VMV: Vision, Modeling, and Visualization

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The Bounced Z-buffer for Indirect Visibility
(The Eurographics Association, 2015) Nalbach, Oliver; Ritschel, Tobias; Seidel, Hans-Peter; David Bommes and Tobias Ritschel and Thomas Schultz
Synthesizing images of animated scenes with indirect illumination and glossy materials at interactive frame rates commonly ignores indirect shadows. In this work we extend a class of indirect lighting algorithms that splat shading to a framebuffer - we demonstrate deep screen space and ambient occlusion volumes - to include indirect visibility. To this end we propose the bounced z-buffer: While a common z-buffered framebuffer, at each pixel, maintains the distance from the closest surface and its radiance along a direction from the camera to that pixel, our new representation contains the distance from the closest surface and its radiance after one indirect bounce into a certain other direction. Consequently, with bounced z-buffering, only the splat from the nearest emitter in one direction contributes to each pixel. Importance-sampling the bounced directions according to the product of cosine term and BRDF allows to approximate full shading by a simple sum of neighboring framebuffer pixels.
A Deferred Rendering Pipeline Including a Global Illumination Model for Atmospheric Scattering and Transparency
(The Eurographics Association, 2016) Heppner, S.; Dransfeld, M.; Domik, G.; Oleg Lobachev
Abstract This poster presents suitable global illumination models for atmospheric scattering in outdoor scenes combined with a deferred rendering pipeline which offers the possibility of rendering transparent objects. The use case is a HIL simulation for camera based ADAS tests that require a realistic rendering of outdoor scenes.
Extrapolating Large-Scale Material BTFs under Cross-Device Constraints
(The Eurographics Association, 2015) Steinhausen, Heinz Christian; Brok, Dennis den; Hullin, Matthias B.; Klein, Reinhard; David Bommes and Tobias Ritschel and Thomas Schultz
In this paper, we address the problem of acquiring bidirectional texture functions (BTFs) of large-scale material samples. Our approach fuses gonioreflectometric measurements of small samples with few constraint images taken on a flatbed scanner under semi-controlled conditions. Underlying our method is a lightweight texture synthesis scheme using a local texture descriptor that combines shading and albedo across devices. Since it operates directly on SVD-compressed BTF data, our method is computationally efficient and can be implemented on a moderate memory footprint.
Fast Accurate Soft Shadows with Adaptive Light Source Sampling
(The Eurographics Association, 2012) Schwärzler, Michael; Mattausch, Oliver; Scherzer, Daniel; Wimmer, Michael; Michael Goesele and Thorsten Grosch and Holger Theisel and Klaus Toennies and Bernhard Preim
Physically accurate soft shadows in 3D applications can be simulated by taking multiple samples from all over the area light source and accumulating them. Due to the unpredictability of the size of the penumbra regions, the required sampling density has to be high in order to guarantee smooth shadow transitions in all cases. Hence, several hundreds of shadow maps have to be evaluated in any scene configuration, making the process computationally expensive. Thus, we suggest an adaptive light source subdivision approach to select the sampling points adaptively. The main idea is to start with a few samples on the area light, evaluating there differences using hardware occlusion queries, and adding more sampling points if necessary. Our method is capable of selecting and rendering only the samples which contribute to an improved shadow quality, and hence generate shadows of comparable quality and accuracy. Even though additional calculation time is needed for the comparison step, this method saves valuable rendering time and achieves interactive to real-time frame rates in many cases where a brute force sampling method does not.
GPU-accelerated Interactive Material Aging
(The Eurographics Association, 2012) Günther, Tobias; Rohmer, Kai; Grosch, Thorsten; Michael Goesele and Thorsten Grosch and Holger Theisel and Klaus Toennies and Bernhard Preim
A photorealistic appearance of a 3D scene is required in many applications today. Thereby, one vital aspect is the usage of realistic materials, for which a broad variety of reflectance models is available. When directly employing those models, surfaces always look new, which contrasts strongly the real objects surrounding us as they have undergone diverse kinds of aging processes. The literature already proposes a set of viable methods to simulate different aging phenomena, but all of them are computationally expensive and can thus only be computed off-line. Therefore, this paper presents the first interactive, GPU-accelerated method to simulate material aging in a given scene. Thereby, our approach allows artists to precisely control the course of the aging process. Our particlebased method is capable to reproduce the most common deterioration phenomena in a few seconds, including plausible dirt bleeding, flow effects, corrosion and patina.
Interactive Appearance Editing in RGB-D Images
(The Eurographics Association, 2014) Bergmann, Stephan; Ritschel, Tobias; Dachsbacher, Carsten; Jan Bender and Arjan Kuijper and Tatiana von Landesberger and Holger Theisel and Philipp Urban
The availability of increasingly powerful and affordable image and depth sensors in conjunction with the necessary processing power creates novel possibilities for more sophisticated and powerful image editing tools. Along these lines we present a method to alter the appearance of objects in RGB-D images by re-shading their surfaces with arbitrary BRDF models and subsurface scattering using the dipole diffusion approximation. To evaluate the incident light for re-shading we combine ray marching using the depth buffer as approximate geometry and environment lighting. The environment map is built from information solely contained in the RGB-D input image exploiting both the reflections on glossy surfaces as well as geometric information. Our CPU/GPU implementation provides interactive feedback to facilitate intuitive editing.We compare and demonstrate our method with rendered images and digital photographs.
An Interactive Appearance Model for Microscopic Fiber Surfaces
(The Eurographics Association, 2016) Velinov, Zdravko; Hullin, Matthias B.; Matthias Hullin and Marc Stamminger and Tino Weinkauf
Modeling and rendering the appearance of fabrics remains one of the most challenging research topics in computer graphics. Today's most advanced models are based on volumetric fiber distributions, obtained from advanced measurement techniques like micro-CT, and only renderable through expensive volume rendering approaches. In this paper, we propose an analytical BRDF model for pile fabrics, i.e., textiles like velvet, plush or Alcantara, that are characterized by open-ended strands of yarn. A fascinating property of many such materials is that they ''memorize'' tactile interaction and that their appearance depends on the last direction in which the surface was brushed. Our reflectance model, inspired by recent microflake models, links the microscopic structure of a material to the interaction that caused that structure, and to the resulting macroscopic reflectance behavior. We present an end-to-end pipeline for fitting the parameters of our model to measured reflectance data, for manipulating fiber distributions using tactile input, and rendering the resulting spatially varying surface appearance in real time.
Screen Space Spherical Harmonic Occlusion
(The Eurographics Association, 2012) Herholz, Sebastian; Schairer, Timo; Schilling, Andreas; Straßer, Wolfgang; Michael Goesele and Thorsten Grosch and Holger Theisel and Klaus Toennies and Bernhard Preim
In this paper we present a new algorithm for real-time directional occlusion sampling. We combine the real-time capabilities of Screen Space Ambient Occlusion (SSAO) with the Spherical Harmonics (SH) representation of local directional occlusion. SH are well established and used in modern off-line rendering implementations such as PantaRay [PFHA10]. Through our combination we are able to transfer a method for realistic local directional occlusion effects from offline rendering to dynamic real-time applications. These local occlusion effects react to the environmental lighting situation and lead to dynamic and colored local occlusion shadows while only generating a small computational overhead compared to SSAO. Unlike other real-time directional occlusion algorithms such as Screen Space Direction Occlusion (SSDO) [RGS09] our occlusion sampling is separated from the actual lighting process and therefore can be easily integrated in existing SH lighting methods such as Irradiance Volumes [GSHG98]. We furthermore extend our algorithm to include first bounce indirect illumination effects.
Supporting Urban Search & Rescue Mission Planning through Visualization-Based Analysis
(The Eurographics Association, 2014) Bock, Alexander; Kleiner, Alexander; Lundberg, Jonas; Ropinski, Timo; Jan Bender and Arjan Kuijper and Tatiana von Landesberger and Holger Theisel and Philipp Urban
We propose a visualization system for incident commanders in urban search & rescue scenarios that supports access path planning for post-disaster structures. Utilizing point cloud data acquired from unmanned robots, we provide methods for assessment of automatically generated paths. As data uncertainty and a priori unknown information make fully automated systems impractical, we present a set of viable access paths, based on varying risk factors, in a 3D environment combined with the visual analysis tools enabling informed decisions and trade-offs. Based on these decisions, a responder is guided along the path by the incident commander, who can interactively annotate and reevaluate the acquired point cloud to react to the dynamics of the situation. We describe design considerations for our system, technical realizations, and discuss the results of an expert evaluation.
Visualization of Cardiac Blood Flow Using Anisotropic Ambient Occlusion for Lines
(The Eurographics Association, 2017) Köhler, Benjamin; Grothoff, Matthias; Gutberlet, Matthias; Preim, Bernhard; Matthias Hullin and Reinhard Klein and Thomas Schultz and Angela Yao
Ambient occlusion (AO) for lines (LineAO) was introduced by Eichelbaum et al. [EHS13] as an adaption of screen-space AO to static line bundles, such as white brain matter fiber tracts derived from diffusion tensor imaging (DTI). In this paper, we further adapt the LineAO technique to dynamic scenes, in particular the animation of blood flow-representing pathlines that were integrated in cardiac 4D phase-contrast magnetic resonance imaging (PC-MRI) data. 4D PC-MRI is a non-invasive technique that allows to acquire time-resolved blood flow velocity data in all three spatial dimensions, i.e., a 4D vector field of one heart beat. Our main extension is a line alignment factor that reduces the AO-induced darkening if nearby lines have similar screen-space tangents. We further enhance the perception of homogeneous flow by incorporating depth-dependent halos. Our technique facilitates the quicker identification of prominent flow structures while showing the full flow context.

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