摘要:

AbstractA large number of cameras may be modeled quite accurately using the simple pinhole camera model, which may be defined either in terms of camera parameters or by thecmatrix (which defines the mapping from 3D points to the image plane). We present formulations of the associated transformations between these two equivalent representations. We also introduce an inexpensive technique for calibrating a camera using a single two‐plane calibration object, and employ a novel high‐precision Hough transform technique for determinings calibration grid lines.©1994 John Wiley&Son

ISSN:0899-9457    

DOI:10.1002/ima.1850050102

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractTo improve the resolution and image quality of the SFDT (Sigle‐Frequency Diffraction Tomography), a special fast multi‐frequency imaging method: Multi‐Frequency Backscattering Tomography (MFBT) is introduced in this paper. The method uses only the backscattered waves (after plane wave decomposition) while maintaining the merit of multi‐frequency method. The method is formulated for both the constant and vertically varying backgrounds. For the latter case the WKBJ approximation is used for the background Green's function. Formulas are derived both for volume scattering using the Born approximation and for boundary scattering using the physical optics approximation. Two reconstruction methods are presented. The backpropagation method can be used and has the same computation speed for both the constant and vertically varying backgrounds. Meanwhile the direct FT method is only formulated for the constant background, in which the backpropagation in z‐direction is implemented by FFT and therefore the computation speed is significantly increased. Compared with the SFDT using backpropagation reconstruction, the MFBT is nearlyNz/log2Nzfaster, whereNzis the number of grid points in z‐direction, and at the same time has a much better resolution and image quality. WhenNzis big, the time saving is remarkable. Compared with other multi‐frequency methods such as the multi‐frequency holography (prestack migration), the speeding factor becomesNfNz/log2Nz, whereNf, is the number of frequencies used. Numerical simulations for both constant and vertically varying backgrounds are performed to demonstrate the feasibility of the method and the quality of reconstructed images for different situations. Examples are also given to show that when the reconstruction procedure of constant background is applied to the case of vertically varying background, the image quality will be greatly deteriorated.©1994 Jo

ISSN:0899-9457    

DOI:10.1002/ima.1850050103

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractInverse scattering algorithms forHzpolarized waves are scarce, due to the added difficulties of polarization charges. Nevertheless, the polarization charges cannot be ignored for 3D problems as well as for 2DHzproblems. This work aims to reconstruct arbitrary inhomogeneous dielectric objects fromHzscattering data using a new formulation that abandons the standard integral equation model for aT‐matrix model. This new algorithm, called local shape‐function (LSF) imaging, is modified for dielectric objects withHzincident fields, where previously the LSF algorithm was applied to metallic objects withEzincident fields. The advantage of the LSF algorithm is a more accurate modeling of the induced interfacial polarization charges. For comparison, theHzdistorted Born iterative method using integral equations is shown to be valid only for small contrasts, while the LSF algorithm converges for much larger dielectric contrasts.©1994 John Wiley&Son

ISSN:0899-9457    

DOI:10.1002/ima.1850050104

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractWe describe an application of the nonlinear deconvolution algorithm CLEAN in which aprioriknowledge of the point‐spread function allows transmission of nonredundant information. We refer to this as CLEAN compression. The point‐spread function is viewed as a redundancy function. The data set may be regarded as a convolution of the nonredundant information with the redundancy function. Since the nonredundant data is a small subset of the overall data set, images or telecommunication messages may be transmitted over narrowband channels using CLEAN. Effective analog data compression is maximized; the analog signal may be significantly compressed with CLEAN even before any additional compression or digital encoding algorithms are applied.©1994 John Wiley&Son

ISSN:0899-9457    

DOI:10.1002/ima.1850050105

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractAn ultrasound‐device image‐reconstruction algorithm has been described previously that uses orthonomal wavelets as the basis of a transform space. The transform algorithms make it possible to analyze the reflected ultrasound signal from a sample to produce a map of one of its internal properties, the acoustical impedance. Conventional wavelets do not exhibit translation invariance, the lack of which ofttimes generates nonzero expansion coefficients for wavelets of lower sequency than the transmitted signal. By a transformation of basis to a set of functions which exhibit a form of translation invariance the aforementioned problem is removed. However, the new functions are no longer orthogonal. An algorithm is described to perform this transformation extremely efficiently. Also described is an algorithm to unsmear the image due to the fact that the transmitted signal may not be a single wavelet but instead is a short sequence (linear combination) of wavelets. The coefficients of the array used to deconvolve the signal are determined by performing a forward wavelet transformation on the transmitted signal itself.©1994 John Wiley&Son

ISSN:0899-9457    

DOI:10.1002/ima.1850050106

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThis work concerns an extension of usual radar imaging in which the pictures of the target do not simply exhibit the position of elementary reflectors but also give the behavior of these reflectors when the frequency and the direction of illumination vary. Essentially, the technique consists of describing the target by a generalized image which can be computed from the knowledge of the backscattering function on a large domain in the angle‐frequency space. A discussion of the physical relevance of the approach is given and its conclusions are used to derive a practical formulation relying on a special wavelet transform. The implementation of the technique is developed by using the fast Mellin transform. Special features of the method are the use of data in polar format without resampling and the fact that the computation can be easily parallelized.©1994 John Wiley&Sons

ISSN:0899-9457    

DOI:10.1002/ima.1850050107

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractA great deal of dynamic computer vision literature deals with the determination of motion and structure of rigid objects by observing points on objects at two or more time instants. In some situations point correspondences may not be available but line correspondences may be, such as when edges on the objects are visible. In this article we investigate the multiplicity of solutions when various numbers of line correspondences among several snapshots of an object are known. The case given the most consideration is that in which the object is moving with constant motion, that is, with constant rotation about an unknown center which itself is moving with constant translation. In this case we show that there is a unique solution given three line correspondences over three frames, two line correspondences over four frames, and one line correspondence over five or more frames. With fewer line correspondences there are infinitely many solutions. In the more general case where the motion is allowed to vary between successive frames, we show that there can be no more than 600 solutions to motion and structure with six line correspondences over three views, and that there is a unique solution with seven line correspondences. Several examples are given to illustrate our results.©1994 John Wiley&Sons In

ISSN:0899-9457    

DOI:10.1002/ima.1850050108

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractTomographic velocity estimation of a three‐dimensional (3D) anomaly as a function of time is implemented by the simultaneous iterative reconstruction technique (SIRT) using synthetic observed travel times as data. Rays are retraced every 6–7 iterations to ansure consistency between rays and velocities. An expanding steam front modeled within a shallow reservoir is imaged at two points in time using three different survey geometries containing both cross‐well and well‐to‐surface paths. Synthetic data can be used to evaluate and optimize survey design and resolution prior to field data acquisition. Resolution is evaluated by computing point spread functions and can (theoretically) be made as high as desired (up to the limit imposed by wave phenomena and the noise in the data) by increasing the number of independent observations and correspondingly reducing the image voxel size. ©1994 John Wile

ISSN:0899-9457    

DOI:10.1002/ima.1850050109

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

ISSN:0899-9457    

DOI:10.1002/ima.1850050101

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY