The Perspective Silhouette of a Canal Surface

We present an efficient and robust algorithm for parameterizing the perspective silhouette of a canal surface and detecting each connected component of the silhouette. A canal surface is the envelope of a moving sphere with varying radius, defined by the trajectory C(t) of its center and a radius function r(t) . This moving sphere, S(t) , touches the canal surface at a characteristic circle K(t) . We decompose the canal surface into a set of characteristic circles, compute the silhouette points on each characteristic circle, and then parameterize the silhouette curve. The perspective silhouette of the sphere S(t) from a given viewpoint consists of a circle Q(t) ; by identifying the values of t at which K(t) and Q(t) touch, we can find all the connected components of the silhouette curve of the canal surface. ACM CSS: I.3.7 Computer Graphics–Three Dimensional Graphics and Realism     

Progressive Hulls for Intersection Applications

Progressive meshes are an established tool for triangle mesh simplification. By suitably adapting the simplification process, progressive hulls can be generated which enclose the original mesh in gradually simpler, nested meshes. We couple progressive hulls with a selective refinement framework and use them in applications involving intersection queries on the mesh. We demonstrate that selectively refinable progressive hulls considerably speed up intersection queries by efficiently locating intersection points on the mesh. Concerning the progressive hull construction, we propose a new formula for assigning edge collapse priorities that significantly accelerates the simplification process, and enhance the existing algorithm with several conditions aimed at producing higher quality hulls. Using progressive hulls has the added advantage that they can be used instead of the enclosed object when a lower resolution of display can be tolerated, thus speeding up the rendering process. ACM CSS: I.3.3 Computer Graphics—Picture/Image Generation, I.3.5 Computer Graphics—Computational Geometry and Object Modeling, I.3.7 Computer Graphics—Three‐Dimensional Graphics and Realism     

State‐of‐the‐Art Report on Temporal Coherence for Stylized Animations

Non‐photorealistic rendering (NPR) algorithms allow the creation of images in a variety of styles, ranging from line drawing and pen‐and‐ink to oil painting and watercolour. These algorithms provide greater flexibility, control and automation over traditional drawing and painting. Despite significant progress over the past 15 years, the application of NPR to the generation of stylized animations remains an active area of research. The main challenge of computer‐generated stylized animations is to reproduce the look of traditional drawings and paintings while minimizing distracting flickering and sliding artefacts present in hand‐drawn animations. These goals are inherently conflicting and any attempt to address the temporal coherence of stylized animations is a trade‐off. This state‐of‐the‐art report is motivated by the growing number of methods proposed in recent years and the need for a comprehensive analysis of the trade‐offs they propose. We formalize the problem of temporal coherence in terms of goals and compare existing methods accordingly. We propose an analysis for both line and region stylization methods and discuss initial steps towards their perceptual evaluation. The goal of our report is to help uninformed readers to choose the method that best suits their needs, as well as motivate further research to address the limitations of existing methods.     

3D Video Recorder: a System for Recording and Playing Free‐Viewpoint Video†

We present the 3D Video Recorder, a system capable of recording, processing, and playing three‐dimensional video from multiple points of view. We first record 2D video streams from several synchronized digital video cameras and store pre‐processed images to disk. An off‐line processing stage converts these images into a time‐varying 3D hierarchical point‐based data structure and stores this 3D video to disk. We show how we can trade‐off 3D video quality with processing performance and devise efficient compression and coding schemes for our novel 3D video representation. A typical sequence is encoded at less than 7 Mbps at a frame rate of 8.5 frames per second. The 3D video player decodes and renders 3D videos from hard‐disk in real‐time, providing interaction features known from common video cassette recorders, like variable‐speed forward and reverse, and slow motion. 3D video playback can be enhanced with novel 3D video effects such as freeze‐and‐rotate and arbitrary scaling. The player builds upon point‐based rendering techniques and is thus capable of rendering high‐quality images in real‐time. Finally, we demonstrate the 3D Video Recorder on multiple real‐life video sequences. ACM CSS: I.3.2 Computer Graphics—Graphics Systems, I.3.5 Computer Graphics—Computational Geometry and Object Modelling, I.3.7 Computer Graphics—Three‐Dimensional Graphics and Realism     

Efficient Modeling of An Anatomy-Based Face and Fast 3D Facial Expression Synthesis

This paper presents new methods for efficient modeling and animation of an hierarchical facial model that conforms to the human face anatomy for realistic and fast 3D facial expression synthesis. The facial model has a skin–muscle–skull structure. The deformable skin model directly simulates the nonlinear visco‐elastic behavior of soft tissue and effectively prevents model collapse. The construction of facial muscles is achieved by using an efficient muscle mapping approach. Based on a cylindrical projection of the texture‐mapped facial surface and wire‐frame skin and skull meshes, this approach ensures different muscles to be located at the anatomically correct positions between the skin and skull layers. For computational efficiency, we devise an adaptive simulation algorithm which uses either a semi‐implicit integration scheme or a quasi‐static solver to compute the relaxation by traversing the designed data structures in a breadth‐first order. The algorithm runs in real‐time and has successfully synthesized realistic facial expressions. ACM CSS: I.3.5 Computer Graphics: Computational Geometry and Object Modelling—physically based modelling; I.3.7 Computer Graphics: Three‐Dimensional Graphics and Realism—animation;     

Feature Model Visualization

Feature modelling is now the predominant way of modelling products. Feature visualization is an important aspect here that can still be considerably improved. In this paper, an integrated way of visualizing feature models is presented, using new techniques for both the geometry and the structure of models. For the geometry of feature models, techniques are presented to visualize a selected subset of form features in a way that clearly distinguishes them from the rest of the model, as well as functional information such as closure faces of subtractive form features. For the structure of features models, techniques are presented to visualize several types of graphs. The different visualization techniques are used in an integrated way. Implementation of some of the techniques requires a non‐manifold representation of the geometry of the feature model. This representation, and some other implementation aspects, are briefly described. Throughout the paper, numerous examples of images of feature models are given which show that the new visualization techniques can indeed improve the effectiveness of feature modelling. ACM CSS: I.3.7 Three‐Dimensional Graphics and Realism—visible line/surface algorithms, J.6 Computer‐AidedEngineering—feature modelling     

State of the Art in Global Illumination for Interactive Applications and High-quality Animations

Global illumination algorithms are regarded as computationally intensive. This cost is a practical problem when producing animations or when interactions with complex models are required. Several algorithms have been proposed to address this issue. Roughly, two families of methods can be distinguished. The first one aims at providing interactive feedback for lighting design applications. The second one gives higher priority to the quality of results, and therefore relies on offline computations. Recently, impressive advances have been made in both categories. In this report, we present a survey and classification of the most up‐to‐date of these methods. ACM CSS: I.3.7 Computer Graphics—Three‐Dimensional Graphics and Realism