26-Issue 3

Permanent URI for this collection

https://diglib.eg.org/handle/10.2312/131

Browse

Now showing 1 - 20 of 53

Style Transfer Functions for Illustrative Volume Rendering
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Bruckner, S.; Groeller, M. E.
Illustrative volume visualization frequently employs non-photorealistic rendering techniques to enhance important features or to suppress unwanted details. However, it is difficult to integrate multiple non-photorealistic rendering approaches into a single framework due to great differences in the individual methods and their parameters. In this paper, we present the concept of style transfer functions. Our approach enables flexible data-driven illumination which goes beyond using the transfer function to just assign colors and opacities. An image-based lighting model uses sphere maps to represent non-photorealistic rendering styles. Style transfer functions allow us to combine a multitude of different shading styles in a single rendering. We extend this concept with a technique for curvature-controlled style contours and an illustrative transparency model. Our implementation of the presented methods allows interactive generation of high-quality volumetric illustrations.
Global Illumination using Photon Ray Splatting
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Herzog, Robert; Havran, Vlastimil; Kinuwaki, Shinichi; Myszkowski, Karol; Seidel, Hans-Peter
We present a novel framework for efficiently computing the indirect illumination in diffuse and moderately glossy scenes using density estimation techniques. Many existing global illumination approaches either quickly compute an overly approximate solution or perform an orders of magnitude slower computation to obtain high-quality results for the indirect illumination. The proposed method improves photon density estimation and leads to significantly better visual quality in particular for complex geometry, while only slightly increasing the computation time. We perform direct splatting of photon rays, which allows us to use simpler search data structures. Since our density estimation is carried out in ray space rather than on surfaces, as in the commonly used photon mapping algorithm, the results are more robust against geometrically incurred sources of bias. This holds also in combination with final gathering where photon mapping often overestimates the illumination near concave geometric features. In addition, we show that our photon splatting technique can be extended to handle moderately glossy surfaces and can be combined with traditional irradiance caching for sparse sampling and filtering in image space.
A Bidirectional Light Field - Hologram Transform
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Ziegler, Remo; Bucheli, Simon; Ahrenberg, Lukas; Magnor, Marcus; Gross, Markus
In this paper, we propose a novel framework to represent visual information. Extending the notion of conventional image-based rendering, our framework makes joint use of both light fields and holograms as complementary representations. We demonstrate how light fields can be transformed into holograms, and vice versa. By exploiting the advantages of either representation, our proposed dual representation and processing pipeline is able to overcome the limitations inherent to light fields and holograms alone. We show various examples from synthetic and real light fields to digital holograms demonstrating advantages of either representation, such as speckle-free images, ghosting-free images, aliasing-free recording, natural light recording, aperture-dependent effects and real-time rendering which can all be achieved using the same framework. Capturing holograms under white light illumination is one promising application for future work.
A Generic Pigment Model for Digital Painting
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Xu, Songhua; Tan, Haisheng; Jiao, Xiantao; Lau, Francis C.M.; Pan, Yunhe
Consistent Viewing and Interaction for Multiple Users in Projection-Based VR Systems
(The Eurographics Association and Blackwell Publishing Ltd, 2007) De Haan, Gerwin; Molenaar, Rene; Koutek, Michal; Post, Frits H.
In projection-based Virtual Reality (VR) systems, typically only one headtracked user views stereo images rendered from the correct view position. For other users, who are presented a distorted image, moving with the first user s head motion, it is difficult to correctly view and interact with 3D objects in the virtual environment. In close-range VR systems, such as the Virtual Workbench, distortion effects are especially large because objects are within close range and users are relatively far apart. On these systems, multi-user collaboration proves to be difficult. In this paper, we analyze the problem and describe a novel, easy to implement method to prevent and reduce image distortion and its negative effects on close-range interaction task performance. First, our method combines a shared camera model and view distortion compensation. It minimizes the overall distortion for each user, while important user-personal objects such as interaction cursors, rays and controls remain distortion-free. Second, our method retains co-location for interaction techniques to make interaction more consistent. We performed a user experiment on our Virtual Workbench to analyze user performance under distorted view conditions with and without the use of our method. Our findings demonstrate the negative impact of view distortion on task performance and the positive effect our method introduces. This indicates that our method can enhance the multi-user collaboration experience on close-range, projection-based VR systems.
Volume Preservation of Multiresolution Meshes
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Sauvage, Basile; Hahmann, Stefanie; Bonneau, Georges-Pierre
Geometric constraints have proved to be efficient for enhancing the realism of shape animation. The present paper addresses the computation and the preservation of the volume enclosed by multiresolution meshes. A wavelet based representation allows the mesh to be handled at any level of resolution. The key contribution is the calculation of the volume as a trilinear form with respect to the multiresolution coefficients. Efficiency is reached thanks to the pre-processing of a sparse 3D data structure involving the transposition of the filters while represented as a lifting scheme. A versatile and interactive method for preserving the volume during a deformation process is then proposed. It is based on a quadratic minimization subject to a linearization of the volume constraint. A closed form of the solution is derived.
Interactive Simulation of the Human Eye Depth of Field and Its Correction by Spectacle Lenses
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Kakimoto, Masanori; Tatsukawa, Tomoaki; Mukai, Yukiteru; Nishita, Tomoyuki
This paper describes a fast rendering algorithm for verification of spectacle lens design. Our method simulates refraction corrections of astigmatism as well as myopia or presbyopia. Refraction and defocus are the main issues in the simulation. For refraction, our proposed method uses per-vertex basis ray tracing which warps the environment map and produces a real-time refracted image which is subjectively as good as ray tracing. Conventional defocus simulation was previously done by distribution ray tracing and a real-time solution was impossible. We introduce the concept of a blur field, which we use to displace every vertex according to its position. The blurring information is precomputed as a set of field values distributed to voxels which are formed by evenly subdividing the perspective projected space. The field values can be determined by tracing a wavefront from each voxel through the lens and the eye, and by evaluating the spread of light at the retina considering the best human accommodation effort. The blur field is stored as texture data and referred to by the vertex shader that displaces each vertex. With an interactive frame rate, blending the multiple rendering results produces a blurred image comparable to distribution ray tracing output.
Crowds by Example
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Lerner, Alon; Chrysanthou, Yiorgos; Lischinski, Dani
We present an example-based crowd simulation technique. Most crowd simulation techniques assume that the behavior exhibited by each person in the crowd can be defined by a restricted set of rules. This assumption limits the behavioral complexity of the simulated agents. By learning from real-world examples, our autonomous agents display complex natural behaviors that are often missing in crowd simulations. Examples are created from tracked video segments of real pedestrian crowds. During a simulation, autonomous agents search for examples that closely match the situation that they are facing. Trajectories taken by real people in similar situations, are copied to the simulated agents, resulting in seemingly natural behaviors.
Precomputed Radiance Transfer Field for Rendering Interreflections in Dynamic Scenes
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Pan, Minghao; Wang Xinguo Liu, Rui; Peng, Qunsheng; Bao, Hujun
In this paper, we introduce a new representation - radiance transfer fields (RTF) - for rendering interreflections in dynamic scenes under low frequency illumination. The RTF describes the radiance transferred by an individual object to its surrounding space as a function of the incident radiance. An important property of RTF is its independence of the scene configuration, enabling interreflection computation in dynamic scenes. Secondly, RTFs naturally fit in with the rendering framework of precomputed shadow fields, incurring negligible cost to add interreflection effects. In addition, RTFs can be used to compute interreflections for both diffuse and glossy objects. We also show that RTF data can be highly compressed by clustered principal component analysis (CPCA), which not only reduces the memory cost but also accelerates rendering. Finally, we present some experimental results demonstrating our techniques.
Omni-directional Relief Impostors
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Andujar, C.; Boo, J.; Brunet, P.; Fairen, M.; Navazo, I.; Vazquez, P.; Vinacua, A.
Relief impostors have been proposed as a compact and high-quality representation for high-frequency detail in 3D models. In this paper we propose an algorithm to represent a complex object through the combination of a reduced set of relief maps. These relief maps can be rendered with very few artifacts and no apparent deformation from any view direction. We present an efficient algorithm to optimize the set of viewing planes supporting the relief maps, and an image-space metric to select a sufficient subset of relief maps for each view direction. Selected maps (typically three) are rendered based on the well-known ray-height-field intersection algorithm implemented on the GPU. We discuss several strategies to merge overlapping relief maps while minimizing sampling artifacts and to reduce extra texture requirements. We show that our representation can maintain the geometry and the silhouette of a large class of complex shapes with no limit in the viewing direction. Since the rendering cost is output sensitive, our representation can be used to build a hierarchical model of a 3D scene.
Shape-aware Volume Illustration
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Chen, Wei; Lu, Aidong; Ebert, David S.
We introduce a novel volume illustration technique for regularly sampled volume datasets. The fundamental difference between previous volume illustration algorithms and ours is that our results are shape-aware, as they depend not only on the rendering styles, but also the shape styles. We propose a new data structure that is derived from the input volume and consists of a distance volume and a segmentation volume. The distance volume is used to reconstruct a continuous field around the object boundary, facilitating smooth illustrations of boundaries and silhouettes. The segmentation volume allows us to abstract or remove distracting details and noise, and apply different rendering styles to different objects and components. We also demonstrate how to modify the shape of illustrated objects using a new 2D curve analogy technique. This provides an interactive method for learning shape variations from 2D hand-painted illustrations by drawing several lines. Our experiments on several volume datasets demonstrate that the proposed approach can achieve visually appealing and shape-aware illustrations. The feedback from medical illustrators is quite encouraging.
Texturing Internal Surfaces from a Few Cross Sections
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Pietroni, Nico; Otaduy, Miguel A.; Bickel, Bernd; Ganovelli, Fabio; Gross, Markus
We introduce a new appearance-modeling paradigm for synthesizing the internal structure of a 3D model from photographs of a few cross-sections of a real object. When the internal surfaces of the 3D model are revealed as it is cut, carved, or simply clipped, we synthesize their texture from the input photographs. Our texture synthesis algorithm is best classified as a morphing technique, which efficiently outputs the texture attributes of each surface point on demand. For determining source points and their weights in the morphing algorithm, we propose an interpolation domain based on BSP trees that naturally resembles planar splitting of real objects. In the context of the interpolation domain, we define efficient warping and morphing operations that allow for real-time synthesis of textures. Overall, our modeling paradigm, together with its realization through our texture morphing algorithm, allow users to author 3D models that reveal highly realistic internal surfaces in a variety of artistic flavors.
What can Computer Graphics expect from 3D Computer Vision?
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Sara, Radim
Computer Vision is a discipline whose ultimate goal is to interpret optical images of real scenes. It is well understood that such a problem is cursed by ambiguity of interpretation and uncertainty of evidence. Despite imperfectness of results due to the scenes never following our prior models exactly, Computer Vision has achieved a significant progress in the past two decades.This talk will outline the quest of 3D Computer Vision by describing a processing pipeline that receives a heap of unorganized images from unknown cameras and produces a consistent 3D geometric model together with camera calibrations. We will see how new algorithms allow the standard conception of the pipeline as a series of independent processing steps gradually transform to a single complex, yet efficient vision task. We will identify some points where linking Computer Vision and Computer Graphics would bring significant progress.
On-the-fly Curve-skeleton Computation for 3D Shapes
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Sharf, Andrei; Lewiner, Thomas; Shamir, Ariel; Kobbelt, Leif
The curve-skeleton of a 3D object is an abstract geometrical and topological representation of its 3D shape. It maps the spatial relation of geometrically meaningful parts to a graph structure. Each arc of this graph represents a part of the object with roughly constant diameter or thickness, and approximates its centerline. This makes the curve-skeleton suitable to describe and handle articulated objects such as characters for animation. We present an algorithm to extract such a skeleton on-the-fly, both from point clouds and polygonal meshes. The algorithm is based on a deformable model evolution that captures the object s volumetric shape. The deformable model involves multiple competing fronts which evolve inside the object in a coarse-to-fine manner. We first track these fronts centers, and then merge and filter the resulting arcs to obtain a curve-skeleton of the object. The process inherits the robustness of the reconstruction technique, being able to cope with noisy input, intricate geometry and complex topology. It creates a natural segmentation of the object and computes a center curve for each segment while maintaining a full correspondence between the skeleton and the boundary of the object.
Contrast Restoration by Adaptive Countershading
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Krawczyk, Grzegorz; Myszkowski, Karol; Seidel, Hans-Peter
The ABSTRACT is to be in fully-justified italicized text, between two horizontal lines, in one-column format, below the author and affiliation information. Use the word Abstract as the title, in 9-point Times, boldface type, left-aligned to the text, initially capitalized. The abstract is to be in 9-point, single-spaced type. The abstract may be up to 3 inches (7.62 cm) long. Leave one blank line after the abstract, then add the subject categories according to the ACM Classification Index (see http://www.acm.org/class/1998/).
Efficient Reflectance and Visibility Approximations for Environment Map Rendering
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Green, Paul; Kautz, Jan; Durand, Fredo
We present a technique for approximating isotropic BRDFs and precomputed self-occlusion that enables accurate and efficient prefiltered environment map rendering. Our approach uses a nonlinear approximation of the BRDF as a weighted sum of isotropic Gaussian functions. Our representation requires a minimal amount of storage, can accurately represent BRDFs of arbitrary sharpness, and is above all, efficient to render. We precompute visibility due to self-occlusion and store a low-frequency approximation suitable for glossy reflections. We demonstrate our method by fitting our representation to measured BRDF data, yielding high visual quality at real-time frame rates.
Skeleton-based Variational Mesh Deformations
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Yoshizawa, Shin; Belyaev, Alexander; Seidel, Hans-Peter
In this paper, a new free-form shape deformation approach is proposed. We combine a skeleton-based mesh deformation technique with discrete differential coordinates in order to create natural-looking global shape deformations. Given a triangle mesh, we first extract a skeletal mesh, a two-sided Voronoibased approximation of the medial axis. Next the skeletal mesh is modified by free-form deformations. Then a desired global shape deformation is obtained by reconstructing the shape corresponding to the deformed skeletal mesh. The reconstruction is based on using discrete differential coordinates. Our method preserves fine geometric details and original shape thickness because of using discrete differential coordinates and skeleton-based deformations. We also develop a new mesh evolution technique which allow us to eliminate possible global and local self-intersections of the deformed mesh while preserving fine geometric details. Finally, we present a multi-resolution version of our approach in order to simplify and accelerate the deformation process. In addition, interesting links between the proposed free-form shape deformation technique and classical and modern results in the differential geometry of sphere congruences are established and discussed.
Ray-Casted BlockMaps for Large Urban Models Visualization
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Cignoni, P.; Di Benedetto, M.; Ganovelli, F.; Gobbetti, E.; Marton, F.; Scopigno, R.
We introduce a GPU-friendly technique that efficiently exploits the highly structured nature of urban environments to ensure rendering quality and interactive performance of city exploration tasks. Central to our approach is a novel discrete representation, called BlockMap, for the efficient encoding and rendering of a small set of textured buildings far from the viewer. A BlockMap compactly represents a set of textured vertical prisms with a bounded on-screen footprint. BlockMaps are stored into small fixed size texture chunks and efficiently rendered through GPU raycasting. Blockmaps can be seamlessly integrated into hierarchical data structures for interactive rendering of large textured urban models. We illustrate an efficient output-sensitive framework in which a visibility-aware traversal of the hierarchy renders components close to the viewer with textured polygons and employs BlockMaps for far away geometry. Our approach provides a bounded size far distance representation of cities, naturally scales with the improving shader technology, and outperforms current state of the art approaches. Its efficiency and generality is demonstrated with the interactive exploration of a large textured model of the city of Paris on a commodity graphics platform.
Online Motion Capture Marker Labeling for Multiple Interacting Articulated Targets
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Yu, Qian; Li, Qing; Deng, Zhigang
In this paper, we propose an online motion capture marker labeling approach for multiple interacting articulated targets. Given hundreds of unlabeled motion capture markers from multiple articulated targets that are interacting each other, our approach automatically labels these markers frame by frame, by fitting rigid bodies and exploiting trained structure and motion models. Advantages of our approach include: 1) our method is an online algorithm, which requires no user interaction once the algorithm starts. 2) Our method is more robust than traditional the closest point-based approaches by automatically imposing the structure and motion models. 3) Due to the use of the structure model which encodes the rigidity of each articulated body of captured targets, our method can recover missing markers robustly. Our approach is efficient and particularly suited for online computer animation and video game applications.
Soft Articulated Characters with Fast Contact Handling
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Galoppo, Nico; Otaduy, Miguel A.; Tekin, Serhat; Gross, Markus; Lin, Ming C.
Fast contact handling of soft articulated characters is a computationally challenging problem, in part due to complex interplay between skeletal and surface deformation. We present a fast, novel algorithm based on a layered representation for articulated bodies that enables physically-plausible simulation of animated characters with a high-resolution deformable skin in real time. Our algorithm gracefully captures the dynamic skeleton-skin interplay through a novel formulation of elastic deformation in the pose space of the skinned surface. The algorithm also overcomes the computational challenges by robustly decoupling skeleton and skin computations using careful approximations of Schur complements, and efficiently performing collision queries by exploiting the layered representation. With this approach, we can simultaneously handle large contact areas, produce rich surface deformations, and capture the collision response of a character/s skeleton.

Browse

Browsing 26-Issue 3 by Issue Date

Results Per Page

Sort Options