Recent approaches to global illumination for dynamic scenes achieve interactive frame-rates by using coarse approximations to geometry, lighting, or both, which limits scene complexity and rendering quality. High-quality global illumination renderings of complex scenes are still limited to methods based on ray tracing. While conceptually simple, these techniques are computationally expensive. We present an efficient and scalable method to compute global illumination solutions at interactive rates for complex and dynamic scenes. It is based on parallel final gathering, running entirely on the GPU. At each final gathering location, we perform micro-rendering: we traverse and rasterize a hierarchical point-based scene representation into an importance-warped micro-buffer, which allows for BRDF importance sampling. The final reflected radiance is computed at each gathering location using the micro-buffers and is then stored in image-space. We can trade quality for speed by reducing the sampling rate of the gathering locations in conjunction with bilateral upsampling. We demonstrate the applicability of our method to interactive global illumination, the simulation of multiple indirect bounces, as well as final gathering from photon maps.

Effective digital content creation tools must be both efficient in the interactions they provide but also allow full user control. There may be occasions, when art direction requires changes that contradict physical laws. In particular, it is known that physical correctness of reflections for the human observer is hard to assess. For many centuries, traditional artists have exploited this fact to depict reflections that lie outside the realm of physical possibility. However, a system that gives explicit control of this effect to digital artists has not yet been described. This paper introduces a system that transforms physically correct reflections into art-directed reflections, as specified by \emph{reflection constraints}. The system introduces a taxonomy of reflection editing operations, using an intuitive user interface, that works directly on the reflecting surfaces with real-time visual feedback using a GPU. A user study shows how such a system can allow users to quickly manipulate reflections according to an art direction task.

In this paper we evaluate the use of approximate visibility for efficient global illumination. Traditionally, accurate visibility is used in light transport. However, the indirect illumination we perceive on a daily basis is rarely of high frequency nature, as the most significant aspect of light transport in real-world scenes is diffuse, and thus displays a smooth gradation. This raises the question of whether accurate visibility is perceptually necessary in this case. To answer this question, we conduct a psychophysical study on the perceptual influence of approximate visibility on indirect illumination. This study reveals that accurate visibility is not required and that certain approximations may be introduced.

Glare is a consequence of light scattered within the human eye when looking at bright light sources. This effect can be exploited for tone mapping since adding glare to the depiction of high-dynamic range (HDR) imagery on a low-dynamic range (LDR) medium can dramatically increase perceived contrast. Even though most, if not all, subjects report perceiving glare as a bright pattern that fluctuates in time, up to now it has only been modeled as a static phenomenon. We argue that the temporal properties of glare are a strong means to increase perceived brightness and to produce realistic and attractive renderings of bright light sources. Based on the anatomy of the human eye, we propose a model that enables real-time simulation of dynamic glare on a GPU. This allows an improved depiction of HDR images on LDR media for interactive applications like games, feature films, or even by adding movement to initially static HDR images. By conducting psychophysical studies, we validate that our method improves perceived brightness and that dynamic glare-renderings are often perceived as more attractive depending on the chosen scene.

Physically plausible illumination at real-time framerates is often achieved using approximations. One popular example is ambient occlusion (AO), for which very simple and efficient implementations are used extensively in production. Recent methods approximate AO between nearby geometry in screen space (SSAO). The key observation described in this paper is, that screen space occlusion methods can be used to compute many more types of effects than just occlusion, such as directional shadows and indirect color bleeding. The proposed generalization has nearly no overhead compared to classic SSAO, approximates direct and one-bounce light transport in screen space, can be combined with other methods that simulate transport for macro structures and is visually equivalent to SSAO in the worst case without introducing new artifacts. Since our method works in screen space, it does not depend on the geometric complexity. Plausible directional occlusion and indirect lighting effects can be displayed for large and fully dynamic scenes at real-time frame rates.

In this paper we present a method for interactive computation of indirect illumination in large and fully dynamic scenes based on approximate visibility queries. While the high-frequency nature of direct lighting requires accurate visibility, indirect illumination mostly consists of smooth gradations, which tend to mask errors due to incorrect visibility. We exploit this by approximating visibility for indirect illumination with imperfect shadow maps --- low-resolution shadow maps rendered from a crude point-based representation of the scene. These are used in conjunction with a global illumination algorithm based on virtual point lights enabling indirect illumination of dynamic scenes at real-time frame rates. We demonstrate that imperfect shadow maps are a valid approximation to visibility, which makes the simulation of global illumination an order of magnitude faster than using accurate visibility.

We present a new approach for enhancing local scene contrast by unsharp masking over arbitrary surfaces under any form of illumination. Our adaptation of a well-known 2D technique to 3D interactive scenarios is designed to aid viewers in tasks like understanding complex or detailed geometric models, medical visualization and navigation in virtual environments. Our holistic approach enhances the depiction of various visual cues, including gradients from surface shading, surface reflectance, shadows, and highlights, to ease estimation of viewpoint, lighting conditions, shapes of objects and their world-space organization. Motivated by recent perceptual findings on 3D aspects of the Cornsweet illusion, we create scene coherent enhancements by treating cues in terms of their 3D context; doing so has a stronger effect than approaches that operate in a 2D image context and also achieves temporal coherence. We validate our unsharp masking in 3D with psychophysical experiments showing that the enhanced images are perceived to have better contrast and are preferred over unenhanced originals. Our operator runs at interactive rates on a GPU and the effect is easily controlled interactively within the rendering pipeline.

Interactive rendering of global illumination effects is a challenging problem. While precomputed radiance transfer (PRT) is able to render such effects in real time the geometry is generally assumed static. This work proposes to replace the precomputed lighting response used in PRT by precomputed depth. Precomputing depth has the same cost as precomputing visibility, but allows visibility tests for moving objects at runtime using simple shadow mapping. For this purpose, a compression scheme for a high number of coherent surface shadow maps (CSSMs) covering the entire scene surface is developed. CSSMs allow visibility tests between all surface points against all points in the scene. We demonstrate the effectiveness of CSSM-based visibility using a novel combination of the lightcuts algorithm and hierarchical radiosity, which can be efficiently implemented on the GPU. We demonstrate interactive n-bounce diffuse global illumination, with a final glossy bounce and many high frequency effects: general BRDFs, texture and normal maps, and local or distant lighting of arbitrary shape and distribution – all evaluated per-pixel. Furthermore, all parameters can vary freely over time – the only requirement is rigid geometry.

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. It supports 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.

Pre-computed radiance transfer (PRT) has been used to render volumetric data under distant low-frequency illumination at real-time rates, including natural illumination, soft shadows, attenuation from semi-transparent occluders and multiple scattering. PRT requires a lengthy pre-process, which is acceptable only for static volume data. However, in practical volume rendering, general transfer functions are used. Manipulating such a transfer function will result in a dynamic radiance transfer which has to be re-computed. This work proposes a fast way for this re-computation. While previous work has used CPU Monte Carlo ray-tracing for pre-computation and requires time in the order of many minutes, our GPU implementation uses a hierarchical visibility approximation implemented entirely on the GPU and requires only a few seconds for typical scenes.

Errata:
Sec. 3.1, 2nd equ.: D_i and D_i+1 should be O_i and O_i+1 (Thanks to Shusen Liu for pointing this out).

Determining the reflectance properties of real materials is an important task for augmented reality applications with consistent illumination. The main application is the insertion of virtual objects with shadows with correct brightness. Moreover, for displaying real objects with user-defined materials, the original materials must be known. Many research results have shown, that a material reconstruction is possible from digital photographs. This reconstruction is often performed under laboratory conditions in a time-consuming pre-process. We present a new method for the on-line reconstruction of diffuse materials given arbitrary, time-varying illumination including soft shadows. Our method uses graphics hardware (GPU) and two high dynamic range (HDR) video cameras to record both the environment and the object.

Mesh painting is a well accepted and very intuitive metaphor for adding high-resolution detail to a given 3D model: Using a brush interface, the designer simply paints fine-scale texture or geometry information onto the surface. In this paper we propose a fully GPU-accelerated mesh painting technique, which provides real-time feedback even for highly complex meshes. Our method can handle arbitrary input meshes, which are considered as base meshes for Catmull-Clark subdivision. Representing the surface by an atlas of geometry images and exploiting programmable vertex and fragment shaders allows for highly efficient LoD rendering and surface manipulation. Our painting metaphor supports real-time texturing, sculpting, smoothing, and multiresolution surface deformations.

Virtuelle Charaktere stellen eine große Herausforderung für die physikalische Simulation, vor allem in Echtzeit, dar. Diese Arbeit stellt der dazu oft verwendeten Starrkörper-Simulationen ein Feder-Masse-System gegenüber. Es wird gezeigt, dass die meisten für Charaktere relevanten physikalischen Erscheinungen bei der Animation von Kleidung, Haaren, Gliedmaßen, Gelenken mit Freiheitsgraden, usw. vereinheitlicht auf ein Feder-Masse-System zurückgeführt werden können. Solche Systeme verhalten sich zwar nicht immer physikalisch exakt, bieten aber dafür höhere Performanz, bessere Skalierbarkeit, einfachere Implementierung und im Rahmen ihrer Möglichkeiten, größere "empfundene" Stabilität. Die einfache Form der Verarbeitung macht eine effiziente Implementierung mit SIMD-Instruktionen möglich, die vorgestellt wird. Das System wird erfolgreich verwendet, um eine "Virtuelle Marionette" mit getrackten Eingabegeräten so zu manipulieren, dass diese in einer virtuellen physikalischen Umgebung einfache Aufgaben (Puzzle, Fußball) lösen kann.