An object model for computer graphics applications should contain two aspects of information: shape and reflectance properties of the object. A number of techniques have been developed for modeling object shapes by observing real objects. In contrast, attempts to model reflectance properties of real objects have been rather limited. In most cases, modeled reflectance properties are too simple or too complicated to be used for synthesizing realistic images of the object. In this paper, we propose a new method for modeling object reflectance properties, as well as object shapes, by observing real objects. First, an object surface shape is reconstructed by merging multiple range images of the object. By using the reconstructed object shape and a sequence of color images of the object, parameters of a reflection model are estimated in a robust manner. The key point of the proposed method is that, first, the diffuse and specular reflection components are separated from the color image sequence, and then, reflectance parameters of each reflection component are estimated separately. This approach enables estimation of reflectance properties of real objects whose surfaces show specularity as well as diffusely reflected lights. The recovered object shape and reflectance properties are then used for synthesizing object images with realistic shading effects under arbitrary illumination conditions.

A simple, fast, and approximate voxel-based approach to 6-DOF haptic rendering is presented. It can reliably sustain a 1000 Hz haptic refresh rate without resorting to asynchronous physics and haptic rendering loops. It enables the manipulation of a modestly complex rigid object within an arbitrarily complex environment of static rigid objects. It renders a short-range force field surrounding the static objects, which repels the manipulated object and strives to maintain a voxel-scale minimum separation distance that is known to preclude exact surface interpenetration. Force discontinuities arising from the use of a simple penalty force model are mitigated by a dynamic simulation based on virtual coupling. A generalization of octree improves voxel memory efficiency. In a preliminary implementation, a commercially available 6-DOF haptic prototype device is driven at a constant 1000 Hz haptic refresh rate from one dedicated haptic processor, with a separate processor for graphics. This system yields stable and convincing force feedback for a wide range of user controlled motion inside a large, complex virtual environment, with very few surface interpenetration events. This level of performance appears suited to applications such as certain maintenance and assembly task simulations that can tolerate voxel-scale minimum separation distances.

Visualizing three-dimensional unstructured data from aerodynamics calculations is challenging because the associated meshes are typically large in size and irregular in both shape and resolution. The goal of this research is to develop a fast, efficient parallel volume rendering algorithm for massively parallel distributed-memory supercomputers consisting of a large number of very powerful processors. We use cell-projection instead of ray-casting to provide maximum flexibility in the data distribution and rendering steps. Effective static load balancing is achieved with a round robin distribution of data cells among the processors. A spatial partitioning tree is used to guide the rendering, optimize the image compositing step, and reduce memory consumption. Communication cost is reduced by buffering messages and by overlapping communication with rendering calculations as much as possible. Tests on the IBM SP2 demonstrate that these strategies provide high rendering rates and ...

An algorithm for the robust and fast automatic construction of a 3D model of any real object using images from multiple views is presented. The images are taken from a real object rotating in front of a stationary calibrated CCD TV camera. The object silhouettes extracted from the input images, the related turntable positions and camera orientation are used to construct the volume model of the real object by applying the method of occluding contours. A keypoint in performing this method is a proper volume representation, characterized by low complexity and suitability for a fast computation of volume models. In the presented approach, each volume model is described by pillar–like volume elements (pillars) ensuring a computational complexity proportional to the size of the real object surface and enabling a fast and simple construction of the volume model. The fast performance is due to the simple projection feasibility of those pillars and the easy–to–perform intersection test for the object silhouette with the projected pillars. Results with real image sequences have confirmed the robustness of the developed algorithm even for the modelling of real objects with highly detailed and complex surfaces and the use of imperfect object silhouettes. 1

This paper examines the construction of a 3-D surface model of an object rotating in front of a camera. Previous research in depth from motion has demonstrated the power of using an incremental approach to depth estimation. In this paper, we extend this approach to more general motion and use a full 3-D surface model instead of a 2 1 = 2 -D sketch. The algorithm starts with a flow field computed using local correlation. It then projects individual measurements into 3-D points with associated uncertainties. Nearby points from successive frames are merged to improve the position estimates. These points are then used to construct a finite element surface model, which is itself refined over time. We demonstrate the application of our new techniques to several real image sequences. Keywords: Computer vision, 3-D model construction, image sequence (motion) analysis, optic flow, Kalman filter, surface interpolation, computer aided design, computer graphics animation. c flDigital Equipment C...

Algorithms are presented for moving between adjacent blocks in an octree representation of an image. Motion is possible in the direction of a face, edge, and a vertex, and between blocks of arbitrary size. The algorithms are based on a generalization and simplification of techniques developed earlier for two dimensions (i.e., in quadtrees). They are also applicable to quadtrees. The difference lies in the graph-theoretical classification of adjacencies-i.e., in terms of vertices, edges, and faces. Algorithms are given for octrees that are implemented with pointers and with pointerless representations such as the linear octree. 0 1989 Academic PRSS. ITIC. 1.

This paper deals with the automation of dextrous grasping in a partly known environment using a stereo vision system and a multifingered hand mounted on a robot arm. Effective grasping requires a combination of sensing and planning capabilities: sensing to construct a well-adapted model of the situation and to guide the execution of the task, and planning to determine an appropriate grasping strategy and to generate safe, feasible manipulator motions. We propose an integrated approach that combines computer vision, path planning, and manipulator control in three complementary activities: the reconstruction of task-oriented models of the workspace, the determination of appropriate grasping configurations from computed `preshapes' of the hand, and the automatic generation and execution of hand/arm motions using a hybrid geometric path planner and a hybrid control system. This paper outlines the architecture of our system, discusses the new models and techniques we have developed, and fin...

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A number of algorithms are presented for obtaining~a~i&?ter representation for an image given its quadtree. The algorithms are given in an evolutionary manner starting with the straightforward top-down approach that visits each run in a row in succession starting at the root of the tree. The remaining algorithms proceed in a manner akin to an inorder tree traversal. All of the algorithms are analyzed and an indication is given as to when each is preferable. The execution time of all of the algorithms is shown to be proportional to the sum of the heights of the blocks comprising the image. 1.

The construction of a three-dimensional object model from a set of images taken from different viewpoints is an important problem in computer vision. One of the simplest ways to do this is to use the silhouettes of the object (the binary classification of images into object and background) to can construct a bounding volume for the object. To efficiently represent this volume, we use an octree, which represents the object as a tree of recursively subdivided cubes. We develop a new algorithm for computing the octree bounding volume from multiple silhouettes, and apply it to an object rotating on a turntable in front of a stationary camera. The algorithm performs a limited amount of processing for each viewpoint, and incrementally builds the volumetric model. The resulting algorithm requires less total computation than previous algorithms, runs in real-time, and builds a model whose resolution improves over time. Keywords: Computer vision, 3-D model construction, image sequence (motion) ...