Physically-Based Patination for Underground Objects

Although current photorealistic rendering techniques can produce very impressive images, the rendered objects are often too clean and shiny. Thus, the resulting images look unnatural. This paper proposes a physically-based model to simulate the appearance of patinas on ancient Chinese bronzes. Buried in the soil for thousands of years, many patinas are found on the surface of ancient bronzes as a result of the aging process and the physical and chemical conditions of the soil environment. The development of patinas is modulated herein by L-systems according to tendencies based on the environmental factors and object geometry. The tendencies are employed to represent the accumulative effect of all factors on patination. The proposed model can be extended to simulate a variety of metallic patinas including the ancient Chinese bronzes discovered at San-hsing-tui, Sichuan, China.     

Priority-Driven Acoustic Modeling for Virtual Environments

Geometric acoustic modeling systems spatialize sounds according to reverberation paths from a sound source to a receiver to give an auditory impression of a virtual 3D environment. These systems are useful for concert hall design, teleconferencing, training and simulation, and interactive virtual environments. In many cases, such as in an interactive walkthrough program, the reverberation paths must be updated within strict timing constraints - e.g., as the sound receiver moves under interactive control by a user. In this paper, we describe a geometric acoustic modeling algorithm that uses a priority queue to trace polyhedral beams representing reverberation paths in best-first order up to some termination criteria (e.g., expired time-slice). The advantage of this algorithm is that it is more likely to find the highest priority reverberation paths within a fixed time-slice, avoiding many geometric computations for lower-priority beams. Yet, there is overhead in computing priorities and managing the priority queue. The focus of this paper is to study the trade-offs of the priority-driven beam tracing algorithm with different priority functions. During experiments computing reverberation paths between a source and a receiver in a 3D building environment, we find that priority functions incorporating more accurate estimates of source-to-receiver path length are more likely to find early reverberation paths useful for spatialization, especially in situations where the source and receiver cannot reach each other through trivial reverberation paths. However, when receivers are added to the environment such that it becomes more densely and evenly populated, this advantage diminishes.     

Floating Points: A Method for Computing Stipple Drawings

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.     

Using an Intermediate Skeleton and Inverse Kinematics for Motion Retargeting

In this paper, we present a new method for solving the Motion Retargeting Problem, by using an intermediate skeleton. This allows us to convert movements between hierarchically and geometrically different characters. An Inverse Kinematics engine is then used to enforce Cartesian constraints while staying as close as possible to the captured motion.     

A Novel Approach Makes Higher Order Wavelets Really Efficient for Radiosity

Since wavelets were introduced in the radiosity algorithm ⁵, surprisingly little research has been devoted to higher order wavelets and their use in radiosity algorithms. A previous study ¹³ has shown that wavelet radiosity, and especially higher order wavelet radiosity was not bringing significant improvements over hierarchical radiosity and was having a very important extra memory cost, thus prohibiting any effective computation. In this paper, we present a new implementation of wavelets in the radiosity algorithm, that is substantially different from previous implementations in several key areas (refinement oracle, link storage, resolution algorithm). We show that, with this implementation, higher order wavelets are actually bringing an improvement over standard hierarchical radiosity and lower order wavelets.     

External Memory View-Dependent Simplification

In this paper, we propose a novel external-memory algorithm to support view-dependent simplification for datasets much larger than main memory. In the preprocessing phase, we use a new spanned sub-meshes simplification technique to build view-dependence trees I/O-efficiently, which preserves the correct edge collapsing order and thus assures the run-time image quality. We further process the resulting view-dependence trees to build the meta-node trees, which can facilitate the run-time level-of-detail rendering and is kept in disk . During run-time navigation, we keep in main memory only the portions of the meta-node trees that are necessary to render the current level of details, plus some prefetched portions that are likely to be needed in the near future. The prefetching prediction takes advantage of the nature of the run-time traversal of the meta-node trees, and is both simple and accurate. We also employ the implicit dependencies for preventing incorrect foldovers, as well as main-memory buffer management and parallel processes scheme to separate the disk accesses from the navigation operations, all in an integrated manner. The experiments show that our approach scales well with respect to the main memory size available, with encouraging preprocessing and run-time rendering speeds and without sacrificing the image quality.     

Towards Blind Detection of Robust Watermarks in Polygonal Models

We describe a Digital Watermarking system dedicated for embedding watermarks into 3D polygonal models. The system consists of three watermarking algorithms, one named Vertex Flood Algorithm (VFA) suitable for embedding fragile public readable watermarks with high capacity and offering a way of model authentication, one realizing affine invariant watermarks, named Affine Invariant Embedding (AIE) and a third one, named Normal Bin Encoding (NBE) algorithm, realizing watermarks with robustness against more complex operations, most noticeably polygon reduction. The watermarks generated by these algorithms are stackable. We shortly discuss the implementation of the system, which is realized as a 3D Studio MAX plugin.     

Modelling virtual cities dedicated to behavioural animation

In order to populate virtual cities, it is necessary to specify the behaviour of dynamic entities such as pedestrians or car drivers. Since a complete mental model based on vision and image processing cannot be constructed in real time using purely geometrical information, higher levels of information are needed in a model of the virtual environment. For example, the autonomous actors of a virtual world would exploit the knowledge of the environment topology to navigate through it. In this article, we present a model of virtual urban environments using structures and information suitable for behavioural animations. Thanks to this knowledge, autonomous virtual actors can behave like pedestrians or car drivers in a complex city environment. A city modeler has been designed, using this model of urban environment, and enables complex urban environments for behavioural animation to be automatically produced.     

Context-based Space Filling Curves

A context-based scanning technique for images is presented. An image is scanned along a context-based space filling curve that is computed so as to exploit inherent coherence in the image. The resulting one-dimensional representation of the image has improved autocorrelation compared with universal scans such as the Peano-Hilbert space filling curve. An efficient algorithm for computing context-based space filling curves is presented. We also discuss the potential of improved autocorrelation of context-based space filling curves for image and video lossless compression.     

Realistic Collision Avoidance of Upper Limbs Based on Neuroscience Models

When articulated figures interact in a 3D environment, collisions are highly likely and must often be avoided. We present a method automatically producing realistic collision-free animation of the upper arms. Based on the latest models of collision avoidance provided by neuroscience, our method allows realistic interpolation of keyframes at interactive speed. In order to validate our scheme we compared computer generated motions with motions performed by a sample of ten humans. These motions were defined by start and final postures and by an obstacle which had to be passed. In each case the generated positions are the same as those chosen by 30% of real humans, we therefore consider our method provides realistic motions. Moreover, the collision-free paths are automatically generated in a few seconds. Hence, our method can be very beneficial to animators by reducing the level of detail needed to define motions of articulated figures. It can also be used for the automatic generation of realistic animations for virtual reality applications.     

Automatic Generation of Virtual Woodblocks and Multicolor Woodblock Printing

In this paper, we study a method to synthesize a multicolor virtual woodblock print by using several virtual woodblocks. It consists of two sections: carving and printing, to synthesize a virtual print. In the carving section, virtual woodblocks are generated by a user with supporting of an automatically carving method based on feature extraction of a gray value image. And woodblocks are also generated automatically by using a full-color image as a draft. In the printing section, a "paper sheet", a "printing brush" and "ink" are prepared in addition to the "woodblock" in the virtual space and the user synthesizes a woodblock print interactively. As the printing factors, a color of ink, a moisture value and a grain change the finish of the print. Using several virtual woodblocks and printing to a paper sheet in succession, a printing image of each woodblock is combined based on the printing factors and a multicolor virtual prints is synthesized.     

Modeling the Motion of Dense Smoke in the Wind Field

This paper presents a volumetric animation technique for modeling the turbulent motion of very dense and turbulent smoke such as one coming from a steam engine. A new method of the wind field generation is proposed. Gas motion is determined by the integration of two independent vector layers. The first one is a combination of flow primitives and the second is created by stochastically generated turbulence. Special attention is taken of the proper construction of the turbulent layer. For the visualization purposes a simple volume raytracer is applied. Many light sources are taken into account to achieve photorealistic effects. Finally some interesting animations are overviewed. Computation times for a PC Pentium 200 and an SGI O2 workstation are compared to demonstrate the high efficiency of the method.     

Scene-Graph-As-Bus: Collaboration between Heterogeneous Stand-alone 3-D Graphical Applications

We describe the Scene-Graph-As-Bus technique (SGAB), the first step in a staircase of solutions for sharing software components for virtual environments. The goals of SGAB are to allow, with minimal effort, independently-designed applications to share component functionality; and for multiple users to share applications designed for single users.This paper reports on the SGAB design for transparently conjoining different applications by unifying the state information contained in their scene graphs. SGAB monitors and maps changes in the local scene graph of one application to a neutral scene graph representation (NSG), distributes the NSG changes over the network to remote peer applications, and then maps the NSG changes to the local scene graph of the remote application. The fundamental contribution of SGAB is that both the local and remote applications can be completely unaware of each other; that is, both applications can interoperate without code or binary modification despite each having no knowledge of networking or interoperability.     

Real Time, Accurate, Multi-Featured Rendering of Bump Mapped Surfaces

We present a new technique to render in real time objects which have part of their high frequency geometric detail encoded in bump maps. It is based on the quantization of normal-maps, and achieves excellent result both in rendering time and rendering quality, with respect to other alternative methods. The method proposed also allows to add many interesting visual effects, even for object with large bumb maps, including non-s rendering, chrome effects, shading under multiple lights, rendering of different materials within a single object, specular reflections and others. Moreover, the implementation of the method is not complex and can be eased by software reuse.     

Binding Virtual Environments to Toolkit Capabilities

There are many toolkits and development environments that aid the process of constructing virtual environment applications. Many of these development environments encourage customising a virtual environment's design while rapid prototyping within the confines of a toolkit's capabilities. Thus the choice of the technology and its associated support has been made independent of the end-use requirements of the final system. This can bias a virtual environment's design by implementation based constraints. We propose that an alternative approach is the consideration of virtual environment requirements in the context of an inspectable design model, to identify the requirements that a toolkit will need to support. In the context of an example, we present a selection of design requirements that we consider important for virtual environment design in general. We explore how these requirements might be mapped to different capabilities using Virtual Reality Modelling Language (VRML) as a concrete example of a platform technology.     

Interpolatory √3-Subdivision

We present a new interpolatory subdivision scheme for triangle meshes. Instead of splitting each edge and performing a 1-to-4 split for every triangle we compute a new vertex for every triangle and retriangulate the old and the new vertices. Using this refinement operator the number of triangles only triples in each step. New vertices are computed with a Butterfly like scheme. In order to obtain overall smooth surfaces special rules are necessary in the neighborhood of extraordinary vertices. The scheme is suitable for adaptive refinement by using an easy forward strategy. No temporary triangles are produced here which allows simpler data structures and makes the scheme easy to implement.     

Augmented Reality with Back-Projection Systems using Transflective Surfaces

In this paper, we introduce the concept of Extended VR (extending viewing space and interaction space of back-projection VR systems), by describing the use of a hand-held semi-transparent mirror to support augmented reality tasks with back-projection systems. This setup overcomes the problem of occlusion of virtual objects by real ones linked with such display systems. The presented approach allows an intuitive and effective application of immersive or semi-immersive virtual reality tasks and interaction techniques to an augmented surrounding space. Thereby, we use the tracked mirror as an interactive image-plane that merges the reflected graphics, which are displayed on the projection plane, with the transmitted image of the real environment. In our implementation, we also address traditional augmented reality problems, such as real-object registration and virtual-object occlusion. The presentation is complemented by a hypothesis of conceivable further setups that apply transflective surfaces to support an Extended VR environment.     

Unsteady Flow Visualization by Animating Evenly-Spaced Streamlines

In recent years the work on vector field visualization has been concentrated on LIC-based methods. In this paper we propose an alternative solution for the visualization of unsteady flow fields. Our approach is based on the computation of temporal series of correlated images. While other methods are based on pathlines and try to correlate successive images at the pixel level, our approach consists in correlating instantaneous visualizations of the vector field at the streamline level. For each frame a feed forward algorithm computes a set of evenly-spaced streamlines as a function of the streamlines generated for the previous frame. This is achieved by establishing a correspondence between streamlines at successive time steps. A cyclical texture is mapped onto every streamline and textures of corresponding streamlines at different time steps are correlated together so that, during the animation, they move along the streamlines, giving the illusion that the flow is moving in the direction defined by the streamline. Our method gives full control on the image density so that we are able to produce smooth animations of arbitrary density, covering the field of representations from sparse, that is classical streamline-based images, to dense, that is texture-like images.     

Subdivision Surface Tesselation on the Fly using a versatile Mesh Data Structure

Subdivision surfaces have become a standard technique for freeform shape modeling. They are intuitive to use and permit designers to flexibly add detail. But with larger control meshes, efficient adaptive rendering techniques are indispensable for interactive visualization and shape modeling. In this paper, we present a realization of tesselation-on-the-fly for Loop subdivision surfaces as part of a framework for interactive visualization.     

Robust Motion Watermarking based on Multiresolution Analysis

Digital watermarking is one of commonly used solutions for copyright protection. A watermark should be imperceptible and robust to various attacks. In this paper, we address watermarking for motion data. Our watermarking scheme is based on two well-known ideas, so called multiresolution representation and spread spectrum. We embed a watermark into a motion signal by perturbing large detail coefficients of its multiresolution representation, and extract the watermark by analyzing perturbation of coefficients from a suspected signal. For more effective watermark extraction, we align suspected motion data to the original using dynamic time warping. Our scheme has merits of spread spectrum such as the resilience to common signal processing as well as the robustness to time warping.