Abstract—Volumetric data commonly has high depth complexity which makes it difficult to judge spatial relationships accurately. There are many different ways to enhance depth perception, such as shading, contours, and shadows. Artists and illustrators frequently employ halos for this purpose. In this technique, regions surrounding the edges of certain structures are darkened or brightened which makes it easier to judge occlusion. Based on this concept, we present a flexible method for enhancing and highlighting structures of interest using GPU-based direct volume rendering. Our approach uses an interactively defined halo transfer function to classify structures of interest based on data value, direction, and position. A feature-preserving spreading algorithm is applied to distribute seed values to neighboring locations, generating a controllably smooth field of halo intensities. These halo intensities are then mapped to colors and opacities using a halo profile function. Our method can be used to annotate features at interactive frame rates. Index Terms—Volume rendering, illustrative visualization, halos. 1

In this state-of-the-art report we discuss relevant research works related to the visualization of complex, multivariate data. We discuss how different techniques take effect at specific stages of the visualization pipeline and how they apply to multi-variate data sets being composed of scalars, vectors and tensors. We also provide a categorization of these techniques with the aim for a better overview of related approaches. Based on this classification we highlight combinable and hybrid approaches and focus on techniques that potentially lead towards new directions in visualization research. In the second part of this paper we take a look at recent techniques that are useful for the visualization of complex data sets either because they are general purpose or because they can be adapted to specific problems.

We present an accurate, interactive silhouette extraction mechanism for texture-based volume rendering. Compared to previous approaches, our system guarantees silhouettes of a user controlled width without any significant preprocessing time. Our visualization pipeline consists of two steps: (a) extraction of silhouettes with a width of one pixel, and (b) image post-processing for broadening of silhouettes. Step (a) is a mixture of object- and image-based- silhouette extraction models, maximally exploiting the screen resolution. This hybrid approach is neither sensitive to accuracy in gradient representation nor to the precision of the depth-buffer, as in earlier procedures. Step (b) is accomplished via smoothing and applying a threshold to the temporary result obtained in (a). To keep the latter process efficient, we perform fast convolution using FFT. Our silhouette extraction is conceptually similar to the corresponding method for polygonal representations, checking the front-and back facing property of adjacent triangles.

In this paper, we present a multi-modal data perceptualization system used to analyze the benefits of augmenting a volume docking problem with other perceptual cues, particularly stereoscopic vision and haptic rendering. This work focuses on the problem of matching complex threedimensional shapes in order to reproduce known configurations. Specifically, we focus on the docking of two proteins, actin and cofilin, responsible for cellular locomotion. Users were shown examples of cofilin combining with actin and asked to reproduce this match. Accuracy of the match and completion time were measured and analyzed in order to quantify the benefits of augmenting tools for such a task. 1.

Abstract—Conveying shape using feature lines is an important visualization tool in visual computing. The existing feature lines (e.g., ridges, valleys, silhouettes, suggestive contours, etc.) are solely determined by local geometry properties (e.g., normals and curvatures) as well as the view position. This paper is strongly inspired by the observation in human vision and perception that a sudden change in the luminance plays a critical role to faithfully represent and recover the 3D information. In particular, we adopt the edge detection techniques in image processing for 3D shape visualization and present Photic Extremum Lines (PELs) which emphasize significant variations of illumination over 3D surfaces. Comparing with the existing feature lines, PELs are more flexible and offer users more freedom to achieve desirable visualization effects. In addition, the user can easily control the shape visualization by changing the light position, the number of light sources, and choosing various light models. We compare PELs with the existing approaches and demonstrate that PEL is a flexible and effective tool to illustrate 3D surface and volume for visual computing. Index Terms—Surface and volume illustration, illumination, photic extremum lines (PELs), silhouettes, suggestive contours, ridges and valleys, digital geometry processing. 1

Previous work has demonstrated the clarity and usefulness of illustrative techniques for visualizing flow data. However, previous systems were limited to applying these techniques to uniform grids. Since unstructured grids have emerged as a common basis for computing flow simulations, we present a method to apply and extend the flow illustration approach to tetrahedral meshes using pre-integrated GPU-accelerated raycasting. Our illustrative rendering techniques can also be applied for other pre-integrated volume rendering systems. Additionally, we explore new feature illustration techniques for flow visualization. Categories and Subject Descriptors (according to ACM CCS): I.3.6 [Computer Graphics]: Interaction techniques; I.3.7 [Computer Graphics]: Color, shading;

In this state-of-the-art report we discuss relevant research works related to the visualization of complex, multivariate data. We focus on ”non-classical ” approaches, i.e. approaches which haven’t been discussed in previous related reports, and we highlight techniques which potentially lead towards new directions in visualization research. We discuss how different techniques take effect at specific stages of the visualization pipeline and how they apply to multi-variate data sets being composed of scalars, vectors, and tensors. We also provide a categorization of these techniques in the aim for a better overview of related approaches. In the second part of this paper we take a look at recent techniques that are useful for the visualization of complex data sets either because they are general purpose or because they can be adapted to specific problems. 1.

In many interactive scenarios, the fast recognition and localization of crucial information is very important to effectively perform a task. However, in information visualization the visualization of permanently growing large data volumes often leads to a simultaneously growing amount of presented graphical primitives. Besides the fundamental problem of limited screen space, the effective localization of single or multiple items of interest by a user becomes more and more difficult. Therefore, different approaches have been developed to emphasize those items – mainly by manipulating the items size, by suppressing the whole context or by adding supplemental visual elements (e.g., contours, arrows). This paper introduces the well known illustrative technique of haloing to information visualization to address the localization problem. Applying halos emphasizes items without a manipulation of size or an introduction of additional visual elements and reduces the context suppression to a locally defined region. This paper also presents the results of a first user-study to get an impression of the usefulness of halos for a faster recognition.

Silhouettes play a crucial role in visualization, graphics and vision. This work focuses on the global behaviors and aspect graphs in computer vision. of silhouettes, especially their topological evolutions, such Silhouettes are one of the major research focuses in Nonas their splitting, merging, appearing and disappearing. The Photorealistic Rendering in graphics. For human visual per-dynamics of silhouettes are governed by the topology, the ception, silhouettes carry the most important shape infor-curvature of the surface, and the viewpoint. mation. Accurately and efficiently computing the silhouettes Some theoretical results are established: the integration has attracted many researchers. In order to improve the effi-of signed geodesic curvature along a silhouette is equal to ciency of computing silhouettes, it is highly desirable to in-the view cone angle; critical events can only happen when terpolate silhouettes from pre-computed ones when the view the view point is on the aspect surfaces (ruled surface of the is moved between sampled views. If the topological struc-asymptotic lines of parabolic points). tures of the pre-computed silhouettes are consistent, the in-We introduce a method to visualize the evolution of silterpolation is sensible and easy to perform. Therefore, it is houettes, especially all the critical events where the topolo- critical to fully understand the topological evolutions of silgies of the silhouettes change. The results have broad aphouettes when the view point is moved in space. plications in computer vision for recognition, graphics for The major goal of this work is to study when, where, rendering and visualization. and how the topologies of the silhouettes will change, along