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 curvaturecontrolled style contours and an illustrative transparency model. Our implementation of the presented methods allows interactive generation of high-quality volumetric illustrations. Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism

In this paper we discuss expressive visualization techniques that smartly uncover the most important information in order to maximize the visual information in the resulting images. This is achieved through dynamic changes in visual representations, through deformations, or through spatial modifications of parts of the data. Such techniques originate from technical illustration and are called cut-away views, ghosted views, and exploded views. These illustrative techniques unveil the most important visual information by employing high levels of abstraction. The change in visual representation or spatial position is done easily perceivable and the overall visual harmony is preserved.

Abstract—Volume rendered imagery often includes a barrage of 3D information like shape, appearance and topology of complex structures, and it thus quickly overwhelms the user. In particular, when focusing on a specific region a user cannot observe the relationship between various structures unless he has a mental picture of the entire data. In this paper we present ClearView, a GPU-based, interactive framework for texture-based volume ray-casting that allows users which do not have the visualization skills for this mental exercise to quickly obtain a picture of the data in a very intuitive and user-friendly way. ClearView is designed to enable the user to focus on particular areas in the data while preserving context information without visual clutter. ClearView does not require additional feature volumes as it derives any features in the data from image information only. A simple point-and-click interface enables the user to interactively highlight structures in the data. ClearView provides an easy to use interface to complex volumetric data as it only uses transparency in combination with a few specific shaders to convey focus and context information. Index Terms—Focus & Context, GPU rendering, volume raycasting.

We present the concept of volumetric depth-peeling. The proposed method is conceived to render interior and exterior iso-surfaces for a fixed iso-value and to blend them without the need to render the volume multiple times. The main advantage of our method over pre-integrated volume rendering is the ability to extract arbitrarily many iso-layers for the given iso-value. Up to now, pre-integrated volume rendering is only capable of visualizing the nearest two (front and back-faced) iso-surfaces. A further gain of our algorithm is the rendering speed, since it does not depend on the number of layers to be extracted, as for previous depth-peeling methods. We rather exploit the natural slicing order of 3D texturing to circumvent the handicap of storing intermediate layers in textures, as done in polygonalbased depth-peeling approaches. We are further capable of rapidly previewing the volume data, when only few context information about the concerning dataset is available. An important example of use in the area of non-photorealistic rendering is given, where we can distinguish between visible and hidden silhouettes, which are important elements in stylization. By using standard OpenGL extensions, we allow the exploration of spatial relationships in the volume -at interactive rates- in hardware.

Visualization of volumetric datasets is common in many fields and has been an active area of research in the past two decades. In spite of developments in volume visualization techniques, interacting with large datasets still demands research efforts due to perceptual and performance issues. The support of graphics hardware for texture-based visualization allows efficient implementation of rendering techniques that can be combined with interactive sculpting tools to enable interactive inspection of 3D datasets. In this paper we report the development of three 3D interactive tools, eraser, digger and clipper, which specify regions within the volume to be discarded from rendering. Sculpting is accomplished by running special fragment programs that discard fragments based on geometric predicates. The interaction techniques we proposed were implemented using the virtual hand metaphor. The tools were evaluated by comparing the use of a 3D mouse against a conventional wheelmouse for guiding volume and tools manipulation. Two-handed input was tested with both types of mouse and the results obtained indicate a preference for a combination of 2D and 3D mouse.

Abstract. Recent developments in occlusion management for 3D environments often involve the use of dynamic transparency, or virtual “Xray vision”, to promote target discovery and access in complex 3D worlds. However, there are many different approaches to achieving this effect and their actual utility for the user has yet to be evaluated. Furthermore, the introduction of semi-transparent surfaces adds additional visual complexity that may actually have a negative impact on task performance. In this paper, we report on an empirical user study comparing dynamic transparency to standard viewpoint controls. Our implementation of the technique is an image-space algorithm built using modern programmable shaders to achieve real-time performance and visually pleasing results. Results from the user study indicate that dynamic transparency is superior for perceptual tasks in terms of both efficiency and correctness. 1

Abstract—We present an empirical usability experiment studying the relative strengths and weaknesses of three different occlusion management techniques for discovering and accessing objects in information-rich 3D virtual environments. More specifically, the study compares standard 3D navigation, generalized fisheye techniques using object scaling and transparency, and the BalloonProbe interactive 3D space distortion technique. Subjects are asked to complete a number of representative tasks, including counting, pattern recognition, and object relation, in different kinds of environments and on both immersive and desktop-based VR systems. The environments include a free-space abstract 3D environment and a virtual 3D walkthrough application for a simple building floor. Our results confirm the general guideline that each task calls for a specialized interaction—no single technique performed best across all tasks and worlds. The results also indicate a clear trade-off between speed and accuracy: simple navigation was the fastest but also most error-prone technique, whereas spherical BalloonProbe and transparency-based fisheye proved the most accurate but required longer completion time, making it suitable for applications where mistakes incur a high cost. Index Terms—occlusion reduction, occlusion management, 3D space distortion, interaction techniques, evaluation I.

Combined visualizations of filamentous structures and surrounding volumetric objects are common in biological and medical applications. Often, the structures ’ spatial relationships remain unclear to the viewer. In this paper, we discuss and evaluate techniques to emphasize spatial relationships. We concentrate on the visualization of transparent objects and intersecting lines. Among various techniques, participants of an exploratory user study preferred coloring of lines, marking of line-surface intersections by glyphs, and the combination of both. These techniques were additionally evaluated in a confirmatory study in which participants were asked to judge whether a filament runs through a transparent structure. We found that the evaluated techniques significantly improve the participants ’ performance in terms of the number of correct responses and response time. The best performance was found for the combination of line coloring and intersection glyph display.

Abstract — Recent developments in occlusion management for 3D environments often involve the use of dynamic transparency, or “virtual X-ray vision”, to promote target discovery and access in complex 3D worlds. However, there are many different approaches to achieving this effect and their actual utility for the user has yet to be evaluated. Furthermore, the introduction of semitransparent surfaces adds additional visual complexity that may actually have a negative impact on task performance. In this paper, we report on an empirical user study investigating these human aspects of dynamic transparency. Our implementation of the technique is an image-space algorithm built using modern programmable shaders to achieve real-time performance and visually pleasing results. Results from the user study indicate that dynamic transparency provides superior performance for perceptual tasks in terms of both efficiency and correctness. Subjective ratings are also firmly in favor of the method. Index Terms—About four key words or phrases in alphabetical order, separated by commas. I.

Abstract not found