeed produce high quality rendering results efficiently. Supplementary materials and supporting demos can be found in our project website http://www.cs.hku.hk/~songhua/hair-rendering/.
Instant Ray Tracing: The Bounding Interval Hierarchy
(The Eurographics Association, 2006) Wächter, Carsten; Keller, Alexander; Tomas Akenine-Moeller and Wolfgang Heidrich
We introduce a new ray tracing algorithm that exploits the best of previous methods: Similar to bounding volume hierarchies the memory of the acceleration data structure is linear in the number of objects to be ray traced and can be predicted prior to construction, while the traversal of the hierarchy is as efficient as the one of kd-trees. The construction algorithm can be considered a variant of quicksort and for the first time is based on a global space partitioning heuristic, which is much cheaper to evaluate than the classic surface area heuristic. Compared to spatial partitioning schemes only a fraction of the memory is used and a higher numerical precision is intrinsic. The new method is simple to implement and its high performance is demonstrated by extensive measurements including massive as well as dynamic scenes, where we focus on the total time to image including the construction cost rather than on only frames per second.

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