Showing papers in "The Visual Computer in 1990"

A global human walking model with real-time kinematic personification

Abstract: Presents a human walking model built from experimental data based on a wide range of normalized velocities. The model is structured on two levels. On the first level, global spatial and temporal characteristics are generated. On the second level, a set of parameterized trajectories produce both the position of the body in space and the internal body configuration. This is performed for a standard structure and an average configuration of the human body. The experimental context corresponding to the model is extended by allowing a continuous variation of global spatial and temporal parameters according to the motion rendition expected by the animator. The model is based on a simple kinematic approach designed to keep the intrinsic dynamic characteristics of the experimental model. Such an approach also allows a personification of the walking action in an interactive real-time context in most cases. A correction automata of such motion is then proposed

Heuristics for ray tracing using space subdivision

Abstract: Ray tracing requires testing of many rays to determine intersections with objects. A way of reducing the computation is to organize objects into hierarchical data structures. We examine two heuristics for space subdivisions using bintrees, one based on the intuition that surface area is a good estimate of intersection probability, one based on the fact that the optimal splitting plane lies between the spatial median and the object median planes of a volume. Traversal algorithms using cross links between nodes are presented as generalizations of ropes in octrees. Simulations of the surface area heuristic and the cross link scheme are presented. These results generalize to other hierarchical data structures.

Volume rendering by adaptive refinement

Abstract: Volume rendering is a technique for visualizing sampled scalar functions of three spatial dimensions by computing 2D projections of a colored semi-transparent gel. This paper presents a volume-rendering algorithm, in which image quality is adaptively refined over time. An initial image is generated by casting a small number of rays into the data, less than one ray per pixel, and interpolating between the resulting colors. Subsequent images are generated by alternately casting more rays and interpolating. The usefulness of these rays is maximized by distributing them according to measures of local image complexity. Examples from two applications are given: molecular graphics and medical imaging.

3D visualization of tomographic volume data using the generalized voxel model

Abstract: Multi-slice images obtained from computer tomography and magnetic resonance imaging represent a 3D image volume. For its visualization we use a raycasting algorithm working on a gray-scale voxel data model. This model is extended by additional attributes such as membership to an organ or a second imaging modality (“generalized voxel model”). It is shown that the combination of different surface-rendering algorithms together with cutting and transparent display allow a realistic visualization of the human anatomy.

Interactive garment design

Abstract: A method for the design of garments at a workstation is proposed. An underlying body form analogous to a trade mannequin is first represented in the computer. Garment panels are considered to be surfaces of complex shape, whose fit with respect to body form may vary over the surface. A method of easy entry of data for representing panels is proposed, whereby fit around panel edges can be defined. The problems of controlling fit in the interior of panels is considered and a scheme is proposed which accomplishes design with economy of effort from the designer.

Using hand position for virtual object placement

Abstract: Placement of an object in three-dimensional space is a six-degree-of-freedom (6D) operation requiring three variables to specify location and three more to specify orientation. This paper reports on an investigation using a six-degree-of-freedom digitizer to manipulate 3D scenes stored in a computer. Two experiments are presented, which evaluate speed and accuracy of placement under different conditions. Results show that placement times are faster with stereopsis, when z translations are disabled (when accurate translation is required) and when both rotations and translations are allowed simultaneously. The implications of these results are discussed.

Singularity theoretical modeling and animation of garment wrinkle formation processes

Abstract: To understand the nature of garments as worn, it is essential to model and animate the formation process of garment wrinkles. Because the number of components making up a garment is extremely high, simulating its behavior under dynamic constraints requires a very large amount of computation, and the result is difficult to analyze and understand. We show that exploiting geometric features of wrinkles can greatly increase the understandability of the computed result, while not much increasing the amount of computation needed. We present the modeling primitives of garment wrinkles, which can suitably represent geometric features of wrinkles under the dynamic constraints. Extracting geometric features based on singularity theory enables us to model the qualitative shape change of wrinkles. The formation process of wrinkles is animated by using these primitives.

Facial image synthesis using skin texture recording

Abstract: A significant issue in synthesizing realistic faces is the representation of skin grain and wrinkles. This paper describes a new approach based on the registered body of a real person. This recording allows simultaneously registering of the 3-D coordinates of a point and the corresponding reflected intensity. Using a 4-D B-spline surface to reconstruct the face, we come close to achieving a photographic result.

A highly flexible multiprocessor solution for ray tracing

Abstract: The ray tracing algorithm continues to attract much research and development to improve the quality of the images that are generated, and to reduce the time taken to produce them. By identifying the key requirements of a development system from the user's point of view, we describe a general-purpose multiprocessor solution for ray tracing which may be used to reduce execution time without restricting development of the ray tracing code. The solution is based upon a distributed memory multiprocessor system in which each processor addresses a small amount of memory relative to the size of the model database. Methods for exploiting the coherence of references to entries in the database are described which use a combination of dynamic and static caching techniques. This scheme allows databases of arbitrary size to be supported on multiprocessors with limited distributed memory.

Real time discrete shading

Abstract: A shading technique for voxel-based images, termedcongradient shading, is presented. As the surface information is not available in voxel representation, the surface normal must be recovered from the 3D discrete voxel map itself. The technique defines the normal as one of a finite set of neighborhood-estimated gradients and can thus employ precalculated look-up tables. Furthermore, a table-driven mechanism permits changing the light source parameters by merely redefining the look-up table. The technique uses only simple arithmetic operations and is thus suitable for hardware implementation. Since it has been implemented not as a post-processor, but as part of the projection pipeline of the cube architecture, congradient shading can be executed in real time. Two versions of the technique in real time. Two versions of the technique have been conceived and implemented:unidirectional shading, in which the gradient is estimated only from neighborhoods along the scan-lines;bidirectional shading, in which both horizontal and vertical components of the gradient are considered. In spite of the simplicity of the technique, the results are practically indistinguishable from images generated by conventional techniques.

Improved techniques for ray tracing parametric surfaces

Abstract: Several techniques for acceleration of ray tracing parametric surfaces are presented. Some of these are entirely new to ray tracing, while others are improvements of previously known techniques. First a uniform spatial subdivision scheme is adapted to parametric surfaces. A new space- and time-efficient algorithm for finding raysurface intersections is introduced. It combines numerical and subdivision techniques, thus allowing utilization of ray coherence and greatly reducing the average ray-surface intersection time. Non-scanline sampling orders of the image plane are proposed that facilitate utilization of coherence. Finally, a method to handle reflected, refracted, and shadow rays in a more efficient manner is described. Results of timing tests indicating the efficiency of these techniques for various environments are presented.

Ray tracing voxel data via biquadratic local surface interpolation

Abstract: Various shaded hidden-surface display techniques have been used to render voxel data. In this paper, an approach to using general ray tracing for the rendering of voxel data is presented. Central to this approach is the interpolation of a surface with respect to the volume of a given voxel and its neighbors. Nine columns (of three voxel volumes each) provide sufficient constraints on the integral of a biquadratic function over the column's base to solve its specific coefficients. The use of these locally interpolated surfaces to define a scene to be ray traced is investigated.

An object-oriented architecture for a computer animation system

Abstract: This paper describes the architecture, capabilities and implementation of The Clockworks, an object-oriented computer animation system encompassing a wide variety of modeling, image synthesis, animation, programming and simulation capabilities in a single integrated environment. The object-oriented features of The Clockworks are implemented in portable C under UNIX using a programming discipline. These features include objects with methods and instance variables, class hierarchies, inheritance, instantiation and message passing.

Directing an animated scene with autonomous actors

Abstract: The main advantage in using motion recording systems for human figure animation is that exact replication of real movements can be achieved. In this paper, we present Pinocchio, an animation system that allows the control of human motion by introducing facilities for the design of animation sequences. In Pinocchio, movements performed by real actors are digitized using Elite, a 3D vision system based on a two-level architecture reflecting the hierarchical structure of vision in living beings. A general movement dictionary has been developed to classify movements and each movement in the dictionary has been stored in a motion database where it is available for display. Sequences of movements of the characters acting in an animated scene are specified by the animator through an animation script, then before display the characters themselves take care of the coordination issues related to the scene.

Ray-bound tracing for perfect and efficient anti-aliasing

Abstract: A complete detection of whether aliasing occurs in a given pixel is possible by using the concept of bounded rays and raybound tracing. A coherent set of rays can be bounded by bounding both their origins (by a sphere) and directions (by a circle on a unit sphere). By tracing bounds of rays in a pixel, along the direction of reflection, refraction or to light sources, it is possible to obtain an upper bound on the degree of aliasing in the pixel. Ray bound tracing is possible against various shapes and with various shading algorithms.

Evaluation of true 3D display systems for visualizing medical volume data

Abstract: The last few years have witnessed extraordinary advances in medical imaging. The new digital methods, such as CT or MRI, share the common characteristic of providing three-dimensional volume data. The urgent need for efficient techniques for visualizing volume data has recently been recognized not only in diagnostic medicine, but also in computer-assisted surgery and radiation-therapy planning. In recent years, new display technologies have emerged, in which depth perception has been improved significantly, because it relies in principle on physiological depth cues. This paper presents the state-of-theart is true 3D displays (with a special emphasis placed on equipment that has reached relative maturity) and a discussion of their most important advantages and disadvantages with respect to visualizing medical data.

Graph-directed modelling from serial sections

Abstract: We propose a general 3D-surface reconstruction technique for objects defined in terms of contours in a stack of serial sections. It is built around a data structure, in which the topology of the objects is represented as a set of disconnected graphs. The basic idea is to let the topological information direct the reconstruction process. There are several advantages with this approach. The alignment of the stack of sections is computed automatically. This operation does not depend on artificial reference points, such as fiduciary marks introduced by laser-beam penetration of a biological sample prior to sectioning. Furthermore, the unknown surfaces between successive sections can be created automatically, even though the sections contain a large number of arbitrarily shaped contours that are clustered or perhaps partly overlapped. If present, 3D irregularities in the surface model can be reduced in a controlled manner.

A technique for motion specification in computer animation

Abstract: A technique is discussed for the interactive specification and real-time evaluation of the movements of geometrical objects with several degrees of freedom. The technique is a midway between a faithful simulation of the dynamics and kinematics of the object and completely free user control, and as such it is well suited for animated drawings, for example. The method works in two steps: first, the motion of a relevant subobject (the skeleton) is specified interactively in real time. Next, the entire object is deformed and oriented in space such as to match the form of the skeleton. Depending on the complexity of the object, this second step either takes place in real time, or as a batch process. Several forms of geometrical constraints, as well as stretching and squeezing, are supported.

Adaptive polygonization of parametric surfaces

Abstract: This paper describes an algorithm for dividing a (u, v)-parametric surface into the least possible number of plane triangular elements that closely follow the surface they approximate. The concept, of closeness defined here is based on a set of three subdivision criteria: unit-normal criterion, chord-distance criterion, and edge-refinement criterion.

Two data structures for building tetrahedralizations

Abstract: A polyhedral decomposition can be unambiguously described as the collection of four primitive elements (i.e., polyhedra, facets, edges, and vertices) plus their mutual adjacency relations. We consider here the problem of representing a specific kind of polyhedral decomposition, i.e., a tetrahedralization. We describe two different representations for a tetrahedralization. The first one can only model polyhedral decompositions with tetrahedral cells, while the second one is suitable for describing any partition of a volume into polyhedral cells with triangular facets. We present two sets of primitive Euler operators, which build and manipulate such representations while maintaining their topological integrity. The use of such operators is demonstrated in connection with two algorithms for building a Delaunay tetrahedralization, which show the different hedralization, which show the different uses of the two representations.

Who invented ray tracing

Abstract: We provide some remarks on the very early developments of the visualization techniques conducted during the European Renaissance It is shown that the basic principle of ray tracing was already presented by Albrecht Durer (1471–1528) in 1525 This article is intended to be of common interest; it is not a scientific report

Polygon-based post-process motion blur

Abstract: This paper discusses a three-pass raster motion-blur algorithm (and some generalizations) in the context of texture-mapped polygons and its application to blurring objects and surfaces made up of multiple polygons, which may move in different directions.

Approximating CSG trees of moving objects

Abstract: A discussion of the relationship between two solid representation schemes is presented: CSG trees and recursive spatial subdivision exemplified by the bintree, a generalization of the quadtree and octree. Detailed algorithms are developed and analyzed for evaluating CSG trees by bintree conversion. These techniques are shown to enable the addition of the time dimension and motion to the approximate analysis of CSG trees. This facilitates the solution of problems such as static and dynamic interference detection. A technique for projecting across any dimension is also shown. For “well-behaved” CSG trees the execution time of the conversion algorithm is directly related to the spatial complexity of the object represented by the CSG tree (i.e., as the resolution increases, it is asymptotically proportional to the number of bintree nodes and does not depend on the size or form of the CSG tree representation). The set of well-behaved CSG trees include all trees that define multidimensional polyhedra in a manner that does not give rise to tangential intersections at CSG tree nodes.

Vu: visual user-interface design

Abstract: Vu is an interactive visual programming environment, which enables interface designers to create highly interactive, graphical, direct-manipulation-style graphical user interfaces in a very natural manner The general strategy of vu is to enable the designer to draw the screen display that the end user will see, and to test the interface by performing actions just as the end user would This is achieved by providing exploratory programming in a highly visual and object-oriented environment This paper describes the design principles and structure of vu

Computer image generation for flight simulators" the Gabor approach

Abstract: A formalism for image representation in the combined frequency-position space is presented using the generalized Gabor approach. This approach uses elementary functions to which the human visual system is particularly sensitive and which are efficient for the analysis and synthesis of visual imagery. The formalism is also compatible with the implementation of a variable resolution system wherein image information is nonuniformly distributed across the visual field in accordance with the human visual system's ability to process it. When used with a gaze-slaved visual display system, imagery generated using the techniques described here affords a combination of high resolution and wide field-of-view. This combination is particularly important in high-fidelity, computergenerated, visual environments as required, for instance, in flight simulators.

Efficient traversal of well-behaved hierarchical trees of extents for ray-tracing complex scenes

Abstract: Traversal of hierarchial trees of extents (HTE) requires computation of intersections between rays and bounding volumes whose faces are parallel to the cartesian axes. By redefining the HTE so that nonoverlapping bounding volumes are generated, a well-behaved data structure is obtained in which “geometrical coherence” is applied to speed up its traversal. We distinguish two types of bounding volumes: internal boxes contain the ray's origin whileexternal bounding volumes do not contain the ray's origin. To traverse the HTE, we look first to polygons in the internal bounding volumes and deal with external boxes only when no ray-polygon intersection is found in internal nodes. As external nodes in the HTE define pruned subtrees of external bounding volumes, geometrical characteristics of the boxes are exploited for HTE traversal. A coding scheme allows a 6-bit code to determine which faces of a bounding volume need to be tested for intersection. Also, our well-behaved HTE allows for reuse of intersection points at lower levels of the tree.

Scaling low-resolution bitmap fonts using linear feature extraction

Abstract: In certain cases a font, as defined by a set of small raster images, can be scaled by first extracting the linear features that define each character. These can be treated as graphical vectors and scaled, translated, and rotated in an arbitrary fashion. The visual precision of this method depends on the size of the original front templates.

Low-cost hardware platform for developing realtime 3D graphics

Abstract: BRAD3D, a low-cost hardware platform for the development of a realtime 3D graphics software is presented. The BRAD3D configuration is derived from a generalization of 3D image synthesis. Three basic processes have been identified: the geometric process, dealing with the measurements of the scene; the topologic process, extracting visible information from the polygonal structure; and the scan-conversion process, producing pixel values on a frame buffer. BRAD3D is implemented as a three-stage pipeline and accommodates depth-list and scan-line hidden-surface-removal algorithms. Each stage of the pipeline can be implemented using different hardware solutions. A microprocessor-based solution is presented as a general prototyping approach.

Improving computer interfaces by animation from videodisc

Abstract: The experiments described in this paper aim at expanding computer interfaces by an audio-visual dimension: an animated display of a human speaker synchronized with synthesized message. The basic elements of the approach are a sophisticated text-to-speech synthesizer and a videodisc with instant jump capability. They are controlled by a specially programmed synchronizing microcomputer. This system works nearly in real time. Two series of animation experiments were carried out: (a) animation by means of instant jumps to frames corresponding to individual phonemes in the pronounced text, and (b) animation of audio and video segments by means of elastic stretching and compression in time. The quality of the results can be improved, but it is acceptable for many interface applications, such as in tutoring systems.

A note on inverted Mandelbrot sets

Abstract: A simple technique is described for demonstrating artistically interesting behavior in chaotic systems defined by complex dynamics. In particular, the Mandelbrot set for the iterative process\(\zeta \to \zeta ^p + (1/u)^p \) is explored.