VG07: Eurographics/IEEE VGTC Symposium on Volume Graphics 2007
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Item 3D Reconstruction of Emission and Absorption in Planetary Nebulae(The Eurographics Association, 2007) Lintu, Andrei; Lensch, Hendrik P. A.; Magnor, Marcus; El-Abed, Sascha; Seidel, Hans-Peter; H.-C. Hege and R. Machiraju and T. Moeller and M. SramekThis paper addresses the problem of reconstructing the 3D structure of planetary nebulae from 2D observations. Assuming axial symmetry, our method jointly reconstructs the distribution of dust and ionized gas in the nebulae from observations at two different wavelengths. In an inverse rendering framework we optimize for the emission and absorption densities which are correlated to the gas and dust distribution present in the nebulae. First, the density distribution of the dust component is estimated based on an infrared image, which traces only the dust distribution due to its intrinsic temperature. In a second step, we optimize for the gas distribution by comparing the rendering of the nebula to the visible wavelength image. During this step, besides the emission of the ionized gas, we further include the effect of absorption and scattering due to the already estimated dust distribution. Using the same approach, we can as well start with a radio image from which the gas distribution is derived without absorption, then deriving the dust distribution from the visible wavelength image considering absorption and scattering. The intermediate steps and the final reconstruction results are visualized at real-time frame rates using a volume renderer. Using our method we recover both gas and dust density distributions present in the nebula by exploiting the distinct absorption or emission parameters at different wavelengths.Item Accelerated Light Propagation Through Participating Media(The Eurographics Association, 2007) Lee, Richard; O'Sullivan, Carol; H.-C. Hege and R. Machiraju and T. Moeller and M. SramekMonte Carlo path tracing is a simple and effective way to solve the volume rendering equation. However, propagating light paths through participating media can be very costly because of the need to simulate potentially many scattering events. This paper presents a simple technique to accelerate path tracing of homogeneous participating media. We use a traditional path tracer for scattering near the surface but switch to a new approach for handling paths that penetrate far enough inside the medium. These paths are determined by sampling from a set of precomputed probability distributions, which avoids the need to simulate individual scattering events or perform ray intersection tests with the environment. We demonstrate cases where our approach leads to accurate and more efficient rendering of participating media, including subsurface scattering in translucent materials.Item Applications of Optimal Sampling Lattices for Volume Acquisition via 3D Computed Tomography(The Eurographics Association, 2007) Xu, Fang; Mueller, Klaus; H.-C. Hege and R. Machiraju and T. Moeller and M. SramekThere has been mounting evidence that the familiar Cartesian lattices, while convenient for signal processing and representation, are sub-optimal when it comes to signal fidelity. More suitable in this respect are optimal sampling lattices, such as the Hexagonal and Body Centered Cartesian (BCC) lattice, and recent work has employed these in the areas of volume rendering and image processing. In this paper we explore various applications of these lattices within the context of 3D Computed Tomographic Reconstruction, both in terms of the (2D) detector and the (3D) reconstructed object, and a theoretical analysis is provided. We combine this analysis with a practical application, that is, the use of these lattices within a real-time GPU-accelerated 3D reconstruction platform, in which performance is also of an immediate concern.Item Automatic Feature Modeling Techniques for Volume Segmentation Applications(The Eurographics Association, 2007) Huang, Runzhen; Yu, Hongfeng; Ma, Kwan-Liu; Staadt, Oliver; H.-C. Hege and R. Machiraju and T. Moeller and M. SramekIn many volume segmentation and visualization tasks, the ability to correctly identify the boundary surface of each volumetric feature of interest in the data is desirable. This surface can be used in subsequent quantitative studies of the segmented features. In this paper, we present an automatic approach to generate accurate representations of a feature of interest from volume segmentation. Our method first locates a set of points, which tightly define the boundary of the volumetric feature. This set of points can then be used to construct a boundary surface mesh. We also describe how to construct an anti-aliased volume representation of the segmented feature from this point set to enable high-quality volume rendering of the feature. These three representations - point set, boundary surface mesh, and anti-aliased volume segment - have a wide variety of applications.Item Efficient Ambient and Emissive Tissue Illumination using Local Occlusion in Multiresolution Volume Rendering(The Eurographics Association, 2007) Hernell, Frida; Ljung, Patric; Ynnerman, Anders; H.-C. Hege and R. Machiraju and T. Moeller and M. SramekThis paper introduces a novel technique to compute illumination for Direct Volume Rendering. By adding shadow effects to volume rendered images, the perception of shapes and tissue properties can be significantly improved and it has the potential to increase the diagnostic value of medical volume rendering. The integrated intensity of incident light for a voxel is computed using a local approximation of the ambient occlusion, thus avoiding the rendering of tissues with very low illumination. Luminous tissue effects are also introduced to enhance the illumination model, controlled through an emissive component in the transfer function. This effect allows the user to highlight specific structures and can give a better understanding of tissue density. Multiresolution volume management and GPU-based computation is used to significantly speed-up the calculations and to support large data sets. The scheme yields interactive frame rates for incrementally refined ambient and emissive illumination for arbitrary transfer function changes.Item Feature Enhancement using Locally Adaptive Volume Rendering(The Eurographics Association, 2007) Marchesin, Stephane; Dischler, Jean-Michel; Mongenet, Catherine; H.-C. Hege and R. Machiraju and T. Moeller and M. SramekClassical direct volume rendering techniques accumulate color and opacity contributions using the standard volume rendering equation approximated by alpha blending. However, such standard rendering techniques, often also aiming at visual realism, are not always adequate for efficient data exploration, especially when large opaque areas are present in a dataset, since such areas can occlude important features and make them invisible. On the other hand, the use of highly transparent transfer functions allows viewing all the features at once, but often makes these features barely visible. In this paper we introduce a new, straightforward rendering technique called locally adaptive volume rendering, that consists in slightly modifying the traditional volume rendering equation in order to improve the visibility of the features, independently of any transfer function. Our approach is fully automatic and based only on an initial binary classification of empty areas. This classification is used to dynamically adjust the opacity of the contributions per-pixel depending on the number of non-empty contributions to that pixel. As will be shown by our comparative study with standard volume rendering, this makes our rendering method much more suitable for interactive data exploration at a low extra cost. Thereby, our method avoids feature visibility restrictions without relying on a transfer function and yet maintains a visual similarity with standard volume rendering.Item (No) More Marching Cubes(The Eurographics Association, 2007) Carr, Hamish; H.-C. Hege and R. Machiraju and T. Moeller and M. SramekIsosurfaces, one of the most fundamental volumetric visualization tools, are commonly rendered using the wellknown Marching Cubes cases that approximate contours of trilinearly-interpolated scalar fields. While a complete set of cases has recently been published by Nielson, the formal proof that these cases are the only ones possible and that they are topologically correct is difficult to follow. We present a more straightforward proof of the correctness and completeness of these cases based on a variation of the Dividing Cubes algorithm. Since this proof is based on topological arguments and a divide-and-conquer approach, this also sets the stage for developing tessellation cases for higher-order interpolants and for the quadrilinear interpolant in four dimensions. We also demonstrate that, apart from degenerate cases, Nielson's cases are in fact subsets of two basic configurations of the trilinear interpolant.Item Palette-Style Volume Visualization(The Eurographics Association, 2007) Wu, Yingcai; Xu, Anbang; Chan, Ming-Yuen; Qu, Huamin; Guo, Ping; H.-C. Hege and R. Machiraju and T. Moeller and M. SramekIn this paper we propose a palette-style volume visualization interface which aims at providing users with an intuitive volume exploration tool. Our system is inspired by the widely used wheel-style color palette. The system initially creates a set of direct volume rendered images (DVRIs) manually or automatically, and arranges them over a circle in 2D image space. Based on the initial set of DVRIs called primary DVRIs which imitate the primary colors in the color wheel, users can create more DVRIs on the wheel using PhotoShop-style image editing operations such as the fusing operation. With our system, non-expert users can easily navigate and explore volumetric data. In addition, users can always know where they have been, where they are, and where they could go in a visualization process and hence redundant exploration can be avoided.Item Quality Enhancement of Direct Volume Rendered Images(The Eurographics Association, 2007) Chan, Ming-Yuen; Wu, Yingcai; Qu, Huamin; H.-C. Hege and R. Machiraju and T. Moeller and M. SramekIn this paper, we propose a new method for enhancing the quality of direct volume rendered images. Unlike the typical image enhancement techniques which perform transformations in the image domain, we take the volume data into account and enhance the presentation of the volume in the rendered image by adjusting the rendering parameters. Our objective is not only to deliver a pleasing image with better color contrast or enhanced features, but also generate a faithful image with the information in the volume presented in the image. An image quality measurement is proposed to quantitatively evaluate image quality based on the information obtained from the image as well as the volumetric data. The parameter adjustment process is driven by the evaluation result using a genetic algorithm. More informative and comprehensible results are therefore delivered, compared with the typical image-based approaches.Item Simultaneous GPU-Assisted Raycasting of Unstructured Point Sets and Volumetric Grid Data(The Eurographics Association, 2007) Kaehler, Ralf; Abel, Tom; Hege, Hans-Christian; H.-C. Hege and R. Machiraju and T. Moeller and M. SramekIn the recent years the advent of powerful graphics hardware with programmable pixel shaders enabled interactive raycasting implementations on low-cost commodity desktop computers. Unlike slice-based volume rendering approaches GPU-assisted raycasting does not suffer from rendering artifacts caused by varying sample distances along different ray-directions or limited frame-buffer precision. It further supports direct implementations of many sophisticated acceleration techniques and lighting models. In this paper we present a GPU-assisted raycasting approach for data that consists of volumetric fields defined on computational grids as well as unstructured point sets. We avoid resampling the point data onto proxy grids by directly encoding the point data in a GPU-octree data structure. This allows to efficiently access the (semitransparent) point data during ray traversal and correctly blend it with the grid data, yielding interactive, highquality rendering results. We discuss approaches to accelerate the rendering performance for larger point sets and give real world application examples to demonstrate the usefulness of our approach.Item Surface Reconstruction from Noisy Point Clouds using Coulomb Potentials(The Eurographics Association, 2007) Jalba, A.C.; Roerdink, J.B. T.M.; H.-C. Hege and R. Machiraju and T. Moeller and M. SramekWe show that surface reconstruction from point clouds without orientation information can be formulated as a convection problem in a force field based on Coulomb potentials. To efficiently evaluate Coulomb potentials on the volumetric grid on which the evolving surface (current approximation to the final surface) is convected we use the so called 'Particle-Particle Particle-Mesh' (PPPM) algorithm from molecular dynamics, fully implemented on modern, programmable graphics hardware. Our approach offers a number of advantages. Unlike distance-based methods which are sensitive to noise, the proposed method is highly resilient to shot noise since global Coulomb potentials are used to disregard outliers due to noise. Unlike local fitting, the long-range nature of Coulomb potentials implies that all data points are considered at once, so that global information is used in the fitting process. The method compares favorably with respect to previous approaches in terms of speed and flexibility and is highly resilient to noiseItem Variational Volumetric Surface Reconstruction from Unorganized Points(The Eurographics Association, 2007) Jakobsen, Bjarke; Bærentzen, J. Andreas; Christensen, Niels Jørgen; H.-C. Hege and R. Machiraju and T. Moeller and M. SramekReconstruction of smooth surfaces from point sets is an important problem in many applications since this sort of data often appear in real-life scenarios. This paper presents method for solving this this problem at interactive rates by means of second order energy minimization obtained by solving Delta <sup>2</sup>Item Volume Deformation via Scattered Data Interpolation(The Eurographics Association, 2007) Correa, Carlos D.; Silver, Deborah; Chen, Min; H.-C. Hege and R. Machiraju and T. Moeller and M. SramekWith the advent of contemporary GPUs, it has been possible to perform volume deformation at interactive rates. In particular, it has been shown that deformation can be important for the purposes of illustration. In such cases, rather than being the result of a physically-based simulation, volume deformation is often goal-oriented and user-guided. For this purpose, it is important to provide the user with tools for directly specifying a deformation interactively and refine it based on constraints or user intention. In many cases, deformation is obtained based on a reference object or image. In this paper, we present a method for deforming volumetric objects based on user guided scattered data interpolation. A GPU-based implementation enables real-time manipulation of 2D images and volumes. We show how this approach can have applications in scientific illustration, volume exploration and visualization, generation of animations and special effects, among others.