摘要:

AbstractWe propose a unification framework for three‐dimensional shape reconstruction using physically based models. A variety of 3D shape reconstruction techniques have been developed in the past two decades, such as shape from stereopsis, from shading, from texture gradient, and from structured lighting. However, the lack of a general theory that unifies these shape reconstruction techniques into one framework hinders the effort of a synergistical image interpretation scheme using multiple sensors/information sources. Most shape‐from‐Xtechniques use an “observable” (e.g., the stereo disparity, intensity, or texture gradient) and a model, which is based on specific domain knowledge (e.g., the triangulation principle, reflectance function, or texture distortion equation) to predict the observable, in 3D shape reconstruction. We show that all these “observable–prediction‐model” types of techniques can be incorporated into our framework of energy constraint on a flexible, deformable image frame. In our algorithm, if the observable does not confirm to the predictions obtained using the corresponding model, a large “error” potential results. The error potential gradient forces the flexible image frame to deform in space. The deformation brings the flexible image frame to “wrap” onto the surface of the imaged 3D object. Surface reconstruction is thus achieved through a “package wrapping” or a “shape deformation” process by minimizing the discrepancy in the observable and the model prediction. The dynamics of such a wrapping process are governed by the least action principle which is physically correct. A physically based model is essential in this general shape reconstruction framework because of its capability to recover the desired 3D shape, to provide an animation sequence of the reconstruction, and to include the regularization principle into the

ISSN:0899-9457    

DOI:10.1002/ima.1850030402

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractWe present a simple technique to model the structures and behaviors of flexible, elastic objects. We use an imaginary elastic wire frame, which is made of membranous, thin‐plate–type material, to model the surface structures of flexible objects. We demonstrate that in computational vision, such a flexible wire frame can be used for visual surface reconstruction with the structured‐light sensing technique. In graphic animation, we allow animation sequences to be generatedautomaticallybetween prespecified key frames, the surface structures of which are described by our flexible mode. Furthermore, we allow collisions of objects' trajectories so that interactions of multiple flexible objects can be simulated. We believe that our technique is widely applicable in many computational vision and graphic animation proc

ISSN:0899-9457    

DOI:10.1002/ima.1850030403

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractA comparison between the use of Fourier and Hartley transforms for motion estimation of multiple moving objects in image sequences is presented. The spectrum of the two transforms show that the temporal frequencies at the peaks (of the spectrum) is related to the velocity of the moving objects. The analysis shows that the Hartley technique is faster and requires less memory space than the Fourier technique. However, it gives the velocity of the moving objects but not the direction. The Fourier spectrum, on the other hand, gives the velocity and direction. An efficient implementation is possible by using the Hartley transform to estimate the temporal frequencies of the peaks and hence the velocities. The fast Fourier transform is then used to compute the spectrum at those peaks. The direction is easily found from the Fourier spectrum by reversing the sign of the temporal frequency corresponding to the peak.

ISSN:0899-9457    

DOI:10.1002/ima.1850030404

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractTwo methods of solving the nonlinear two‐dimensional electromagnetic inverse scattering problem in the time domain are considered. These are the Born iterative method and the method originally proposed by Tarantola for the seismic reflection inverse problems. The former is based on Born‐type iterations on an integral equation, whereby at each iteration the problem is linearized, and its solution is found via a regularized optimization. The latter also uses an iterative method to solve the nonlinear system of equations. Although it linearizes the problem at each stage as well, no optimization is carried out at each iteration; rather the problem as a whole is posed as a (regularized) optimization. Each method is described briefly and its computational complexity is analyzed. Tarantola's method is shown to have a lower numerical complexity compared to the Born iterative method for each iteration, but in the examples considered, required more iterations to converge. Both methods perform well when inverting a smooth profile; however, the Born iterative method gave better results in resolving localized point scatter

ISSN:0899-9457    

DOI:10.1002/ima.1850030405

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractWe present the recent developments of the Scanning Tomographic Acoustic Microscope (STAM). The STAM was proposed as a method to achieve 3D imaging capability for the Scanning Laser Acoustic Microscope (SLAM). With the addition of a quadrature receiver, the complex scattered wave field can now be detected, and consequently the STAM is capable of subsurface holographic and tomographic imaging. The resolution improvement of the STAM can be attributed directly to the detection of the phase information and the image reconstruction technique. The STAM is sensitive to phase errors in the tomographic projections. In particular, the quadrature phase error and the initial phase error in the complex projections are critical to the tomographic reconstruction process. For multiple‐angle tomography, high‐precision projection registration and alignment become necessary. By obtaining solutions to these implementation problems, we have succeeded in obtaining images superior to the original SLAM images. In addition, quantitative ultrasonic imaging is possible with the STAM, and a method is presented to image the velocity parameter of simple specimens. With these capabilities, the STAM may become a useful tool for high‐resolution subsurface nondestructive evalu

ISSN:0899-9457    

DOI:10.1002/ima.1850030406

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe possibility of reconstructing two‐dimensional electron‐density profiles in the ionosphere with ionospheric tomography is significant. However, due to the nature of the imaging system, there are several resolution degradation parameters. In order to compensate for these degradation parameters,a prioriinformation must be used. This article introduces the orthogonal decomposition algorithm for image reconstruction, which uses thea prioriinformation to generate a set of orthogonal basis functions for the source domain. This algorithm consists of two simple steps: orthogonal decomposition and recombination. In the development of the algorithm, it is shown that the degradation parameters of the imaging system result in correlations among projections of orthogonal functions. Gram–Schmidt orthogonalization is used to compensate for these correlations, producing a matrix that measures the degradation of the system. Any set of basis functions can be used, and depending upon this choice, the nature of the algorithm varies greatly. Choosing the basis functions of the source domain to be the Fourier kernels produces an algorithm capable of isolating individual frequency components of individual projections. This particular choice of basis functions also results in an algorithm that strongly resembles the direct Fourier method, but without requiring the use of inverse Fourier trans

ISSN:0899-9457    

DOI:10.1002/ima.1850030407

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

ISSN:0899-9457    

DOI:10.1002/ima.1850030401

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY