EGSR07: 18th Eurographics Symposium on Rendering

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https://diglib.eg.org/handle/10.2312/386

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Photorealistic Image Rendering with Population Monte Carlo Energy Redistribution
(The Eurographics Association, 2007) Lai, Yu-Chi; Fan, Shao Hua; Chenney, Stephen; Dyer, Charcle; Jan Kautz and Sumanta Pattanaik
This work presents a novel global illumination algorithm which concentrates computation on important light transport paths and automatically adjusts energy distributed area for each light transport path. We adapt statistical framework of Population Monte Carlo into global illumination to improve rendering efficiency. Information collected in previous iterations is used to guide subsequent iterations by adapting the kernel function to approximate the target distribution without introducing bias into the final result. Based on this framework, our algorithm automatically adapts the amount of energy redistribution at different pixels and the area over which energy is redistributed. Our results show that the efficiency can be improved by exploring the correlated information among light transport paths.
Dynamic Point Distribution for Stroke-based Rendering
(The Eurographics Association, 2007) Vanderhaeghe, David; Barla, Pascal; Thollot, Joelle; Sillion, Francois X.; Jan Kautz and Sumanta Pattanaik
We present a new point distribution algorithm that is well adapted to stroke-based rendering systems. Its main characteristic is to deal efficiently with three conflicting constraints: the distribution of points should retain a good repartition in 2D; their motion should tightly follow the target motion in the underlying scene; and as few points as possible should be added or deleted from frame to frame. We show that previous methods fail to meet at least one of these constraints in the general case, as opposed to our approach that is independent of scene complexity and motion. As a result, our algorithm is able to take 3D scenes as well as videos as input and create non-uniform distributions with good temporal coherence and density properties. To illustrate it, we show applications in four different styles: stippling, pointillism, hatching and painterly.
Material Based Splashing of Water Drops
(The Eurographics Association, 2007) Garg, Kshitiz; Krishnan, Gurunandan G.; Nayar, Shree K.; Jan Kautz and Sumanta Pattanaik
The splashing of a water drop is a fascinating phenomenon that results from a variety of complex interactions between the drop and the material it impacts. In general, the distribution of droplets of a splash depends on the drop size and velocity; the surface roughness, rigidity, and wetness; and the angle of impact. Given the number of factors involved, it is difficult to develop an analytical model for the splash distribution. Instead, we take an empirical approach. We have measured the splashing behaviors of 22 different materials that are commonly found in the real world. These materials can be broadly classified as rough (e.g., wood and brick), smooth (e.g., marble and glass), flexible (e.g., silk and paper), and miscellaneous (e.g., water and moss). We have developed a stochastic model for splash distribution that builds upon empirical models previously developed in fluid dynamics and meteorology. Our model is simple and only requires 7 coefficients for generating splashes for head-on impact for a material. A more general model for generating splashes for arbitrary impact angles (due to surface inclination or wind) requires 54 coefficients. The models of different materials may be combined to generate physically plausible splashes for novel materials that have not been measured. Our model is applicable for rendering splashes due to rain as well as water drops falling from large heights such as windowsills, trees, and rooftops.
Incremental Instant Radiosity for Real-Time Indirect Illumination
(The Eurographics Association, 2007) Laine, Samuli; Saransaari, Hannu; Kontkanen, Janne; Lehtinen, Jaakko; Aila, Timo; Jan Kautz and Sumanta Pattanaik
We present a method for rendering single-bounce indirect illumination in real time on currently available graphics hardware. The method is based on the instant radiosity algorithm, where virtual point lights (VPLs) are generated by casting rays from the primary light source. Hardware shadow maps are then employed for determining the indirect illumination from the VPLs. Our main contribution is an algorithm for reusing the VPLs and incrementally maintaining their good distribution. As a result, only a few shadow maps need to be rendered per frame as long as the motion of the primary light source is reasonably smooth. This yields real-time frame rates even when hundreds of VPLs are used.
Microfacet Models for Refraction through Rough Surfaces
(The Eurographics Association, 2007) Walter, Bruce; Marschner, Stephen R.; Li, Hongsong; Torrance, Kenneth E.; Jan Kautz and Sumanta Pattanaik
Microfacet models have proven very successful for modeling light reflection from rough surfaces. In this paper we review microfacet theory and demonstrate how it can be extended to simulate transmission through rough surfaces such as etched glass. We compare the resulting transmission model to measured data from several real surfaces and discuss appropriate choices for the microfacet distribution and shadowing-masking functions. Since rendering transmission through media requires tracking light that crosses at least two interfaces, good importance sampling is a practical necessity. Therefore, we also describe efficient schemes for sampling the microfacet models and the corresponding probability density functions.
Feature-Guided Dynamic Texture Synthesis on Continuous Flows
(The Eurographics Association, 2007) Narain, Rahul; Kwatra, Vivek; Lee, Huai-Ping; Kim, Theodore; Carlson, Mark; Lin, Ming C.; Jan Kautz and Sumanta Pattanaik
We present a technique for synthesizing spatially and temporally varying textures on continuous flows using image or video input, guided by the physical characteristics of the fluid stream itself. This approach enables the generation of realistic textures on the fluid that correspond to the local flow behavior, creating the appearance of complex surface effects, such as foam and small bubbles. Our technique requires only a simple specification of texture behavior, and automatically generates and tracks the features and texture over time in a temporally coherent manner. Based on this framework, we also introduce a technique to perform feature-guided video synthesis. We demonstrate our algorithm on several simulated and recorded natural phenomena, including splashing water and lava flows. We also show how our methodology can be extended beyond realistic appearance synthesis to more general scenarios, such as temperature-guided synthesis of complex surface phenomena in a liquid during boiling.
Rendering Translucent Materials Using Photon Diffusion
(The Eurographics Association, 2007) Donner, Craig; Jensen, Henrik Wann; Jan Kautz and Sumanta Pattanaik
We present a new algorithm for rendering translucent materials that combines photon tracing with diffusion. This combination makes it possible to efficiently render highly scattering translucent materials while accounting for internal blockers, complex geometry, translucent inter-scattering, and transmission and refraction of light at the boundary causing internal caustics. These effects cannot be accounted for with previous rendering approaches using the dipole or multipole diffusion approximations that only sample the incident illumination at the surface of the material. Instead of sampling lighting at the surface we trace photons into the material and store them volumetrically at their first scattering interaction with the material. We hierarchically integrate the diffusion of light from the photons to compute the radiant emittance at points on the surface of the material. For increased accuracy we use the incidence plane of the photon and the viewpoint on the surface to blend between three analytic diffusion approximations that best describe the geometric configuration between the photon and the shading point. For this purpose we introduce a new quadpole diffusion approximation that models diffusion at right angled edges, and an attenuation kernel to more accurately model multiple scattering near a light source. The photon diffusion approach is as efficient as previous Monte Carlo sampling approaches based on the dipole or multipole diffusion approximations, and our results demonstrate that it is more accurate and capable of capturing several illumination effects previously ignored when simulating the diffusion of light in translucent materials.
Rendering Discrete Random Media Using Precomputed Scattering Solutions
(The Eurographics Association, 2007) Moon, Jonathan T.; Walter, Bruce; Marschner, Stephen R.; Jan Kautz and Sumanta Pattanaik
This paper addresses light transport through a discrete random medium, which we define as a volume filled with macroscopic scattering geometry generated by a random process. This formulation is more general than standard radiative transport, because it can be applied to media that are made up of closely packed scatterers. A new approach to rendering these media is introduced, based on precomputed solutions to a local multiple scattering problem, including a new algorithm for generating paths through random media that moves through the interior of the medium in large strides without considering individual scattering events. A method for rendering homogeneous isotropic random media is described that generates paths using precomputed scattering solutions compressed and randomly sampled using Nonnegative Matrix Factorization. It can efficiently render discrete media, such as a large pile of glass objects, in which the individual scatterers are visible. The method is demonstrated on scenes containing tens of thousands of transparent, specular objects that are nearly impossible to render with standard global illumination techniques.
Whitted Ray-Tracing for Dynamic Scenes using a Ray-Space Hierarchy on the GPU
(The Eurographics Association, 2007) Roger, David; Assarsson, Ulf; Holzschuch, Nicolas; Jan Kautz and Sumanta Pattanaik
In this paper, we present a new algorithm for interactive rendering of animated scenes with Whitted Ray-Tracing, running on the GPU. We focus our attention on the secondary rays (the rays generated by one or more bounces on specular objects), and use the GPU rasterizer for primary rays. Our algorithm is based on a ray-space hierarchy, allowing us to handle truly dynamic scenes without the need to rebuild or update the scene hierarchy. The rayspace hierarchy is entirely built on the GPU for every frame, using a very fast process. Traversing the ray-space hierarchy is also done on the GPU; one of the benefits of using a ray-space hierarchy is that we have a single shader, and a fixed number of passes. After traversing each level of the hierarchy, we prune empty branches using a stream reduction method. We present two different stream reduction methods, a fast one using a hierarchical algorithm, and an easy one using the Geometry shaders. Our algorithm results in interactive rendering with specular reflections and shadows for moderately complex scenes (~ 700K triangles), handles any kind of dynamic or unstructured scenes without any pre-processing, and scales well with both the scene complexity and the image resolution.
Soft Shadows by Ray Tracing Multilayer Transparent Shadow Maps
(The Eurographics Association, 2007) Xie, Feng; Tabellion, Eric; Pearce, Andrew; Jan Kautz and Sumanta Pattanaik
We present a method for high quality soft shadows for area lights in cinematic lighting. The method is an extension of traditional shadow maps, so it has the advantage of image based shadow methods; the algorithm s complexity is independent of geometric complexity. We introduce multilayer transparent shadow maps, which can be used to produce high quality soft shadows for scenes with extremely complex geometry, fur, and volume objects. Instead of the traditional sampling and filtering of shadow maps, we compute the shadow factor by ray tracing the multilayer transparent shadow map. The result is soft shadows of quality similar to that achieved by stochastic ray tracing, but at a much lower cost.
Scene Collages and Flexible Camera Arrays
(The Eurographics Association, 2007) Nomura, Yoshikuni; Zhang, Li; Nayar, Shree K.; Jan Kautz and Sumanta Pattanaik
This paper presents an automatic method for creating a collage from a collection of photos of a scene taken from different viewpoints. The collage is constructed by aligning the images (in terms of their positions, rotations and scales) using a least-squares formulation. We have developed a graph-based optimization algorithm for layering the images so as to minimize the fragmentation of the collage. A collage can be displayed with opaque layers, with transparent layers, or with blended image boundaries. A scene collage can be viewed as a piece-wise perspective representation of a scene with visible seams. This representation has not only aesthetic value but also conveys scene structure and camera motion in an intuitive way. To capture live-action collages of dynamic scenes we have developed camera arrays that can be physically flexed by the user to continuously vary the composition of the scene. The design of our camera arrays enables a user to reconfigure them in terms of the spatial arrangement of the cameras in a matter of minutes. We show several still and dynamic examples that demonstrate that scene collages provide a new and interesting way to experience scenes.
Natural Image Colorization
(The Eurographics Association, 2007) Luan, Qing; Wen, Fang; Cohen-Or, Daniel; Liang, Lin; Xu, Ying-Qing; Shum, Heung-Yeung; Jan Kautz and Sumanta Pattanaik
In this paper, we present an interactive system for users to easily colorize the natural images of complex scenes. In our system, colorization procedure is explicitly separated into two stages: Color labeling and Color mapping. Pixels that should roughly share similar colors are grouped into coherent regions in the color labeling stage, and the color mapping stage is then introduced to further fine-tune the colors in each coherent region. To handle textures commonly seen in natural images, we propose a new color labeling scheme that groups not only neighboring pixels with similar intensity but also remote pixels with similar texture. Motivated by the insight into the complementary nature possessed by the highly contrastive locations and the smooth locations, we employ a smoothness map to guide the incorporation of intensity-continuity and texture-similarity constraints in the design of our labeling algorithm. Within each coherent region obtained from the color labeling stage, the color mapping is applied to generate vivid colorization effect by assigning colors to a few pixels in the region. A set of intuitive interface tools is designed for labeling, coloring and modifying the result. We demonstrate compelling results of colorizing natural images using our system, with only a modest amount of user input.
Interactive Illumination with Coherent Shadow Maps
(The Eurographics Association, 2007) Ritschel, Tobias; Grosch, Thorsten; Kautz, Jan; Mueller, Stefan; Jan Kautz and Sumanta Pattanaik
We present a new method for interactive illumination computations based on precomputed visibility using coherent shadow maps (CSMs). It is well-known that visibility queries dominate the cost of physically based rendering. Precomputing all visibility events, for instance in the form of many shadow maps, enables fast queries and allows for real-time computation of illumination but requires prohibitive amounts of storage. We propose a lossless compression scheme for visibility information based on shadow maps that efficiently exploits coherence. We demonstrate a Monte Carlo renderer for direct lighting using CSMs that runs entirely on graphics hardware. We support spatially varying BRDFs, normal maps, and environment maps all with high frequencies, spatial as well as angular. Multiple dynamic rigid objects can be combined in a scene. As opposed to precomputed radiance transfer techniques, that assume distant lighting, our method includes distant lighting as well as local area lights of arbitrary shape, varying intensity, or anisotropic light distribution that can freely vary over time.
Dirty Glass: Rendering Contamination on Transparent Surfaces
(The Eurographics Association, 2007) Gu, Jinwei; Ramamoorthi, Ravi; Belhumeur, Peter; Nayar, Shree; Jan Kautz and Sumanta Pattanaik
Rendering of clean transparent objects has been well studied in computer graphics. However, real-world transparent objects are seldom clean their surfaces have a variety of contaminants such as dust, dirt, and lipids. These contaminants produce a number of complex volumetric scattering effects that must be taken into account when creating photorealistic renderings. In this paper, we take a step toward modeling and rendering these effects. We make the assumption that the contaminant is an optically thin layer and construct an analytic model following results in radiative transport theory and computer graphics. Moreover, the spatial textures created by the different types of contamination are also important in achieving visual realism. To this end, we measure the spatially varying thicknesses and the scattering parameters of a number of glass panes with various types of dust, dirt, and lipids. We also develop a simple interactive synthesis tool to create novel instances of the measured contamination patterns. We show several results that demonstrate the use of our scattering model for rendering 3D scenes, as well as modifying real 2D photographs.
General Linear Cameras with Finite Aperture
(The Eurographics Association, 2007) Adams, Andrew; Levoy, Marc; Jan Kautz and Sumanta Pattanaik
A pinhole camera selects a two-dimensional set of rays from the four-dimensional light field. Pinhole cameras are a type of general linear camera, defined as planar 2D slices of the 4D light field. Cameras with finite apertures can be considered as the summation of a collection of pinhole cameras. In the limit they evaluate a two-dimensional integral of the four-dimensional light field. Hence a general linear camera with finite aperture factors the 4D light field into two integrated dimensions and two imaged dimensions. We present a simple framework for representing these slices and integral projections, based on certain eigenspaces in a two-plane parameterization of the light field. Our framework allows for easy analysis of focus and perspective, and it demonstrates their dual nature. Using our framework, we present analogous taxonomies of perspective and focus, placing within them the familiar perspective, orthographic, cross-slit, and bilinear cameras; astigmatic and anastigmatic focus; and several other varieties of perspective and focus.
Procedural Editing of Bidirectional Texture Functions
(The Eurographics Association, 2007) Mueller, Gero; Sarlette, Ralf; Klein, Reinhard; Jan Kautz and Sumanta Pattanaik
Measured material representations like Bidirectional Texture Functions or Reflectance Fields offer very realistic appearance but the user is currently not capable of changing this appearance in an effective and intuitive way. Such editing operations would require a low-dimensional but expressive model for appearance that exposes only a small set of intuitively editable parameters (1D-sliders, 2D-maps) to the user but preserves all visually relevant details. In this paper we present a novel editing technique for complex spatially varying materials. It is based on the observation that we are already good in modeling the basic geometric structure of many natural and manmade materials but still have not found effective models for the detailed small-scale geometry and the interaction of light with these materials. Our main idea is to use procedural geometry to define the basic structure of a material and then to enrich this structure with the BTF information captured from real materials. By employing recent algorithms for real-time texture synthesis and BTF compression our technique allows interactive editing.
Instant Sound Scattering
(The Eurographics Association, 2007) Tsingos, Nicolas; Dachsbacher, Carsten; Lefebvre, Sylvain; Dellepiane, Matteo; Jan Kautz and Sumanta Pattanaik
Real-time sound rendering engines often render occlusion and early sound reflection effects using geometrical techniques such as ray or beam tracing. They can only achieve interactive rendering for environments of low local complexity resulting in crude effects which can degrade the sense of immersion. However, surface detail or complex dynamic geometry has a strong influence on sound propagation and the resulting auditory perception. This paper focuses on high-quality modeling of first-order sound scattering. Based on a surface-integral formulation and the Kirchhoff approximation, we propose an efficient evaluation of scattering effects, including both diffraction and reflection, that leverages programmable graphics hardware for dense sampling of complex surfaces. We evaluate possible surface simplification techniques and show that combined normal and displacement maps can be successfully used for audio scattering calculations. We present an auralization framework that can render scattering effects interactively thus providing a more compelling experience. We demonstrate that, while only considering first order phenomena, our approach can provide realistic results for a number of practical interactive applications. It can also process highly detailed models containing millions of unorganized triangles in minutes, generating high-quality scattering filters. Resulting simulations compare well with on-site recordings showing that the Kirchhoff approximation can be used for complex scattering problems.
Large-Scale Data Management for PRT-Based Real-Time Rendering of Dynamically Skinned Models
(The Eurographics Association, 2007) Feng, Wei-Wen; Peng, Liang; Jia, Yuntao; Yu, Yizhou; Jan Kautz and Sumanta Pattanaik
Computer games and real-time applications frequently adopt mesh skinning as a deformation technique for virtual characters and articulated objects. Rendering skinned models with global shading effects, such as interreflection and subsurface scattering, using precomputed radiance transfer enables high-quality real-time display of dynamically deformed objects. In this approach, we need to precompute radiance transfer for many sampled poses. Resulting datasets reach hundreds of gigabytes, and are orders of magnitude larger than those for a static object. This paper presents simple but effective large-scale data management techniques so that runtime data communication, decompression and interpolation can be performed efficiently and accurately. Specifically, we have developed a mesh clustering technique based on spectral graph partitioning to facilitate interpolation from nearest neighbors and an incremental clustering method for transfer matrix compression. By exploiting additional data redundancies among different sampled poses, we can achieve higher compression ratios with the same fidelity. Our incremental clustering can make the runtime cost of per-frame data decompression and interpolation satisfy a prescribed upper bound. As a result, we can achieve real-time performance using the massive precomputed data and an efficient runtime algorithm.
High Dynamic Range Image Hallucination
(The Eurographics Association, 2007) Wang, Lvdi; Wei, Li-Yi; Zhou, Kun; Guo, Baining; Shum, Heung-Yeung; Jan Kautz and Sumanta Pattanaik
We introduce high dynamic range image hallucination for adding high dynamic range details to the over-exposed and under-exposed regions of a low dynamic range image. Our method is based on a simple assumption: there exist high quality patches in the image with similar textures as the regions that are over or under exposed. Hence, we can add high dynamic range details to a region by simply transferring texture details from another patch that may be under different illumination levels. In our approach, a user only needs to annotate the image with a few strokes to indicate textures that can be applied to the corresponding under-exposed or over-exposed regions, and these regions are automatically hallucinated by our algorithm. Experiments demonstrate that our simple, yet effective approach is able to significantly increase the amount of texture details in a wide range of common scenarios, with a modest amount of user interaction.
Interactive Smooth and Curved Shell Mapping
(The Eurographics Association, 2007) Jeschke, Stefan; Mantler, Stephan; Wimmer, Michael; Jan Kautz and Sumanta Pattanaik
Shell mapping is a technique to represent three-dimensional surface details. This is achieved by extruding the triangles of an existing mesh along their normals, and mapping a 3D function (e.g., a 3D texture) into the resulting prisms. Unfortunately, such a mapping is nonlinear. Previous approaches perform a piece-wise linear approximation by subdividing the prisms into tetrahedrons. However, such an approximation often leads to severe artifacts. In this paper we present a correct (i.e., smooth) mapping that does not rely on a decomposition into tetrahedrons. We present an efficient GPU ray casting algorithm which provides correct parallax, self-occlusion, and silhouettes, at the cost of longer rendering times. The new formulation also allows modeling shells with smooth curvatures using Coons patches within the prisms. Tangent continuity between adjacent prisms is guaranteed, while the mapping itself remains local, i.e. every curved prism content is modeled at runtime in the GPU without the need for any precomputation. This allows instantly replacing animated triangular meshes with prism-based shells.

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