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At least 829 records · Page 46Linked to original sources
PubMed2004

Arbitrary viewpoint video synthesis from multiple uncalibrated cameras.

We propose a method for arbitrary view synthesis from uncalibrated multiple camera system, targeting large spaces such as soccer stadiums. In Projective Grid Space (PGS), which is a three-dimensional space defined by epipolar geometry between two basis cameras in the camera system, we reconstruct three-dimensional shape models from silhouette images. Using the three-dimensional shape models reconstructed in the PGS, we obtain a dense map of the point correspondence between reference images. The obtained correspondence can synthesize the image of arbitrary view between the reference images. We also propose a method for merging the synthesized images with the virtual background scene in the PGS. We apply the proposed methods to image sequences taken by a multiple camera system, which installed in a large concert hall. The synthesized image sequences of virtual camera have enough quality to demonstrate effectiveness of the proposed method.

Algorithms↗
PubMed2004

On combining support vector machines and simulated annealing in stereovision matching.

This paper outlines a method for solving the stereovision matching problem using edge segments as the primitives. In stereovision matching, the following constraints are commonly used: epipolar, similarity, smoothness, ordering, and uniqueness. We propose a new strategy in which such constraints are sequentially combined. The goal is to achieve high performance in terms of correct matches by combining several strategies. The contributions of this paper are reflected in the development of a similarity measure through a support vector machines classification approach; the transformation of the smoothness, ordering and epipolar constraints into the form of an energy function, through an optimization simulated annealing approach, whose minimum value corresponds to a good matching solution and by introducing specific conditions to overcome the violation of the smoothness and ordering constraints. The performance of the proposed method is illustrated by comparative analysis against some recent global matching methods.

Algorithms↗
PubMed2004

A subsumptive, hierarchical, and distributed vision-based architecture for smart robotics.

We present a distributed vision-based architecture for smart robotics that is composed of multiple control loops, each with a specialized level of competence. Our architecture is subsumptive and hierarchical, in the sense that each control loop can add to the competence level of the loops below, and in the sense that the loops can present a coarse-to-fine gradation with respect to vision sensing. At the coarsest level, the processing of sensory information enables a robot to become aware of the approximate location of an object in its field of view. On the other hand, at the finest end, the processing of stereo information enables a robot to determine more precisely the position and orientation of an object in the coordinate frame of the robot. The processing in each module of the control loops is completely independent and it can be performed at its own rate. A control Arbitrator ranks the results of each loop according to certain confidence indices, which are derived solely from the sensory information. This architecture has clear advantages regarding overall performance of the system, which is not affected by the "slowest link," and regarding fault tolerance, since faults in one module does not affect the other modules. At this time we are able to demonstrate the utility of the architecture for stereoscopic visual servoing. The architecture has also been applied to mobile robot navigation and can easily be extended to tasks such as "assembly-on-the-fly."

Algorithms↗
PubMed2004

Efficient generation of discontinuity-preserving adaptive triangulations from range images.

This paper presents an efficient technique for generating adaptive triangular meshes from range images. The algorithm consists of two stages. First, a user-defined number of points is adaptively sampled from the given range image. Those points are chosen by taking into account the surface shapes represented in the range image in such a way that points tend to group in areas of high curvature and to disperse in low-variation regions. This selection process is done through a noniterative, inherently parallel algorithm in order to gain efficiency. Once the image has been subsampled, the second stage applies a two and one half-dimensional Delaunay triangulation to obtain an initial triangular mesh. To favor the preservation of surface and orientation discontinuities (jump and crease edges) present in the original range image, the aforementioned triangular mesh is iteratively modified by applying an efficient edge flipping technique. Results with real range images show accurate triangular approximations of the given range images with low processing times.

Algorithms↗
PubMed2006

Recursive camera-motion estimation with the trifocal tensor.

In this paper, an innovative extended Kalman filter (EKF) algorithm for pose tracking using the trifocal tensor is proposed. In the EKF, a constant-velocity motion model is used as the dynamic system, and the trifocal-tensor constraint is incorporated into the measurement model. The proposed method has the advantages of those structure- and-motion-based approaches in that the pose sequence can be computed with no prior information on the scene structure. It also has the strengths of those model-based algorithms in which no updating of the three-dimensional (3-D) structure is necessary in the computation. This results in a stable, accurate, and efficient algorithm. Experimental results show that the proposed approach outperformed other existing EKFs that tackle the same problem. An extension to the pose-tracking algorithm has been made to demonstrate the application of the trifocal constraint to fast recursive 3-D structure recovery.

Algorithms↗
PubMed2006

New pose-detection method for self-calibrated cameras based on parallel lines and its application in visual control system.

In this paper, a new method is proposed to detect the pose of an object with two cameras. First, the intrinsic parameters of the cameras are self-calibrated with two pairs of parallel lines that are orthogonal. Then, the poses of the cameras relative to the parallel lines are deduced, and the rotational transformation between the two cameras is calculated. With the intrinsic parameters and the relative pose of the two cameras, a method is proposed to obtain the poses of a line, plane, and rigid object. Furthermore, a new visual-control method is developed using a pose detection rather than a three-dimensional reconstruction. Experiments are conducted to verify the effectiveness of the proposed method.

Algorithms↗
PubMedDate not supplied

Interactive stereoscopic rendering of volumetric environments.

We present an efficient stereoscopic rendering algorithm supporting interactive navigation through large-scale 3D voxel-based environments. In this algorithm, most of the pixel values of the right image are derived from the left image by a fast 3D warping based on a specific stereoscopic projection geometry. An accelerated volumetric ray casting then fills the remaining gaps in the warped right image. Our algorithm has been parallelized on a multiprocessor by employing effective task partitioning schemes and achieved a high cache coherency and load balancing. We also extend our stereoscopic rendering to include view-dependent shading and transparency effects. We have applied our algorithm in two virtual navigation systems, flythrough over terrain and virtual colonoscopy, and reached interactive stereoscopic rendering rates of more than 10 frames per second on a 16-processor SGI Challenge.

Algorithms↗
PubMedDate not supplied

Incremental penetration depth estimation between convex polytopes using dual-space expansion.

We present a fast algorithm to estimate the penetration depth between convex polytopes in 3D. The algorithm incrementally seeks a "locally optimal solution" by walking on the surface of the Minkowski sums. The surface of the Minkowski sums is computed implicitly by constructing a local dual mapping on the Gauss map. We also present three heuristic techniques that are used to estimate the initial features used by the walking algorithm. We have implemented the algorithm and compared its performance with earlier approaches. In our experiments, the algorithm is able to estimate the penetration depth in about a milli-second on an 1 GHz Pentium PC. Moreover, its performance is almost independent of model complexity in environments with high coherence between successive instances.

Algorithms↗
PubMedDate not supplied

TORNADO: omnistereo video imaging with rotating optics.

One of the key techniques for vision-based communication is omnidirectional stereo (omnistereo) imaging, in which stereoscopic images for an arbitrary horizontal direction are captured and presented according to the viewing direction of the observer. Although omnistereo models have been surveyed in several studies, few omnistereo sensors have actually been implemented. In this paper, a practical method for capturing omnistereo video sequences using rotating optics is proposed and evaluated. The rotating optics system consists of prism sheets, circular or linear polarizing films, and a hyperboloidal mirror. This system has two different modes of operation with regard to the separation of images for the left and right eyes. In the high-speed shutter mode, images are separated using postimage processing, while, in the low-speed shutter mode, the image separation is completed by optics. By capturing actual images, we confirmed the effectiveness of the methods.

Computer Simulation↗
PubMedDate not supplied

Correcting interperspective aliasing in autostereoscopic displays.

An image presented on an autostereoscopic system should not contain discontinuities between adjacent views. A viewer should experience a continuous scene when moving from one view to the next. If corresponding points in two perspectives do not spatially abut, a viewer will experience jumps in the scene. This is known as interperspective aliasing. Interperspective aliasing is caused by object features far away from the stereoscopic screen being too small, which results in visual artifacts. By modeling a 3D point as a defocused image point, we can adapt Fourier analysis to devise a depth-dependent filter kernel that allows filtering of a stereoscopic 3D image. For synthetic 3D data, we use a simpler approach, which is to smear the data by a distance proportional to its depth.

Algorithms↗
PubMedDate not supplied

Scanning scene tunnel for city traversing.

This paper proposes a visual representation named scene tunnel for capturing urban scenes along routes and visualizing them on the Internet. We scan scenes with multiple cameras or a fish-eye camera on a moving vehicle, which generates a real scene archive along streets that is more complete than previously proposed route panoramas. Using a translating spherical eye, properly set planes of scanning, and unique parallel-central projection, we explore the image acquisition of the scene tunnel from camera selection and alignment, slit calculation, scene scanning, to image integration. The scene tunnels cover high buildings, ground, and various viewing directions and have uniformed resolutions along the street. The sequentially organized scene tunnel benefits texture mapping onto the urban models. We analyze the shape characteristics in the scene tunnels for designing visualization algorithms. After combining this with a global panorama and forward image caps, the capped scene tunnels can provide continuous views directly for virtual or real navigation in a city. We render scene tunnel dynamically by view warping, fast transmission, and flexible interaction. The compact and continuous scene tunnel facilitates model construction, data streaming, and seamless route traversing on the Internet and mobile devices.

Algorithms↗
PubMed2004

The role of misorientation and phosphorus content on grain growth and intergranular fracture in iron-carbon-phosphorus alloys.

The relationship between the crystallography of intergranular fracture and phosphorus segregation has been investigated in a Fe-0.06wt%P-0.002wt%C alloy aged for 1 h at temperatures between 600 degrees C and 1000 degrees C. Two novel techniques were devised for the investigation: first, electron back-scatter diffraction (EBSD) across the reconstructed fracture surface and, second, a combination of Auger electron spectroscopy, stereophotogrammetry and microscopy to measure phosphorus and carbon on fracture facets combined with EBSD measurements direct from the fracture surface. In total, 700 misorientations were measured from across the reconstructed fracture surface and in 'control' areas away from the fracture. It was found that Sigma 3s were in general more resistant to brittle fracture than were random boundaries, and it was suggested that alloys of this type could be grain boundary engineered to improve fracture resistance by a short anneal in the austenite region to increase the final proportion of Sigma 3s. Sixteen fracture facets yielded combined Auger/EBSD data. The combined Auger/EBSD methodology to acquire joint crystallographic and segregation information from facets was shown to be feasible, although laborious. There were significantly more [110] planes than any other type in the sample population of facets from which combined segregation/crystallography data had been collected. The data suggested that there was on average lower phosphorus segregation on fracture facets that were near [110] than on other intergranular fracture facets.

Alloys↗
PubMed2004

Quantitative evaluation of severity in psoriatic lesions using three-dimensional morphometry.

The severity of psoriasis has been traditionally assessed by measures, such as the psoriasis area and severity index (PASI), the psoriasis severity scores, and the lesional severity scores. As a result, even experienced dermatologists show variations when attempting to determine the severity of psoriasis. Therefore, a better non-invasive and objective measurement of clinical signs is needed. In this study, an instrument, a so-called 'stereoimage optical topometer' (SOT), based on a new concept of 'stereoimaging' was used to measure the three-dimensional skin surface. The aim of this study was to compare the results obtained by the SOT with the visual score of psoriasis lesion. Thirty psoriatic patients were enrolled in this study. Initially, the severity of the infiltration and the scale of 134 psoriatic lesions were assessed by using a visual scoring system (0: none, 1: mild, 2: moderate, 3: severe, and 4: very severe), as scored by five dermatologists. The SOT was then used to quantify the severity of each psoriatic lesion using four three-dimensional SOT parameters (Sa, SL, SA, and SV). Secondly, the involved skin-surface area in the psoriasis cases was scored by the naked eye by the five dermatologists and by image analysis. Statistically significant differences were observed between grades 0, 1, 2, and 3 in terms of the severity measurements of the individual psoriatic lesions by SOT when using the parameters Sa, SL, SA, and SV. Therefore, it was concluded that there is a strong correlation between the results measured by visual scoring and by SOT in psoriasis.

Adult↗
PubMed1979

Evaluation of leg ulcer treatment with stereophotogrammetry. A pilot study.

This report describes stereophotogrammetric measurements of leg ulcers. A basic technical description of the method and its application in a pilot study are presented. The clinical evaluation of the healing of leg ulcers is compared to the photogrammetrically determined parameters--edge length, surface area, and volume--of the ulcers, and seems to fulfil the need for an objective method in the evaluation of leg ulcer treatment.

Aged↗
PubMed1979

Quantitative analysis of histological parameters in giant cell lesions of the jaws and long bones.

Stereological techniques have been used to compare histological parameters of the giant cell component in 10 giant cell tumours of long bones, 10 central giant cell granulomas of the jaws and 10 peripheral giant cell granulomas of the jaws. The giant cell parameters investigated were: mean profile diameter, mean diameter, mean profile axial ratio, volume-to-surface ratios, nuclear numerical density, profile area and cell volume. Serial sections were cut at 4 micron from routinely fixed, paraffin-embedded specimens of each case and two sections, separated by 100 micron, were stained with haematoxylin and eosin. Random fields were photographed until at least 25 giant cell profiles had been recorded from each of the two sections of each lesion. The processed film was projected for point and intersect counting, the entire procedure ensuring double-blind assessment of the cases under investigation. In general there was no significant difference for any of the parameters between the giant cells of central and peripheral jaw lesions. There was a significant difference, however, between the giant cells of central jaw lesions and long bone tumours in respect of both nuclear numerical density and mean absolute cell volume.

Adolescent↗
PubMed1976

Stereo photomicrography of Golgi preparations.

Photomicrographs of thick sections taken with reciprocal, lateral illumination in a compound microscope produce stereo-pairs. The method is particularly useful with thick celloidin sections of nervous tissue impregnated with the Golgi selective silver technique.

Animals↗
PubMed1981

Photoelectron microscopy of cell surface topography.

Photoelectron micrographs of gold-palladium coated mouse 3T3 cells and chick embryo fibroblasts are presented. Since the gold-palladium suppresses differences in work function, the cell morphology seen in these micrographs is due to relief contrast. The heights of comparable cells were measured from the parallax present in transmission electron micrograph stereo-pairs of cell surface replicas. The origin of relief contrast and the effect of cell surface relief on the working depth of field in photoelectron images of cells are discussed. The micrographs demonstrate that photoelectron microscopy is very sensitive to fine details of cell surface topography, and that the working depth of field is not a limiting factor in the imaging of well-spread tissue culture cells.

Animals↗