A system for digital reconstruction of gypsum dental casts

A range scanner is developed that can scan a gypsum dental cast and reconstruct the cast digitally for display and storage purposes. The scanner is based on subtractive light and computes the range values using optical triangulation. A fiducial marker is introduced that, when attached to a dental cast at the time of image acquisition, makes it possible to integrate multiview range images of the cast without image registration. A method for calibrating the scanner is described and experimental results showing the accuracy of the scanner are presented     

Multiview deblurring for 3-D images from light-sheet-based fluorescence microscopy

We propose an algorithm for 3-D multiview deblurring using spatially variant point spread functions (PSFs). The algorithm is applied to multiview reconstruction of volumetric microscopy images. It includes registration and estimation of the PSFs using irregularly placed point markers (beads). We formulate multiview deblurring as an energy minimization problem subject to L1-regularization. Optimization is based on the regularized Lucy-Richardson algorithm, which we extend to deal with our more general model. The model parameters are chosen in a profound way by optimizing them on a realistic training set. We quantitatively and qualitatively compare with existing methods and show that our method provides better signal-to-noise ratio and increases the resolution of the reconstructed images.     

A multiview microwave imaging system for two-dimensional penetrableobjects

A microwave imaging system is based on a multiview numerical solution to the integral equation of 2D transverse magnetic (TM) scattering is proposed. This solution is achieved by the moment method, and a pseudoinversion transformation is used to face ill-conditioning problems. All experimental setup is described that uses a scanning subsystem for measuring the values of the scattered electric field inside an observation domain located outside the investigation one (i.e., the area containing the cross sections of cylindrical dielectric scatters). Rotations of the investigation domain with respect to the scanning subsystem and the transmitting antenna allow a multiview imaging process. The imaging system does not require plane-wave illumination and does not use any first-order approximations; hence, it may be used even in the case of strong scatterers. The offline and once-and-for-all computation of the pseudoinverse matrix allows an inexpensive reconstruction in terms of computer resources. Some tests of the system were carried out, and the results are reported     

Optimizing Case-based detection performance in a multiview CAD system for mammography

When reading mammograms, radiologists combine information from multiple views to detect abnormalities. Most computer-aided detection (CAD) systems, however, use primitive methods for inclusion of multiview context or analyze each view independently. In previous research it was found that in mammography lesion-based detection performance of CAD systems can be improved when correspondences between MLO and CC views are taken into account. However, detection at case level detection did not improve. In this paper, we propose a new learning method for multiview CAD systems, which is aimed at optimizing case-based detection performance. The method builds on a single-view lesion detection system and a correspondence classifier. The latter provides class probabilities for the various types of region pairs and correspondence features. The correspondence classifier output is used to bias the selection of training patterns for a multiview CAD system. In this way training can be forced to focus on optimization of case-based detection performance. The method is applied to the problem of detecting malignant masses and architectural distortions. Experiments involve 454 mammograms consisting of four views with a malignant region visible in at least one of the views. To evaluate performance, five-fold cross validation and FROC analysis was performed. Bootstrapping was used for statistical analysis. A significant increase of case-based detection performance was found when the proposed method was used. Mean sensitivity increased by 4.7% in the range of 0.01-0.5 false positives per image.     

An electromagnetic imaging approach using a multi-illuminationtechnique

An approach to microwave imaging using a multi-illumination technique is proposed. The numerical solution is reached by a multi-illumination-angle multiview approach based on the moment method. The aim is to extend the application range of the Born approximation by utilizing a-priori information about a scatterer. The basic idea of the approach is outlined, and preliminary results are reported     

Optimising inter-view prediction structure for multiview video coding with minimum spanning tree

A new systematic method to construct a near-optimal inter-view prediction structure for multiview video coding is proposed based on the directed minimum spanning tree of inter-view prediction cost graph. The method is applicable to arbitrary irregular and dynamic changing camera arrangements. Results show that the generated structure achieves better compression efficiency than the reference structure of the joint multiview video model.     

An efficient and accurate method for the relaxation of multiview registration error.

This paper presents a new method for the relaxation of multiview registration error. The multiview registration problem is represented using a graph. Each node and each edge in the graph represents a 3-D data set and a pairwise registration, respectively. Assuming that all the pairwise registration processes have converged to fine results, this paper shows that the multiview registration problem can be converted into a quadratic programming problem of Lie algebra parameters. The constraints are obtained from every cycle of the graph to eliminate the accumulation errors of global registration. A linear solution is proposed to distribute the accumulation error to proper positions in the graph, as specified by the quadratic model. Since the proposed method does not involve the original 3-D data, it has low time and space complexity. Additionally, the proposed method can be embedded into a trust-region algorithm and, thus, can correctly handle the nonlinear effects of large accumulation errors, while preserving the global convergence property to the first-order critical point. Experimental results confirm both the efficiency and the accuracy of the proposed method.     

Microwave imaging within the second-order Born approximation:stochastic optimization by a genetic algorithm

This paper addresses the problem of reconstructing the location, shape, and dielectric permittivity distribution of an inhomogeneous dielectric object from measurements of the field scattered by the object. The object is an inhomogeneous infinite cylinder of arbitrary cross section illuminated by a transverse magnetic incident electric field. The approach is based on the Lippmann-Schuringer integral equation for the electromagnetic inverse scattering problem, approximated by applying the second-order Born approximation, which allows an extension of the range of contrast values that can be accurately imaged. The numerical approach is developed in the spatial domain and makes use of a multi-illumination multiview processing. In particular, the inverse problem is recast in a global nonlinear optimization problem (including a penalty function), solved by a stochastic method based on a genetic algorithm. In this paper, the mathematical formulation of the approach is described and the results of several dielectric reconstructions are reported, including comparisons with analogous reconstructions performed within the linearized (first-order) Born approximation     

A new fast motion estimation algorithm based on the loop–epipolar constraint for multiview video coding

There lie geometric constraints between neighboring frames in multiview video sequences. The geometric constraints are valuable for reducing spatial and temporal redundancy in multiview video coding (MVC). In this paper, we propose a new fast motion estimation algorithm based on the loop–epipolar constraint which combines loop and epipolar constraints. A practical search technique is designed according to the characteristics of the loop–epipolar constraint. Experimental results show that the proposed algorithm is efficient for sequences under different multiview camera setups.     

RD-optimized interactive streaming of multiview video with multiple encodings

This paper presents a rate-distortion (RD) optimized interactive streaming method for multiview video pre-compressed by H.264 Joint Multiview Video Model (JMVM). In the proposed method, multiple encodings are first used to facilitate the flexible server–client interaction. Second, a RD-optimized scheduling strategy is provided to guarantee the optimal view-dependent delivery of multiview video. In the RD-optimized scheduling strategy, a distortion model is proposed to estimate the expected end-to-end distortion by accounting for both coding and packet-loss-induced distortions, as well as rendering-induced distortion. With the end-to-end distortion model, the server can select the optimal encoding combination for transmission. Experimental results demonstrate that the proposed method can achieve a significant end-to-end RD performance improvement over the selective streaming methods with simulcast coding or scalable multiview coding. In addition, it has better error-resilience performance to combat with packet-losses over the Internet protocol (IP) networks.     

Medical imaging with a microwave tomographic scanner

A microwave tomographic scanner for biomedical applications is presented. It consists of a 64-element circular array with a useful diameter of 20 cm. Electronically scanning the transmitting and receiving antennas allows multiview measurements with no mechanical movement. Imaging parameters-a spatial resolution of 7 mm and a contrast resolution of 1% for a measurement time of 3 s-are appropriate for medical use. Measurements on tissue-simulating phantoms and volunteers, together with numerical simulations, are presented to assess the system for absolute imaging of tissue distribution and for differential imaging of physiological, pathological, and induced changes in tissues     

A multiview sequence CODEC with view scalability

A multiview sequence CODEC with flexibility, MPEG-2 compatibility and view scalability is proposed. We define a GGOP (Group of GOP) structure as a basic coding unit to efficiently code multiview sequences. Our proposed CODEC provides flexible GGOP structures based on the number of views and baseline distances among cameras. The encoder generates two types of bitstreams; a main bitstream and an auxiliary one. The main bitstream is the same as a MPEG-2 mono-sequence bitstream for MPEG-2 compatibility. The auxiliary bitstream contains information concerning the remaining multiview sequences except for the reference sequences. Our proposed CODEC with view scalability provides several viewers with realities or one viewer motion parallax whereby changes in the viewer’s position results in changes in what is seen. The important point is that a number of view points are selectively determined at the receiver according to the type of display modes. The viewers can choose an arbitrary number of views by checking the information so that only the views selected are decoded and displayed.The proposed multiview sequence CODEC is tested with several multiview sequences to determine its flexibility, compatibility and view scalability. In addition, we subjectively confirm that the decoded bitstreams with view scalability can be properly displayed by several types of display modes, including 3D monitors.     

Hybrid FE approach to evaluating edge effects in cavity-backedarrays

A numerical hybrid technique is presented which makes use of the finite element method (FEM) for introducing edge effects in the analysis of planar cavity-backed antenna arrays. The technique, based on an application of the equivalence principle, is first applied to a simplified configuration to demonstrate its effectiveness     

Hole‐Filling Methods Using Depth and Color Information for Generating Multiview Images

This paper presents new hole‐filling methods for generating multiview images by using depth image based rendering (DIBR). Holes appear in a depth image captured from 3D sensors and in the multiview images rendered by DIBR. The holes are often found around the background regions of the images because the background is prone to occlusions by the foreground objects. Background‐oriented priority and gradient‐oriented priority are also introduced to find the order of hole‐filling after the DIBR process. In addition, to obtain a sample to fill the hole region, we propose the fusing of depth and color information to obtain a weighted sum of two patches for the depth (or rendered depth) images and a new distance measure to find the best‐matched patch for the rendered color images. The conventional method produces jagged edges and a blurry phenomenon in the final results, whereas the proposed method can minimize them, which is quite important for high fidelity in stereo imaging. The experimental results show that, by reducing these errors, the proposed methods can significantly improve the hole‐filling quality in the multiview images generated.     

Multiview Image Acquisition and Projection

A solution for describing both the multiview image set, obtained with a parallel camera layout, and the perceived image in a projection-type full parallax multiview imaging system with a parallel projector layout, is derived. This is done with the use of 4times4 homogenous matrices to quantitatively analyze the image quality in the system. The solution provides a means of finding properties and/or behavior of the perceived image changes depending on the viewer's position in the system. The solution can analytically describe the appearance of three-dimensional images in the space generated by the multiview image set displayed on a projection screen     

基于光场结构特性与多视点匹配的深度估计

针对现有光场图像深度估计技术无法均衡地对主要对象和背景进行深度估计的问题,提出了一种基于光场结构特性与多视点匹配的深度估计方法。该方法在光场结构特性引导的深度估计的基础上,为了实现光场图像深度变化区域的平滑过渡,同时又考虑光场图像具有多视点子孔径图像阵列的特点,采用多视点匹配优化光场图像深度估计。在马尔可夫随机域中,基于光场结构特性构建深度估计平滑项,同时联合多视点匹配构建深度估计数据项,并进行全局深度迭代优化,从而有效平衡对象深度边界和背景深度估计,提高光场图像深度估计的性能。实验结果表明,所提出的方法能够得到更加清晰的深度边界,同时可以修正背景中不准确的深度值,获得高质量的深度估计结果。     

On the use of regularization techniques in numericalinverse-scattering solutions for microwave imaging applications

This paper deals with integral-equation-based numerical methods for microwave imaging using regularization procedures to overcome ill-conditioning problems. The strong dependence of reconstruction quality on “a priori” information is discussed. Such information is required to select a suitable number of independent columns when using truncated pseudoinversions (or other regularization parameters, in different cases) for accurate dielectric reconstructions. Moreover, a criterion for the choice of the optimal number of independent columns is proposed, and the possibility of making this choice less critical by using a multiview version of the method is explored. Finally, a modified procedure is presented that further increases the range from which to choose the number of independent columns that allows one to achieve acceptable reconstructions     

基于SIFT 匹配的多视点立体图像零视差调整

针对目标跟踪过程中目标可能出现的快速变化和严重遮挡等问题,提出了一种基于新的子空间表示的目标跟踪算法。采用距离不变量对尺度不变特征变换(SIFT)特征点匹配对进行提纯。用提纯后的特征点匹配对,通过线性拟合得到仿射变化参数。在粒子滤波的理论框架下,采用快速的迭代算法,建立目标的主分量(PCA)子空间表示,结合计算得到的仿射变化参数,构造有效的目标观测模型完成跟踪。同时,采用在线学习的方法对SIFT特征点和PCA子空间进行定时更新。大量实验表明,提出的算法能快速有效地完成对姿态和形状剧烈变化的目标的精确跟踪。     

重建有耗单层媒质和背景媒质的回归圆方法

本文提出重建有耗单层媒质的回归圆方法。在高频部分,以波数k为因变量的反射系数轨迹形成一个圆,根据圆心和半径,不需使用任何数值方法即可重建出媒质特性。此方法既适用于已知复反射系数谱,又适用于只知道反射系数振幅情况,从而使本方法更实用。     

一种级联喇曼光纤激光器数值模拟的新算法

为了优化设计光纤喇曼激光器的各项参量,采用喇曼激光器的基本理论模型模拟,提出了非线性最小二乘法和龙格-库塔法相结合的新算法,解决了模型中存在的两点边值问题,得到了级联喇曼光纤激光器的输出特性以及最佳光纤长度、激光阈值和斜率效率。结果表明,新算法非常有效,数值模拟的结果和相关实验相吻合。