Volume 16 (1997)
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Item Interactive High-Quality Soft Shadows in Scenes with Moving Objects(Blackwell Publishers Ltd and the Eurographics Association, 1997) Loscos, Celine; Drettakis, GeorgeInteractive rendering of soft shadows (or penumbra) in scenes with moving objects is a challenging problem. High quality walkthrough rendering of static scenes with penumbra can be achieved using pre-calculated discontinuity meshes, which provide a triangulation well adapted to penumbral boundaries, and backprojections which provide exact illumination computation at vertices very efficiently. However, recomputation of the complete mesh and back-projection structures at each frame is prohibitively expensive in environments with changing geometry. This recomputation would in any case be wasteful: only a limited part of these structures actually needs to be recalculated. We present a novel algorithm which uses spatial coherence of movement as well as the rich visibility information existing in the discontinuity mesh to avoid unnecessary recomputation after object motion. In particular we isolate all modifications required for the update of the discontinuity mesh by using an augmented spatial subdivision structure and we restrict intersections of discontinuity surfaces with the scene. In addition, we develop an algorithm which identifies visibility changes by exploiting information contained in the planar discontinuity mesh of each scene polygon, obviating the need for many expensive searches in 3D space. A full implementation of the algorithm is presented, which allows interactive updates of high-quality soft shadows for scenes of moderate complexity. The algorithm can also be directly applied to global illumination.Item Join Now!(Blackwell Publishers Ltd and the Eurographics Association, 1997)Item Fourth Eurographics Workshop on Graphics and Visualization Education (GVE):Poitiers, France, August 24-25, 1996(Blackwell Publishers Ltd and the Eurographics Association, 1997)Item Image Credit to G. Elber(Blackwell Publishers Ltd and the Eurographics Association, 1997) Gibson, S.; Hubbold, R. J.Item Painting-like Image Emphasis based on Human Vision Systems(Blackwell Publishers Ltd and the Eurographics Association, 1997) Tanaka, Toshimitsu; Ohnishi, NoboruRegional image emphasis is often evident in paintings and illustrations. This technique increases local contrast while reducing global contrast by amplifying image intensity on shadowed surfaces, reducing intensity on illuminated surfaces, and then expanding contrast at intensity edges. The effects are assumed to result from the visual processing needed to interpolate the real world onto canvas. Therefore, we propose an intensity emphasis method based on human vision. This method simulates the adaptation of photoreceptor cells and the lateral inhibition of receptive fields. These attributes of a vision system are realized by computation of relative intensity and differential intensity in small areas.The proposed method can successfully generate painting-like artifacts, which greatly improves the perception of visual elements displayed in an image. Since the method efficiently reduces the dynamic range of images, it can be used for displaying highlighted images on standard graphic monitors. Experiments on a computer-generated image and a photograph confirm the advantages of our method.Item Interactive Boundary Computation of Boolean Combinations of Sculptured Solids(Blackwell Publishers Ltd and the Eurographics Association, 1997) Krishnan, S.; Gopi, M.; Manocha, D.; Mine, M.We present algorithms and systems for interactive boundary computation of Boolean combinations of sculptured solids. The algorithm is applicable to all spline solids and computes an accurate boundary representation. To speed up the computation, the algorithm exploits parallelism at all stages. It has been implemented on a multi-processor SGI and takes one second on average per boolean operation to compute the boundary of high degree primitives. The system has also been integrated with an immersive design and manipulation environment. The resulting system is able to interactively evaluate boundaries of the models, display them for model validation and place them at appropriate position using collision detection algorithms.Item Eurographics'98(Blackwell Publishers Ltd and the Eurographics Association, 1997)Item Radiosity with Well Distributed Ray Sets(Blackwell Publishers Ltd and the Eurographics Association, 1997) Neumann, Laszlo; Neumann, Attila; Bekaert, PhilippeIn this paper we present a new radiosity algorithm, based on the notion of a well distributed ray set (WDRS). A WDRS is a set of rays, connecting mutually visible points and patches, that forms an approximate representation of the radiosity operator and the radiosity distribution. We propose an algorithm that constructs an optimal WDRS for a given accuracy and mesh. The construction is based on discrete importance sampling as in previously proposed stochastic radiosity algorithms, and on quasi Monte Carlo sampling. Quasi Monte Carlo sampling leads to faster convergence rates and the fact that the sampling is deterministic makes it possible to represent the well distributed ray set very efficiently in computer memory. Like previously proposed stochastic radiosity algorithms, the new algorithm is well suited for computing the radiance distribution in very complex diffuse scenes, when it is not feasible to explicitly compute and store form factors as in classical radiosity algorithms. Experiments show that the new algorithm is often more efficient than previously proposed Monte Carlo radiosity algorithms by half an order of magnitude and more.Item Rendering Caustics on Non-Lambertian Surfaces(Blackwell Publishers Ltd and the Eurographics Association, 1997) Jensen, Henrik WannThis paper presents a new technique for rendering caustics on non-Lambertian surfaces. The method is based on an extension of the photon map which removes previous restrictions limiting the usage to Lambertian surfaces. We add information about the incoming direction to the photons and this allows us to combine the photon map with arbitrary reflectance functions. By using a cone-filter we improve the quality of the radiance estimate in particular at discontinuities. Furthermore we introduce balancing of the photon map which not only reduces the memory requirements but also significantly reduces the rendering time. We have used the method to render caustics on surfaces with reflectance functions varying from Lambertian to glossy specular.Item 1998 Cover Competition(Blackwell Publishers Ltd and the Eurographics Association, 1997)Item Calendar of Events(Blackwell Publishers Ltd and the Eurographics Association, 1997)Item Fifteenth Annual Conference Eurographics UK â 97: University of East Anglia, Norwich, March 24-26, 1997(Blackwell Publishers Ltd and the Eurographics Association, 1997)Item 5th EG Workshop on DSV-IS: call for participation(Blackwell Publishers Ltd and the Eurographics Association, 1997)Item Join Now!(Blackwell Publishers Ltd and the Eurographics Association, 1997)Item General Assembly minutes(Blackwell Publishers Ltd and the Eurographics Association, 1997)Item Finally Everyone Can Work With Highly Complex 3D Models(Blackwell Publishers Ltd and the Eurographics Association, 1997) Rossignac, JarekIn the past, access to 3D databases was restricted to few specialists having the appropriate CAD skills, software, and graphics hardware.The availability of inexpensive graphics support on personal computers, the Internetâ s impact on private and commercial communication, and the emergence of multimedia standards provide the basis for linking CAD databases with other personal productivity and communication tools and for making them accessible to everyone at home, in schools, in hospitals, or in the industry. For example, employees that have no design expertise, customers, and suppliers would benefit from having an easy access to the 3D databases of a company for: collaborative design review, 3D-based multi-media problem reports, collaborative problem solving and tracking, online training and documentation, internet-based part purchasing and subcontracting, demonstration to customers, or advertising. This presentation will address three of the key issues that have so far limited the non-specialistâ s access to 3D databases.First-time or occasional non-expert users need to become instant experts in 3D navigation through Virtual Environments or in the interactive manipulation of digital 3D models, so that they may immediately focus on their tasks, and not waste precious time learning and fighting an unnatural user interface. Immersive VR is not the panacea - other more effective techniques show promise.The data complexity found in commercial CAD databases, especially in the automotive, aerospace, and construction industries, significantly exceeds the capabilities of any interactive graphics system. This situation is not likely to change, since the growth of the complexity and availability of 3D models outpaces the performance improvement of personal computers. Research on the automatic simplification of 3D models and on the use of levels of detail to accelerate the rendering of distant portions of the scene is growing rapidly.The still limited bandwidth of internet communication channels prohibits a pervasive access to large amounts of 3D data. Recent 3D compression techniques reduce the storage requirements for polyhedral 3D models by two orders of magnitudes.Item Bounded Radiosity - Illumination on General Surfaces and Clusters(Blackwell Publishers Ltd and the Eurographics Association, 1997) Stamminger, Marc; Slusallek, Philipp; Seidel, Hans-PeterTraditionally, Radiosity algorithms have been restricted to scenes made from planar patches. Most algorithms for computing form factors and the subdivision criterion for hierarchical methods implicitly assume planar patches. In this paper, we present a new radiosity algorithm that is solely based on simple geometric information about surface elements, namely their bounding boxes and cone of normals. Using this information allows to compute efficient error bounds that can be used for the subdivision oracle and for computing the energy transfer. Due to the simple interface to geometric objects, our algorithm not only allows for computing illumination on general curved surfaces, but it can also be directly applied to a hieararchy of clusters. Several examples demonstrate the advantages of the new approach.Item Book Reviews(Blackwell Publishers Ltd and the Eurographics Association, 1997)Item Eighth Eurographics Workshop on Visualization in Scientific Computing: Boulogne-sur-Mer, France, April 28-30, 1997(Blackwell Publishers Ltd and the Eurographics Association, 1997)Item Robust Computation of Intersection Graph between Two Solids(Blackwell Publishers Ltd and the Eurographics Association, 1997) Nakamura, Hiroyuki; Higashi, Masatake; Hosaka, MamoruWe propose a new robust algorithm for Boolean operations on solid models. The algorithm produces a consistent intersection graph between two input solids whose geometrical data are represented in floating point numbers. In order to prevent numerical calculation errors and inaccuracy of input data from causing inconsistency of the output, we put higher priority on symbolical connectivity of the edge-face intersection points than their numerical nearness. Each edge-face intersection point is symbolically represented using face names, which generate connectivity relations between the intersection points and the intersection line segments. The symbols with the same connectivity are made into clusters. The intersection line segments connected together at their end clusters form the intersection graph of two solids. Inconsistency of the connectivity of the clusters is detected and the intersection graph is corrected automatically. We describe the algorithm in detail for polyhedral solids, discuss extension to curves solids, and show its effectiveness by some examples of Boolean operations for two solids whose faces intersect at a very small angle.