A dynamic animation engine for generic spline objects

This paper introduces an accurate and efficient engine whose purpose is the dynamic animation of curvilinear objects which are modelled as successions of splines. At each time step the object shape conforms to its spline definitions, thus ensuring that each property implied by the chosen spline models is verified. This is achieved by animating spline control points. However, these control points are not considered as material points but rather as the degrees of freedom of the continuous object. The chosen dynamic equations (Lagrangian formalism) reflect this modelling scheme and yield an exact and very proficient linear system. In the chosen formalism, forces are introduced by either their potential energy or their power ratings in the virtual movements instilled by the degrees of freedom. Both methods are carried out in three cases: gravity, viscosity and generic force. Suitable and classical methods for constraint handling and numerical resolution are briefly discussed. Finally, this animation engine is applied to knitted patterns. Copyright © 2000 John Wiley & Sons, Ltd.     

Joining polyhedral objects using implicitly defined surfaces

Published online: 2 October 2001     

Image-based animation of facial expressions

We present a novel technique for creating realistic facial animations given a small number of real images and a few parameters for the in-between images. This scheme can also be used for reconstructing facial movies where the parameters can be automatically extracted from the images. The in-between images are produced without ever generating a three-dimensional model of the face. Since facial motion due to expressions are not well defined mathematically our approach is based on utilizing image patterns in facial motion. These patterns were revealed by an empirical study which analyzed and compared image motion patterns in facial expressions. The major contribution of this work is showing how parameterized “ideal” motion templates can generate facial movies for different people and different expressions, where the parameters are extracted automatically from the image sequence. To test the quality of the algorithm, image sequences (one of which was taken from a TV news broadcast) were reconstructed, yielding movies hardly distinguishable from the originals. Published online: 2 October 2002 Correspondence to: A. Tal Work has been supported in part by the Israeli Ministry of Industry and Trade, The MOST Consortium     

Analysis of numerical methods for the simulation of deformable models

Simulating deformable objects based on physical laws has become the most popular technique for modeling textiles, skin, or volumetric soft objects like human tissue. The physical model leads to an ordinary differential equation. Recently, several approaches to fast algorithms have been proposed.In this work, more profound numerical background about numerical stiffness is provided. Stiff equations impose stability restrictions on a numerical integrator. Some one-step and multistep methods with adequate stability properties are presented. For an efficient implementation, the inexact Newton method is discussed. Applications to 2D and 3D elasticity problems show that the discussed methods are faster and give higher-quality solutions than the commonly used linearized Euler method.     

Layered animation of captured data

normal volume of a triangle to convert individual triangles to a volumetric representation. A layered model is constructed to animate the reconstructed high-resolution surface. The model consists of 3 layers: a skeleton for animation from key-frame or motion capture; a low-resolution control model for real-time mesh deformation; and a high-resolution model to represent the captured surface detail. Initially the skeleton model is manually placed inside the low-resolution control model and high-resolution scanned data. Automatic techniques are introduced to map both the control model and captured data into a single layered model. The high-resolution captured data is mapped onto the low-resolution control model using the normal volume. The resulting model enables efficient, seamless animation by manipulation of the skeleton while maintaining the captured high-resolution surface detail. The animation of high-resolution captured data based on a low-resolution generic model of the object opens up the possibility of rapid capture and animation of new objects based on libraries of generic models. Published online: 2 October 2001     

Survey on model-based manipulation planning of deformable objects

A systematic overview on the subject of model-based manipulation planning of deformable objects is presented. Existing modeling techniques of volumetric, planar and linear deformable objects are described, emphasizing the different types of deformation. Planning strategies are categorized according to the type of manipulation goal: path planning, folding/unfolding, topology modifications and assembly. Most current contributions fit naturally into these categories, and thus the presented algorithms constitute an adequate basis for future developments.     

A deformable model of the human iris for measuring small three-dimensional eye movements

This paper describes a deformable model of the human iris which forms part of a system for accurate off-line measurement of binocular three-dimensional eye movements, particularly cyclotorsion (torsion), from video image sequences. At least two existing systems measure torsion from infrared video images by pupil tracking followed by cross correlation using arcs of bandpass-filtered iris texture. Unfortunately, pupil expansion and contraction reduces the accuracy of this method unless drugs are used to constrict the pupil, which causes temporary blurred vision. A five-parameter deformable model of the iris is therefore developed for analysing images obtained without the use of drugs. This model can translate (horizontal and vertical eye motion), rotate (torsion) and scale both uniformly and radially (pupil changes). Torsion measurements obtained with the model are repeatable and accurate to within 0.1°; this performance is illustrated by analysing binocular torsion during fixation on a stationary target. Received: 27 August 1997 / Accepted: 15 January 1998     

An efficient animation of wrinkled cloth with approximate implicit integration

This paper presents an efficient method for creating the animation of flexible objects. The mass-spring model was used to represent flexible objects. The easiest approach to creating animation with the mass-spring model is the explicit Euler method, but the method has a serious weakness in that it suffers from an instability problem. The implicit integration method is a possible solution, but a critical flaw of the implicit method is that it involves a large linear system. This paper presents an approximate implicit method for the mass-spring model. The proposed technique updates with stability the state of n mass points in O(n) time when the number of total springs is O(n). In order to increase the efficiency of simulation or reduce the numerical errors of the proposed approximate implicit method, the number of mass points must be as small as possible. However, coarse discretization with a small number of mass points generates an unrealistic appearance for a cloth model. By introducing a wrinkled cubic spline curve, we propose a new technique that generates realistic details of the cloth model, even though a small number of mass points are used for simulation.     

A standard model for multimedia synchronization: PREMO synchronization objects

This paper describes an event-based synchronization mechanism, which is at the core of the inter-media synchronization in the upcoming standard for multimedia presentation, PREMO. The synchronization mechanism of PREMO is a powerful tool, based on a small number of concepts, and on cooperation among active objects, and represents a synthesis of various synchronization models described in the literature. This model can serve as a basis for the implementation of complex synchronization patterns in multimedia presentations, both purely event-based, as well as time-based.     

Efficient collision detection for models deformed by morphing

Published online: 5 February 2003     

Using extended feature objects for partial similarity retrieval

In this paper, we introduce the concept of extended feature objects for similarity retrieval. Conventional approaches for similarity search in databases map each object in the database to a point in some high-dimensional feature space and define similarity as some distance measure in this space. For many similarity search problems, this feature-based approach is not sufficient. When retrieving partially similar polygons, for example, the search cannot be restricted to edge sequences, since similar polygon sections may start and end anywhere on the edges of the polygons. In general, inherently continuous problems such as the partial similarity search cannot be solved by using point objects in feature space. In our solution, we therefore introduce extended feature objects consisting of an infinite set of feature points. For an efficient storage and retrieval of the extended feature objects, we determine the minimal bounding boxes of the feature objects in multidimensional space and store these boxes using a spatial access structure. In our concrete polygon problem, sets of polygon sections are mapped to 2D feature objects in high-dimensional space which are then approximated by minimal bounding boxes and stored in an R-tree. The selectivity of the index is improved by using an adaptive decomposition of very large feature objects and a dynamic joining of small feature objects. For the polygon problem, translation, rotation, and scaling invariance is achieved by using the Fourier-transformed curvature of the normalized polygon sections. In contrast to vertex-based algorithms, our algorithm guarantees that no false dismissals may occur and additionally provides fast search times for realistic database sizes. We evaluate our method using real polygon data of a supplier for the car manufacturing industry. Edited by R. Güting. Received October 7, 1996 / Accepted March 28, 1997     

Automated generation of control skeletons for use in animation

Published online: 15 March 2002     

Parametric G n blending of curves and surfaces

We introduce a simple blending method for parametric curves and surfaces that produces families of parametrically defined, G ⁿ –continuous blending curves and surfaces. The method depends essentially on the parameterizations of the curves/surfaces to be blended. Hence, the flexibility of the method relies on the existence of suitable parameter transformations of the given curves/surfaces. The feasibility of the blending method is shown by several examples. The shape of the blend curve/surface can be changed in a predictable way with the aid of two design parameters (thumb weight and balance).     

Analog computation for phase-based disparity estimation: continuous and discrete models

The analog implementation of a phase-based technique for disparity estimation is discussed. This technique is based on the convolution of images with Gabor filters. The article shows that by replacing the Gaussian envelope with other envelopes, the convolution operation is equivalent to the solution of a system of differential equations, whose order is related to the smoothness of the kernel. A detailed comparison between the disparity estimates obtained using these kernels and those obtained using the standard filter is presented. The discretization of the model leads to lattice networks in which the number of connections per node required to perform convolution is limited to the first few nearest neighbors. The short connection length makes these filter suitable for analog VLSI implementation, for which the number of connection per node is a crucial factor. Experimental measures on a prototype CMOS 17-node chip validated the approach. Received: 27 October 1997 / Accepted: 18 June 1998     

Multimouth surfaces for synthetic actor animation

Most parts of the human body are cylindrical in shape. Generalized cylinders, with two cross-sectional openings, are a logical choice to represent these cylindrical shapes. However, a variety of human body regions can be visualized as surfaces with multiple openings or multimouth (MM) surfaces. Some examples of such surfaces are the pelvis, the chest, and the palms of the hands. We investigated the suitability of non-uniform rational B-spline (NURBS) formulation for creating multimouth surfaces. Two techniques, the surface wrapping model and the garland model, are presented.     

Interactive animation of parametric models

This paper describes a program which allows parametric models of three-dimensional characters and scenes to be interactively controlled for computer animation. The system attempts to span the two most common approaches to animation: language-driven or programmed and visually-driven or interactive. Models are designed in a geometry language which supports vector and matrix arithmetic, transformations and instancing of primitive parts. As a result, constraints and functional dependencies between different parts can be programmed. Control is achieved by parameterizing the model. Subsets of parameters can be connected to different logical input devices, establishing an input mode to control the model's shape. Parameter sets can be stored to form a database of positions. Positions then can be mapped to frames and interpolated to animate the model.     

The reconstruction of dynamic 3D structure of biological objects using stereo microscope images

In this paper, we address the analysis of 3D shape and shape change in non-rigid biological objects imaged via a stereo light microscope. We propose an integrated approach for the reconstruction of 3D structure and the motion analysis for images in which only a few informative features are available. The key components of this framework are: 1) image registration using a correlation-based approach, 2) region-of-interest extraction using motion-based segmentation, and 3) stereo and motion analysis using a cooperative spatial and temporal matching process. We describe these three stages of processing and illustrate the efficacy of the proposed approach using real images of a live frog's ventricle. The reconstructed dynamic 3D structure of the ventricle is demonstrated in our experimental results, and it agrees qualitatively with the observed images of the ventricle.