@misc{HombergBaumWiebeletal., author = {Homberg, Ulrike and Baum, Daniel and Wiebel, Alexander and Prohaska, Steffen and Hege, Hans-Christian}, title = {Definition, Extraction, and Validation of Pore Structures in Porous Materials}, issn = {1438-0064}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-42510}, abstract = {An intuitive and sparse representation of the void space of porous materials supports the efficient analysis and visualization of interesting qualitative and quantitative parameters of such materials. We introduce definitions of the elements of this void space, here called pore space, based on its distance function, and present methods to extract these elements using the extremal structures of the distance function. The presented methods are implemented by an image processing pipeline that determines pore centers, pore paths and pore constrictions. These pore space elements build a graph that represents the topology of the pore space in a compact way. The representations we derive from μCT image data of realistic soil specimens enable the computation of many statistical parameters and, thus, provide a basis for further visual analysis and application-specific developments. We introduced parts of our pipeline in previous work. In this chapter, we present additional details and compare our results with the analytic computation of the pore space elements for a sphere packing in order to show the correctness of our graph computation.}, language = {en} } @misc{WiebelVosHege, author = {Wiebel, Alexander and Vos, Frans M. and Hege, Hans-Christian}, title = {Perception-Oriented Picking of Structures in Direct Volumetric Renderings}, issn = {1438-0064}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-14343}, number = {11-45}, abstract = {Radiologists from all application areas are trained to read slice-based visualizations of 3D medical image data. Despite the numerous examples of sophisticated three-dimensional renderings, especially all variants of direct volume rendering, such methods are often considered not very useful by radiologists who prefer slice-based visualization. Just recently there have been attempts to bridge this gap between 2D and 3D renderings. These attempts include specialized techniques for volume picking that result in repositioning slices. In this paper, we present a new volume picking technique that, in contrast to previous work, does not require pre-segmented data or metadata. The positions picked by our method are solely based on the data itself, the transfer function and, most importantly, on the way the volumetric rendering is perceived by viewers. To demonstrate the usefulness of the proposed method we apply it for automatically repositioning slices in an abdominal MRI scan, a data set from a flow simulation and a number of other volumetric scalar fields. Furthermore we discuss how the method can be implemented in combination with various different volumetric rendering techniques.}, language = {en} } @misc{StoppelHegeWiebel, author = {Stoppel, Sergej and Hege, Hans-Christian and Wiebel, Alexander}, title = {Visibility-Driven Depth Determination of Surface Patches in Direct Volume Rendering}, issn = {1438-0064}, doi = {10.2312/eurovisshort.20141164}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-50266}, abstract = {This paper presents an algorithm called surfseek for selecting surfaces on the most visible features in direct volume rendering (DVR). The algorithm is based on a previously published technique (WYSIWYP) for picking 3D locations in DVR. The new algorithm projects a surface patch on the DVR image, consisting of multiple rays. For each ray the algorithm uses WYSIWYP or a variant of it to find the candidates for the most visible locations along the ray. Using these candidates the algorithm constructs a graph and computes a minimum cut on this graph. The minimum cut represents a very visible but relatively smooth surface. In the last step the selected surface is displayed. We provide examples for the results in real-world dataset as well as in artificially generated datasets.}, language = {en} } @misc{WiebelPreisVosetal., author = {Wiebel, Alexander and Preis, Philipp and Vos, Frans M. and Hege, Hans-Christian}, title = {Computation and Application of 3D Strokes on Visible Structures in Direct Volume Rendering}, issn = {1438-0064}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-18070}, abstract = {In this paper we describe VisiTrace, a novel technique to draw 3D lines in 3D volume rendered images. It allows to draw strokes in the 2D space of the screen to produce 3D lines that run on top or in the center of structures actually visible in the volume rendering. It can handle structures that only shortly occlude the structure that has been visible at the starting point of the stroke and is able to ignore such structures. For this purpose a shortest path algorithm finding the optimal curve in a specially designed graph data structure is employed. We demonstrate the usefulness of the technique by applying it to MRI data from medicine and engineering, and show how the method can be used to mark or analyze structures in the example data sets, and to automatically obtain good views toward the selected structures.}, language = {en} }