Showing papers on "3D reconstruction published in 1994"
TL;DR: An interactive system exploits recent computer graphics and computer vision techniques to significantly reduce the time required to build 3D nerve cell models from serial microscopy.
Abstract: Neuroscientists have studied the relationship between nerve cell morphology and function for over a century. To pursue these studies, they need accurate three-dimensional models of nerve cells that facilitate detailed anatomical measurement and the identification of internal structures. Although serial transmission electron microscopy has been a source of such models since the mid 1960s, model reconstruction and analysis remain very time consuming. The authors have developed a new approach to reconstructing and visualizing 3D nerve cell models from serial microscopy. An interactive system exploits recent computer graphics and computer vision techniques to significantly reduce the time required to build such models. The key ingredients of the system are a digital "blink comparator" for section registration, "snakes," or active deformable contours, for semiautomated cell segmentation, and voxel-based techniques for 3D reconstruction and visualization of complex cell volumes with internal structures. >
124 citations
TL;DR: A three-dimensional (3D) reconstruction of the vessel lumen from two angiographic views, based on the reconstruction of a series of cross-sections, is proposed, which performs well both on single vessels and on branching vessels possessing an additional inherent ambiguity when viewed at oblique angles.
Abstract: A three-dimensional (3D) reconstruction of the vessel lumen from two angiographic views, based on the reconstruction of a series of cross-sections, is proposed Assuming uniform mixing of contrast medium and background subtraction, the cross-section of each vessel is reconstructed through a binary representation A priori information about both the slice to be reconstructed and the relationships between adjacent slices are incorporated to lessen ambiguities on the reconstruction Taking into account the knowledge of normal vessel geometry, an initial solution of each slice is created using an elliptic model-based method This initial solution is then deformed to be made consistent with projection data while being constrained into a connected realistic shape For that purpose, properties on the expected optimal solution are described through a Markov random field To find an optimal solution, a specific optimization algorithm based on simulated annealing is used The method performs well both on single vessels and on branching vessels possessing an additional inherent ambiguity when viewed at oblique angles Results on 2D slice independent reconstruction and 3D reconstruction of a stack of spatially continuous 2D slices are presented for single vessels and bifurcations >
105 citations
21 Jun 1994
TL;DR: A practical rapid algorithm for doing projective reconstruction of a scene consisting of a set of lines seen in three or more images with uncalibrated cameras, which can be applied to images from different cameras or the same camera.
Abstract: The paper gives a practical rapid algorithm for doing projective reconstruction of a scene consisting of a set of lines seen in three or more images with uncalibrated cameras. The algorithm is evaluated on real and ideal data to determine its performance in the presence of varying degrees of noise. By carefully consideration of sources of error, it is possible to get accurate reconstruction with realistic levels of noise. The algorithm can be applied to images from different cameras or the same camera. For images with the same camera with unknown calibration, it is possible to do a complete Euclidean reconstruction of the image. This extends to the case of uncalibrated cameras previous results on scene reconstruction from lines,. >
101 citations
IBM1
TL;DR: The author's computational scheme avoids point/line correspondence and is based on hierarchical estimation and image warping working directly with spatio-temporal image intensities, demonstrating how this analysis simplifies ego and multiple motion analysis, and stable scene-centered 3D reconstruction.
Abstract: Robust 3D motion and structure computation and segmentation has been the subject of an enormous body of work in reconstructive vision. For linear approximations to perspective projection (weak/para perspective), and for the case of image velocities, elegant linear methods have been devised for robust estimation. For reconstruction under arbitrary view transformations, linear projective methods using point correspondences have been suggested. In this paper, the authors present a formulation for 3D motion and structure analysis using motion parallax defined with respect to an arbitrary plane in the environment. It is shown that if an image coordinate system is warped using plane projective transformation with respect to a reference view, the residual image motion is dependent only on the epipoles and has a simple relation to the 3D structure. The author's computational scheme avoids point/line correspondence and is based on hierarchical estimation and image warping working directly with spatio-temporal image intensities. Results on real images demonstrate how this analysis simplifies ego and multiple motion analysis, and stable scene-centered 3D reconstruction.
67 citations
TL;DR: A new approach to correct for head motion in brain SPECT is developed, and for all simulated movements, the motion corrected images exhibited better agreement with a motion free reconstruction than did the uncorrected images.
Abstract: Patient motion occurring during data acquisition in single photon emission computed tomography (SPECT) can cause serious reconstruction artefacts. The authors have developed a new approach to correct for head motion in brain SPECT. Prior to motion, projections are assigned to conventional projections. When head motion occurs, it is measured by a motion monitoring system, and subsequent projection data are mapped to 'virtual' projections. The appropriate position of each virtual projection is determined by applying the converse of the patient's accumulated motion to the actual camera projection. Conventional and virtual projections, taken together, form a consistent set that can be reconstructed using a three-dimensional (3D) algorithm. The technique has been tested on a range of simulated rotational movements, both within and out of the transaxial plane. For all simulated movements, the motion corrected images exhibited better agreement with a motion free reconstruction than did the uncorrected images. This technique may help to overcome one of the major remaining limitations on image quality and quantitative accuracy in SPECT.
65 citations
TL;DR: It is shown that the single-slice rebinning algorithm is a good compromise between sensitivity, speed, and accuracy when compared to standard two-dimensional reconstruction, and a 3D reconstruction with alpha = 9 degrees.
Abstract: For volume-imaging PET scanners, no septa are used to maximize the sensitivity by collecting events oblique to the scanner axis. We answer two questions: (i) how does the performance of an image reconstruction algorithm for a volume-imaging PET scanner depend on its general dimensions? and (ii) at what point is a three-dimensional (3D) reconstruction algorithm needed for a volume-imaging scanner, as the axial extent is increased? A 3D reconstruction algorithm will accurately incorporate the oblique events in a reconstruction of the original source distribution. From simulations of an existing volume PET scanner with a maximum axial acceptance angle (+/-alpha) of alpha = 9 degrees, however, we show that the single-slice rebinning algorithm is a good compromise between sensitivity, speed, and accuracy when compared to standard two-dimensional reconstruction (alpha = 1 degrees), and a 3D reconstruction with alpha = 9 degrees. We also show with simulations that a new scanner with alpha = 27 degrees requires 3D reconstruction in order to achieve maximum sensitivity without unacceptable losses in accuracy. Measurements of scanner performance are based on a series of figures of merit that characterize image quality and quantitative accuracy measured from a set of simulated test phantoms.
60 citations
TL;DR: 3D reconstruction of selected color spectra of Doppler color flows and surrounding anatomy is feasible in the clinical setting and demonstrates the application of the algorithm to regurgitant and shunt jets with complex spatial and velocity patterns.
Abstract: A computer algorithm has been developed for segmentation and three-dimensional (3D) reconstruction of Doppler color-flow images. The algorithm enables the user to select a range of velocities, represented by colors, for segmentation and subsequent 3D reconstruction. The reconstructed flows are assigned a color palette and merged with the volume-rendered gray-scale image to produce a 3D image containing both flow and anatomic information. The results demonstrate the application of the algorithm to regurgitant and shunt jets with complex spatial and velocity patterns. We conclude that 3D reconstruction of selected color spectra (e.g., velocities) of Doppler color flows and surrounding anatomy is feasible in the clinical setting.
51 citations
Journal Article•
TL;DR: The different stages involved in the 3D reconstruction of arteries are defined and the solutions already proposed are reviewed to identify the true critical issues that are not often clearly mentioned in the literature and the challenges that they convey.
Abstract: The objective of this article is to define the different stages involved in the 3D reconstruction of arteries and to review, from our experience and from the literature, the solutions already proposed. A full reconstruction framework includes the characterization of the imaging device (in terms of distortion and calibration), the specificity of the image acquisition process, the preprocessing that can be applied, the detection of the vascular structures, the 2D feature formation, the reconstruction itself, and the visualization aspects. They are examined according to a computer vision approach where two or three views are assumed to be available. Their generalization to temporal image sequences are also considered. Some of the material reported here is unpublished. The article allows the reader to identify the true critical issues that are not often clearly mentioned in the literature and the challenges that they convey. A final discussion presents a few perspectives in this area of research.
49 citations
TL;DR: Using a biplane multidirectional isocentric X-ray system, a computer-aided simulation procedure was developed to calculate the 3D structure of the coronary arteries, and previously taken diagnostic angiograms were used to reconstruct the arterial structure and to select favorable views for the forthcoming intervention.
37 citations
08 May 1994
TL;DR: A novel method for radiographic stereo is described which takes into account the special imaging geometry of the digital X-ray sensor modeled by a linear moving array, or pushbroom, camera.
Abstract: There is considerable current interest in deriving accurate dimensional measurements of the internal geometry of complex manufactured parts, particularly castings. This paper describes an approach to the reconstruction of 3D part geometry from multiple digital X-ray images. A novel method for radiographic stereo is described which takes into account the special imaging geometry of the digital X-ray sensor modeled by a linear moving array, or pushbroom, camera. The 3D reconstruction algorithm employs a nominal geometric model which is perturbed by X-ray image constraints. Manufacturing applications are discussed and illustrated by experimental results on synthetic phantoms and actual casting images. >
34 citations
TL;DR: Recently, the authors have begun using a technique of computerized 3D reconstruction and recording which provides a true 3D display of the reconstructed images, similar to hearing full stereo audiophonic recording compared to monophonic, or to seeing in color rather than black and white.
Abstract: Fractures of the acetabulum can cause the pelvis to shatter into a wide array of complex configurations which can be difficult to fully delineate preoperatively. In addition to plain radiography and standard computed tomography, technology now allows the reconstruction of magnetic resonance imaging (MRI) and computed tomography (CT) data into virtual objects; three dimensional (3D) representations of anatomy which exist only within the computer memory. Printouts and photographs of 3D reconstructions provide another level of anatomic information to the orthopaedic surgeon. However, current standard displays such as computer and video screens and photographic and radiographic film are all two dimensional (2D) modalities. Displaying 3D reconstructions in this standard 2D fashion, inescapably robs the images of up to one third of the information contained within them--all the true depth information which is the essence of 3D. Shading techniques and perspective have both been utilized to simulate depth, but true depth is still lacking. Recently, the authors have begun using a technique of computerized 3D reconstruction and recording which provides a true 3D display of the reconstructed images. The resultant gain in image realism is profound, somewhat similar to hearing full stereo audiophonic recording compared to monophonic, or to seeing in color rather than black and white. The image generation and display process is a computerized mathematical adaptation of the photographic technique of stereophotography. Once in place, the technique is relatively simple to use and can be achieved in several ways with a minimum of additional hardware. Potential benefits lie in the method's ability to convey, in one 3D display, the true 3D, spatial anatomic configuration of the imaged pelvis. The methods described are common to those forming the fundamental basis for virtual reality imaging. Current users of some 3D reconstruction systems can now easily generate images which can be viewed with all of the depth information restored, into a true 3D display.
TL;DR: In this article, a single-slice rebinning with axial deconvolution (SSAD) method was proposed for a multi-ring PET scanner with retractable septa.
Abstract: A three-dimensional (3D) image reconstruction method, which was originally developed for a positron emission tomography (PET) system consisting of two rotating scintillation cameras, has now been implemented for a multi-ring PET scanner with retractable septa. The method is called 'single-slice rebinning with axial deconvolution' (SSAD), and can be described as follows. The projection data are sorted into transaxial 2D sinograms. Correction for the axial blurring is made by deconvolution in the sinograms. To obtain the axial spread functions, which depend on the activity distribution, 2D reconstruction is first made using a limited axial acceptance angle. The final 3D image is obtained by 2D reconstruction of transaxial planes. The method is simple but not approximate, has a modest memory requirement, and can be combined with different 2D techniques. Evaluations by Monte Carlo simulations and phantom studies have been made.
30 Oct 1994
TL;DR: The authors have implemented the EM reconstruction algorithm for volume acquisition from current generation retracted-septa PET scanners with extensive use of EM system matrix (C/sub ij/) symmetries, which reduces the storage cost and improves computational performance.
Abstract: The authors have implemented the EM reconstruction algorithm for volume acquisition from current generation retracted-septa PET scanners. Although the software was designed for a GE Advance scanner, it is easily adaptable to other 3D scanners. The reconstruction software was written for an Intel iPSC/860 parallel computer with 128 compute nodes. Running on 32 processors, the algorithm requires approximately 55 minutes per iteration to reconstruct a 128/spl times/128/spl times/35 image. No projection data compression schemes or other approximations were used in the implementation. Extensive use of EM system matrix (C/sub ij/) symmetries (including the 8-fold in-plane symmetries, 2-fold axial symmetries, and axial parallel line redundancies) reduces the storage cost by a factor of 188. The parallel algorithm operates on distributed projection data which are decomposed by base-symmetry angles. Symmetry operators copy and index the C/sub ij/ chord to the form required for the particular symmetry. The use of asynchronous reads, lookup tables, and optimized image indexing improves computational performance. Studies of the convergence of the 3D algorithm in comparison with that of the 2D algorithm are underway. >
09 Oct 1994
TL;DR: A direct method for the recovery of surface shape from image shading is presented, able to operate without explicit prerequisite information concerning the shape of the sought-after surface.
Abstract: A direct method for the recovery of surface shape from image shading is presented. The method in its basic form is applicable to shading patterns obtained when a distant overhead point light-source illuminates a convex or concave Lambertian surface possessing a single extremal point at which surface height has either a local maximum or local minimum. A key quality of the method is its ability to operate without explicit prerequisite information concerning the shape of the sought-after surface. Consideration is also given to the manipulation of images of more complex surface shapes.
TL;DR: It is shown that the proposed algorithm is less restrictive than existing methods for building a 3D model from arbitrary views.
16 Sep 1994
TL;DR: This work has shown that a recent optical flow algorithm has been shown to run in real-time on a standard scientific workstation and yields very accurate time-to-contact calculations.
Abstract: Currently two major limitations to applying computer vision to real-time robotic vision tasks are robustness in unsimulated and uncontrolled environments, and the computational resources required for real-time operation. In particular, many current visual motion detection algorithms (optical flow) are not suited for practical applications such as crash detection because they either require highly specialized hardware or up to several minutes on a scientific workstation. A recent optical flow algorithm [C94] however has been shown to run in real-time on a standard scientific workstation and yields very accurate time-to-contact calculations.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
14 Nov 1994
TL;DR: Three dimensional image reconstruction from cryo-electron micrographs allows the capsid structures of icosahedral viruses to be studied and parallel processing methods are devised and implemented to determine the orientations of virus particles.
Abstract: Three dimensional image reconstruction from cryoelectron micrographs allows the capsid structures of icosahedral viruses to be studied. The most computationally demanding stages of the reconstruction process are those that find and refine the orientations of the virus particles. We have devised and implemented parallel solutions to the problem of determining these orientations. By enabling determination of the orientations of far more particles than previously had been possible, parallel processing methods have contributed to improvements in the quality of recent reconstructions. >
01 Mar 1994
TL;DR: A real-time active stereo vision system incorporating gaze control and task directed vision is described, with emphasis on object tracking and object size and shape determination.
Abstract: A real-time active stereo vision system incorporating gaze control and task directed vision is described. Emphasis is placed on object tracking and object size and shape determination. Techniques include motion-centroid tracking, depth tracking, and contour tracking.
01 Mar 1994
TL;DR: In this article, the Locus method was extended for active range finder data to the stereo disparity mapping case, and a fast matching method was utilized that provided dense disparity maps, hence a disparity for each input pixel.
Abstract: The reconstruction of a surface having already matched corresponding points from stereo images (disparities) is a nontrivial task. This paper presents a new technique, the so-called Locus method, that exploits sensor geometry to efficiently build a terrain representation from stereo disparities. The power of this approach is the efficient and direct computation of a dense elevation map in arbitrary resolution. Additionally it proposes to solve problems like occlusions, ambiguities, and uncertainties caused by stereo matching errors. We extended the Locus method for active range finder data to the stereo disparity mapping case. For this reason, a newly developed fast matching method is utilized that provides dense disparity maps, hence a disparity for each input pixel. Once this data set is given, the Locus method can be applied in a straightforward and efficient way to gain a robust 3D reconstruction of the observed surface. It operates directly in image space, using dense and uniform measurements instead of first converting to object space. Experiments on synthetic and natural environment data show that the Locus method is less sensitive to disparity noise than traditional reconstruction.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
01 May 1994
TL;DR: The results indicate that the distortion correction techniques work well and were tested using experimental data acquired with the image intensifier-based volume tomographic angiography imaging system.
Abstract: An image intensifier-based rotational volume tomographic angiography imaging system has been constructed. The system consists of an x-ray tube and an image intensifier that are separately mounted on a gantry. This system uses an image intensifier coupled to a TV camera as a 2D detector so that a set of 2D projections can be acquired for a direct 3D reconstruction. Although an image intensifier offers good detection quantum efficiency and possibly results in a better low contrast resolution than a fluorescent screen, it introduces two types of distortion: S distortion and pincushion distortion. To obtain accurate reconstructions, these distortions must be corrected prior to 3D reconstruction. Techniques for the correction of these distortions have been developed. These techniques were tested using experimental data acquired with the image intensifier-based volume tomographic angiography imaging system. The results indicate that the distortion correction techniques work well.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: A bibliography of nearly 1300 references related to computer vision and image analysis, arranged by subject matter is presented, including computational techniques; feature detection and segmentation; image analysis; two-dimensional shape; pattern; color and texture; matching and stereo.
Abstract: This paper presents a bibliography of nearly 1300 references related to computer vision and image analysis, arranged by subject matter. The topics covered include computational techniques; feature detection and segmentation; image analysis; two-dimensional shape; pattern; color and texture; matching and stereo; three-dimensional recovery and analysis; three-dimensional shape; and motion. A few references are also given on related topics, such as geometry, graphics, coding and processing, sensors and optical processing, visual perception, neural nets, pattern recognition, and artificial intelligence, as well as on applications.
21 Jun 1994
TL;DR: A multiresolution system which integrates perceptual grouping, segmentation, stereo, shape from shading, and line labelling modules is proposed and implemented and the output of the integrated system is shown to be relatively insensitive to the constraints imposed by the individual modules.
Abstract: Individual cues from visual modules are fallible and often ambiguous. As a result, only integrated vision systems can be expected to give a reliable performance in practice. The design of such systems is challenging since each vision module works under different and possibly conflicting sets of assumptions. We have proposed and implemented a multiresolution system which integrates perceptual grouping, segmentation, stereo, shape from shading, and line labelling modules. The output of the integrated system is shown to be relatively insensitive to the constraints imposed by the individual modules. >
04 Apr 1994
TL;DR: The initial system for 3D reconstruction of neural tissue from transmission electron microscope (TEM) images has been improved and expanded in functionality and scope and is a completely digital, easy-to-use, quantifiable, and generalizable system.
Abstract: Our initial system for 3D reconstruction of neural tissue from transmission electron microscope (TEM) images has been improved and expanded in functionality and scope. An automated acquisition system captures images of tissue and controls the movement of a TEM. These images comprise a dataset of roughly one gigabyte. Using these data, software running on a Connection Machine automatically reassembles individual images into a single image of each section. An automated contour extraction and object classification algorithm is used and the objects to be reconstructed are selected by the user. Registration is completely automated, but the result is user verifiable and modifiable. The registration parameters are then used to realign both the contour and raw image data. The contour data are smoothed to average out noise, a surface grid is generated, and the resulting reconstruction is visualized. The image data can also be volume visualized. The result is a completely digital, easy-to-use, quantifiable, and generalizable system for 3D reconstruction from transmission electron microscope serial sections.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
05 Dec 1994
TL;DR: In the manufacturing domain it is easier to share data and provide machine perception based services because similar representations are commonly used in both shape design and engineering tools.
Abstract: Spline representations are widely used in CAGD as well as in computer graphics. Splines are also useful in many computer vision tasks. In particular, in the manufacturing domain it is easier to share data and provide machine perception based services because similar representations are commonly used in both shape design and engineering tools.
25 Feb 1994
TL;DR: It is shown that road-following commands can be generated from visual cues consisting of the projection into the image of the tangent point on the edge of the road, along with the optical flow of this point, and that lane markings can be robustly tracked in real time while confining all processing to the 2D image plane.
Abstract: The traditional approach to visual road following involves reconstructing a 3D model of the road. The model is in a world or vehicle-centered coordinate system, and it is symbolic, iconic, or a combination of both. Road-following commands (as well as other commands, e.g., obstacle avoidance) are then generated from this 3D model. Here we discuss an alternative approach in which a minimal road model is generated. The model contains only task-relevant information and a minimum of vision processing is performed to extract this information in the form of visual cues represented in the 2D image coordinate system. This approach leads to rapid and continuous update of the road model from the visual data. It results in inexpensive, fast, and robust computations. Road following is achieved by servoing on the visual cues in the 2D model. This approach results in a tight coupling of perception and action. In this paper, two specific examples of road following that use this approach are presented. In the first example, we show that road-following commands can be generated from visual cues consisting of the projection into the image of the tangent point on the edge of the road, along with the optical flow of this point. Using this cue, the resulting servo loop is very simple and fast. In the second example, we show that lane markings can be robustly tracked in real time while confining all processing to the 2D image plane. Neither knowledge of vehicle motion nor a calibrated camera is required. This system has been used to drive a vehicle up to 80 km/hr under various road conditions. The algorithm runs at a 15 Hz update rate.
01 Mar 1994
TL;DR: A CCD TV-camera-based system for real-time multicamera 2D detection of retro-reflective targets and software for accurate and fast 3D reconstruction, which can be found in the fields of sports, biomechanics, rehabilitation research, and various other areas of science and industry.
Abstract: The paper describes a CCD TV-camera-based system for real-time multicamera 2D detection of retro-reflective targets and software for accurate and fast 3D reconstruction. Applications of this system can be found in the fields of sports, biomechanics, rehabilitation research, and various other areas of science and industry. The new feature of real-time 3D opens an even broader perspective of application areas; animations in virtual reality are an interesting example. After presenting an overview of the hardware and the camera calibration method, the paper focuses on the real-time algorithms used for matching of the images and subsequent 3D reconstruction of marker positions. When using a calibrated setup of two cameras, it is now possible to track at least ten markers at 100 Hz. Limitations in the performance are determined by the visibility of the markers, which could be improved by adding a third camera.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
13 Nov 1994
TL;DR: A novel technique is proposed by which a computer may make an unsupervised identification of a given structure through a series of images, even if that structure includes so-called false contours or missing contours, for 3-D reconstruction of difficult-to-segment regions of the brain and abdomen.
Abstract: In order to obtain a 3-D reconstruction of the hippocampus from a volumetric MRI head study, it is necessary to separate it not only from the surrounding white matter, but also from contiguous areas of gray matter. At present it is necessary for a physician to manually segment the hippocampus on each slice of the volume in order to obtain such a reconstruction. The authors propose a novel technique by which a computer may make an unsupervised identification of a given structure through a series of images, even if that structure includes so-called false contours or missing contours. Applications include 3-D reconstruction of difficult-to-segment regions of the brain and abdomen, and volumetric measurements of organs from series of 2-D images. >
30 Oct 1994
TL;DR: The authors correct the degradation of X-ray angiograms due to scatter and veiling glare to improve contrast sensitivity of a 3D reconstructed image.
Abstract: The authors present a prototype system for three-dimensional (3D) image analysis of blood vessels using cone-beam CT. The purpose is to enhance the performance of clinician in assessing anatomical information such as the orientation of blood vessels, cross-sectional area, and volume of disease. The developed prototype system consists of two parts: 3D image reconstruction of blood vessels and analysis of the 3D blood vessel image. The Digital angiograms are collected in a short period of time by an X-ray rotational angiographic system using a CT gantry equipped with a cone-beam X-ray source and an image intensifier. The 3D reconstruction is performed by a short scan cone-beam filtered backprojection algorithm. The analysis of the 3D blood vessels image is based on a graph description obtained by a 3D binary thinning algorithm and a distance transformation of a 3D line pattern. A preprocessing of 3D reconstruction includes the correction of the geometrical distortions and the shading artifact introduced by the image intensifier. Furthermore, the authors correct the degradation of X-ray angiograms due to scatter and veiling glare to improve contrast sensitivity of a 3D reconstructed image. From results of the application to patient's abdominal blood vessels, the authors present the effectiveness of the system. >
13 Nov 1994
TL;DR: In this article, the most computationally demanding stages of the reconstruction process are those that find and refine the orientations of the virus particles, and they have devised and implemented parallel solutions to the problem of determining these orientations.
Abstract: Three dimensional image reconstruction from cryoelectron micrographs allows the capsid structures of icosahedral viruses to be studied. The most computationally demanding stages of the reconstruction process are those that find and refine the orientations of the virus particles. We have devised and implemented parallel solutions to the problem of determining these orientations. By enabling determination of the orientations of far more particles than previously had been possible, parallel processing methods have contributed to improvements in the quality of recent reconstructions.
21 Sep 1994
TL;DR: In this article, the reconstruction of quadric surfaces (cones and cylinders) from disparity measurements obtained by a stereo vision system is presented. But the prior approaches for quadrics in stereo vision have been more or less approximative.
Abstract: Techniques for the reconstruction of quadric surfaces (cones and cylinders) from disparity measurements obtained by a stereo vision system are presented. For the initial estimation of the geometrical parameters of cones, a regression based approach is adopted from [Newman, Flynn, and Jain, CVGIP: Image Understanding, Vol. 58, pp. 235-249]. A new method based on surface normal estimation is developed for the cylindrical case. For the refinement of the parameter estimates, the Levenberg-Marquardt nonlinear least squares algorithm is used as in [Flynn and Jain, Proc. 1988 IEEE Comput. Soc. Conf. Computer Vision and Pattern Recognition, pp. 261-267] but two mistaken formulas (one for a cone and the same for a cylinder) are corrected. The prior approaches for quadrics in stereo vision have been more or less approximative. Our contribution is to fit the exact quadric shape to disparity data using the existing methods for range data. The disparity space offers a convenient frame to analyze the differences between the measurements and the reconstructed model.