In this paper, we present a novel technique which simulates directional light scattering for more realistic interactive visualization of volume data. Our method extends the recent directional occlusion shading model by enabling light source positioning with practically no performance penalty. Light transport is approximated using a tilted cone-shaped function which leaves elliptic footprints in the opacity buffer during slice-based volume rendering. We perform an incremental blurring operation on the opacity buffer for each slice in front-to-back order. This buffer is then used to define the degree of occlusion for the subsequent slice. Our method is capable of generating high-quality soft shadowing effects, allows interactive modification of all illumination and rendering parameters, and requires no pre-computation. Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism —Color, shading, shadowing, and texture 1.

In this paper, we introduce the concept of isosurface similarity maps for the visualization of volume data. Isosurface similarity maps present structural information of a volume data set by depicting similarities between individual isosurfaces quantified by a robust information-theoretic measure. Unlike conventional histograms, they are not based on the frequency of isovalues and/or derivatives and therefore provide complementary information. We demonstrate that this new representation can be used to guide transfer function design and visualization parameter specification. Furthermore, we use isosurface similarity to develop an automatic parameter-free method for identifying representative isovalues. Using real-world data sets, we show that isosurface similarity maps can be a useful addition to conventional classification techniques. Categories and Subject Descriptors (according to ACM CCS): Generation—Display algorithms I.3.3 [Computer Graphics]: Picture/Image 1.

Seismic horizons indicate change in rock properties and are central in geoscience interpretation. Traditional interpretation systems involve time consuming and repetitive manual volumetric seeding for horizon growing. We present a novel system for rapidly interpreting and visualizing seismic volumetric data. First we extract horizon surface-parts by preprocessing the seismic data. Then during interaction the user can assemble in realtime the horizon parts into horizons. Traditional interpretation systems use gradient-based illumination models in the rendering of the seismic volume and polygon rendering of horizon surfaces. We employ realtime gradientfree forward-scattering in the rendering of seismic volumes yielding results similar to high-quality global illumination. We use an implicit surface representation of horizons allowing for a seamless integration of horizon rendering and volume rendering. We present a collection of novel techniques constituting an interpretation and visualization system highly tailored to seismic data interpretation.

Fig. 1. Volume renderings of a numerical flow simulation data set. (a) Volumetric ambient occlusion and specular highlights provide only local visual cues for perception of spatial depth. (b) Illumination from three orthodirectional light sources with single scattering provides global visual cues but introduces disturbing patterns and is too dark. The same setup visualized with our novel model using (c) a small and (d) a large volumetric region for low-pass filtering to avoid disturbing high-frequency shadow patterns. Abstract—We present a novel and efficient method to compute volumetric soft shadows for interactive direct volume visualization to improve the perception of spatial depth. By direct control of the softness of volumetric shadows, disturbing visual patterns due to hard shadows can be avoided and users can adapt the illumination to their personal and application-specific requirements. We compute the shadowing of a point in the data set by employing spatial filtering of the optical depth over a finite area patch pointing toward each light source. Conceptually, the area patch spans a volumetric region that is sampled with shadow rays; afterward, the resulting optical depth values are convolved with a low-pass filter on the patch. In the numerical computation, however, to avoid expensive shadow ray marching, we show how to align and set up summed area tables for both directional and point light sources. Once computed, the summed area tables enable efficient evaluation of soft shadows for each point in constant time without shadow ray marching and the softness of the shadows can be controlled interactively. We integrated our method in a GPU-based volume renderer with ray casting from the camera, which offers interactive control of the transfer function, light source positions, and viewpoint, for both static and time-dependent data sets. Our results demonstrate the benefit of soft shadows for visualization to achieve user-controlled illumination with many-point lighting setups for improved perception combined with high rendering speed. Index Terms—Direct volume rendering, volume illumination, soft shadows, filtered shadows, summed area table 1

In this article, we present a method for rendering dynamic scenes featuring translucent procedural volumetric detail with all-frequency soft shadows being cast from objects residing inside the view frustum. Our approach is based on an approximation of physically correct shadows from distant Gaussian area light sources positioned behind the view plane, using iterative convolution. We present a theoretical and empirical analysis of this model and propose an efficient class of convolution kernels which provide high quality at interactive frame rates. Our GPU-based implementation supports arbitrary volumetric detail maps, requires no precomputation, and therefore allows for real-time modification of all rendering parameters.

Accepted for publication by IEEE. ©2013 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/

N.B.: When citing this work, cite the original article. ©2011 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et a ̀ la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Figure 1: The user interface and the work flow of the system implementing our proposed method. Four closely linked views are shown and labeled, namely: (1) multi-panel view, (2) volume rendering view, (3) projection view and (4) high-dimensional transfer function view. Three stages: (A) data probing, (B) qualitative analysis and (C) optional feature refinement comprise our work flow. With the proposed method and user interface, domain users are able to explore and extract meaningful features in highly complex multivariate dataset, e.g. the 3D seismic survey shown above. Multivariate volumetric datasets are important to both science and medicine. We propose a transfer function (TF) design approach based on user selected samples in the spatial domain to make mul-tivariate volumetric data visualization more accessible for domain users. Specifically, the user starts the visualization by probing fea-tures of interest on slices and the data values are instantly queried by user selection. The queried sample values are then used to au-tomatically and robustly generate high dimensional transfer func-tions (HDTFs) via kernel density estimation (KDE). Alternatively, 2D Gaussian TFs can be automatically generated in the dimension-ality reduced space using these samples. With the extracted features rendered in the volume rendering view, the user can further refine these features using segmentation brushes. Interactivity is achieved in our system and different views are tightly linked. Use cases show that our system has been successfully applied for simulation and complicated seismic data sets.

Abstract—In this paper, we describe a novel approach for applying texture mapping to volumetric data sets. In contrast to previous approaches, the presented technique enables a unified integration of 2D and 3D textures and thus allows to emphasize material boundaries as well as volumetric regions within a volumetric data set at the same time. One key contribution of this paper is a parametrization technique for volumetric data sets, which takes into account material boundaries and volumetric regions. Using this technique, the resulting parametrizations of volumetric data sets enable texturing effects which create a higher degree of realism in volume rendered images. We evaluate the quality of the parametrization and demonstrate the usefulness of the proposed concepts by combining volumetric texturing with volumetric lighting models to generate photorealistic volume renderings. Furthermore, we show the applicability in the area of illustrative visualization. Index Terms—Volumetric texturing, interactive volume rendering Ç 1