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Now showing 1 - 10 of 12
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    Guided Exploration with Dynamic Potential Fields: the Cubical Path System
    (Blackwell Publishers Ltd and the Eurographics Association, 2001) Beckhaus, Steffi; Ritter, Felix; Strothotte, Thomas
    Exploring unknown models or scenes is a highly interactive and dynamic process. Systems for automatic presentation of models or scenes either require cinematographic rules, direct human interaction, framesets, or pre-calculation of paths to a known goal. In this paper we present a system which can deal with rapidly changing user interest in objects of a scene or model as well as with dynamic models and changes of the camera position introduced interactively by the user or through cuts. We describe CubicalPath, a new potential field-based camera control system that helps with the exploration of virtual environments.
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    How to Render Frames and Influence People
    (Blackwell Science Ltd and the Eurographics Association, 1994) Strothotte, Thomas; Preim, Bernhard; Raab, Andreas; Schumann, Jutta; Forsey, David R.
    Rendering systems generally treat the production of images as an objective process governed by the laws of physics. However, perception and understanding on the part of viewers are subjective processes influenced by a variety offactors. For example, in the presentation of architectural drawings, the apparent precision with which the drawings are made will affect whether the viewer considers the design as part of a preliminary design or as part of a final polished project, and to some extent the level of confidence the viewer has in the encoded information.In this paper we develop techniques for rendering images in a way that differs from the usual photorealistic or wire-frame output of renderers. In particular, our techniques allow a user to adjust the rendering of a scene to produce images using primitives with variable degrees of precision, from approximations that resemble vague"five-minute-sketches" to more mature but still hand-drawn images. We provide a theoretical framework for analysing the information flow from the computer to the user via such images. Finally, we describe the design and implementation of a prototypical renderer and show examples of its output.
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    Floating Points: A Method for Computing Stipple Drawings
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Deussen, Oliver; Hiller, Stefan; Van Overveld, Cornelius; Strothotte, Thomas
    We present a method for computer generated pen-and-ink illustrations by the simulation of stippling. In a stipple drawing, dots are used to represent tone and also material of surfaces. We create such drawings by generating an initial dot set which is then processed by a relaxation method based on Voronoi diagrams. The point patterns generated are approximations of Poisson disc distributions and can also be used for integrating functions or the positioning of objects. We provide an editor similar to paint systems for interactively creating stipple drawings. This makes it possible to create such drawings within a matter of hours, instead of days or even weeks when the drawing is done manually.
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    Real-Time Halftoning: A Primitive For Non-Photorealistic Shading
    (The Eurographics Association, 2002) Freudenberg, Bert; Masuch, Maic; Strothotte, Thomas; P. Debevec and S. Gibson
    We introduce halftoning as a general primitive for real-time non-photorealistic shading. It is capable of producing a variety of rendering styles, ranging from engraving with lighting-dependent line width to pen-and-ink style drawings using prioritized stroke textures. Since monitor resolution is limited we employ a smooth threshold function that provides stroke antialiasing. By applying the halftone screen in texture space and evaluating the threshold function for each pixel we can influence the shading on a pixel-by-pixel basis. This enables many effects to be used, including indication mapping and individual stroke lighting. Our real-time halftoning method is a drop-in replacement for conventional multitexturing and runs on commodity hardware. Thus, it is easy to integrate in existing applications, as we demonstrate with an artistically rendered level in a game engine.
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    Stylizing Silhouettes at Interactive Rates: From Silhouette Edges to Silhouette Strokes
    (Blackwell Publishers, Inc and the Eurographics Association, 2002) Isenberg, Tobias; Halper, Nick; Strothotte, Thomas
    A way to create effective stylized line drawings is to draw strokes that start and stop at visible portions along the silhouette of an object to be portrayed. In computer graphics to date, algorithms to extract silhouette edges are many, although putting these edges into a form such that stylized strokes may be applied to them has not been greatly covered, so that existing methods are either time-consuming or presented vaguely. In this paper, we introduce an algorithm that takes a set of silhouette edges originating from polygonal meshes and efficiently computes the visible parts of the edges before connecting them to form long smooth silhouette strokes to which stylization algorithms may be effectively applied. Features of our algorithm that gain efficiency and accuracy over existing methods is that we directly exploit the analytic connectivity information of the mesh in combination with the availablez-bufferinformation during rendering, and filter artifacts in connected edges during the process to improve the visual quality of strokes after stylization.Categories and Subject Descriptors (according to ACM CCS):1.3.3 [Computer Graphics]: Picture/Image Generation-Line and curve generation1.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism-Hidden line/surface removal
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    A Camera Engine for Computer Games: Managing the Trade-Off Between Constraint Satisfaction and Frame Coherence
    (Blackwell Publishers Ltd and the Eurographics Association, 2001) Halper, Nicolas; Helbing, Ralf; Strothotte, Thomas
    Many computer games treat the user in the "1st person" and bind the camera to his or her view. More sophistication in a game can be achieved by enabling the camera to leave the users' viewpoint. This, however, requires new methods for automatic, dynamic camera control. In this paper we present methods and tools for such camera control. We emphasize guiding camera control by constraints; however, optimal constraint satisfaction tends to lead to the camera jumping around too much. Thus, we pay particular attention to a trade-off between constraint satisfaction and frame coherence. We present a new algorithm for dynamic consideration of the visibility of objects which are deemed to be important in a given game context.
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    Approximated View Reconstruction Using Precomputed ID-Bitfields
    (Eurographics Association, 2001) Meruvia Pastor, Oscar E.; Strothotte, Thomas
    A technique is presented to construct arbitrary views of a model by using previously computed views. The technique is simple to implement, completely general for polygonal models and can be used within object hierarchies or scene graphs. During a preprocessing step images of a model are taken from different viewpoints. These images are saved using long bitfields (ID-bitfields) which encode the visibility information according to an array of the model’s primitives used as the base for the bitfield. These ID-bitfield encodings, together with the primitive array, are then used by a viewer which selects and joins them to provide an approximated (not conservative) reconstruction of the visible elements of the object for a new viewpoint. The technique implicitly performs occlusion culling, since a minimal set of visible polygons is the result of the reconstruction. Results show how interaction can be improved when working with high depth complexity models. Satisfactory reconstructions are achieved by taking as few as 25 images around an object. This paper suggests how the technique can be extended to other applications such as virtual walkthroughs and visualization of non-realistic images, and how graphics libraries and hardware could be enhanced by allowing the application to pass an ID-bitfield. Key words: view reconstruction, interactive display, visibility preprocessing, occlusion culling, polygon reduction.
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    Frame-Coherent Stippling
    (Eurographics Association, 2002) Meruvia Pastor, Oscar E.; Strothotte, Thomas
    Stippling is an artistic rendering technique where shading and texture is given by placing points or stipples on the canvas until the desired darkness is achieved. Computer-generated stippling has focused on producing high quality 2D renditions for print media, while stippling of 3D models in animation has received little attention. In this paper we present a technique to produce frame-coherent animations of 3D models using stippling as a rendering style. The problem for which we provide a solution is how to obtain an even distribution of stipples and at the same time ensure frame-to-frame coherence while shading changes over time. In our approach, particles are placed on the surface of the 3D model and adaptively rendered as stipples using OpenGL point primitives and the input model as a canvas. At each frame, the density of particles can be increased if necessary. Selection of particles during rendering takes into account the screen space projection of the edges of a polygon fan that surrounds the particles and the desired tone at the position of the particles. The rendering technique presented here can be applied to arbitrary polygonal meshes and can be extended to include grey scale textures, bump mapping and custom illumination models.
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    RenderBots-Multi-Agent Systems for Direct Image Generation
    (The Eurographics Association and Blackwell Publishing Ltd., 2005) Schlechtweg, Stefan; Germer, Tobias; Strothotte, Thomas
    The term stroke-based rendering collectively describes techniques where images are generated from elements that are usually larger than a pixel. These techniques lend themselves well for rendering artistic styles such as stippling and hatching. This paper presents a novel approach for stroke-based rendering that exploits multi-agent systems. RenderBots are individual agents each of which in general represents one stroke. They form a multi-agent system and undergo a simulation to distribute themselves in the environment. The environment consists of a source image and possibly additional G-buffers. The final image is created when the simulation is finished by having each RenderBot execute its painting function. RenderBot classes differ in their physical behavior as well as their way of painting so that different styles can be created in a very flexible way.
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    Walk-Through Illustrations: Frame-Coherent Pen-and-Ink Style in a Game Engine
    (Blackwell Publishers Ltd and the Eurographics Association, 2001) Freudenberg, Bert; Masuch, Maic; Strothotte, Thomas
    In this paper we show how a game engine designed to generate photorealistic images can be extended to produce non-photorealistic and hybrid renditions. We introduce new hardware-based methods to accomplish pen-and-ink illustrations. The combination of the highly optimized processing of a game engine and the use of hardware for NPR algorithms yields real-time animation of pen-and-ink illustrations.The particular advance of this method is that it yields the first real-time, frame-coherent pen-and-ink animations which maintain both tone and texture.