Reflectance and Shape from Images Using a Collinear Light Source

In this paper, a novel technique, called the photogeometric technique, is presented for surface reflectance extraction and surface recovery from an image sequence of a rotating object illuminated under a collinear light source (where the illuminant direction of the light source lies on or near the viewing direction of the camera). The rotation of the object is precisely controlled. The object surface is assumed to be smooth and uniform. The technique first computes the 3D locations of some surface points which give singular brightness values and builds the surface reflectance function by extracting the brightness values of these surface points from the image sequence. Then the technique uses the surface reflectance function and two images of the surface to recover surface depth and orientation simultaneously. The technique has been tested on real images of surfaces with different reflectance properties and geometric structures. The experimental results and comprehensive analysis show that the proposed technique is efficient and robust.     

Improving Shape from Shading with Interactive Tabu Search

Optimisation based shape from shading (SFS) is sensitive to initialization: errors in initialization are a significant cause of poor overall shape reconstruction. In this paper, we present a method to help overcome this problem by means of user interaction. There are two key elements in our method. Firstly, we extend SFS to consider a set of initializations, rather than to use a single one. Secondly, we efficiently explore this initialization space using a heuristic search method, tabu search, guided by user evaluation of the reconstruction quality. Reconstruction results on both synthetic and real images demonstrate the effectiveness of our method in providing more desirable shape reconstructions.     

Reflectance and Shape Estimation with a Light Field Camera Under Natural Illumination

International Journal of Computer Vision - Reflectance and shape are two important components in visually perceiving the real world. Inferring the reflectance and shape of an object through cameras...     

SFS方法及其与立体视觉方法的集成方案综述

立体视觉(StereoVision)方法是目前利用图象数据获取物体三维信息的主要方法之一。但该方法在图象灰度变化较缓慢的区域,由于难以准确地进行图象间的象素配对,而严重影响了它的效果。利用从明暗重构物体三维表面形状(ShapefromShading,简称SFS)的方法与该方法相结合,是改善重构结果的主要途径之一。文章通过分析SFS问题本身的不适定性,揭示了目前几类主要的SFS算法在可靠性、稳定性、局限性以及实用性方面所存在的问题,并在此基础上,简要地介绍了四类SFS与立体视觉方法相结合的形式,说明了通过利用立体视觉为SFS补充辅助的信息来消除SFS问题的不适定性,并对过去SFS的实现方法进行有效的改进,它是提高集成系统准确性的关键。     

恢复表面形状的冗余光源光度法的直接解法

介绍了一种由多幅图像恢复表面方向的直接方法。该方法中由于引入了冗余光源使噪声的影响降低了。用Moore Penrose逆法求解可得到优化解。无需建立对误差敏感的查找表。     

正则化方法在线性SFS问题中的应用

线性ShapefromShading问题(LSFS)是一类特殊的ShapefromShading问题,此时反射图是表面梯度分量的线性组合的函数。文章在待恢复表面平滑和已知光照方向等假定下,把线性SFS问题正则化,并利用Kaczmarz算法求解得到线性方程组。此种方法能处理区域形状不规则和边界条件不完备的情况。文章用Kaczmarz算法给出了一种从不可积向量场求得最接近的可积向量场的方法,该方法能处理区域形状不规则的情况。     

一种基于多面体模型的从明暗恢复物体形状方法

针对目前“从明暗恢复物体形状方法”存在的问题,提出了以多面体模型为基础的快速算法,根据向量场的分布建立关于物体表面深度信息的超定线性方程组,在最小二乘意义下求得物体表面的深度值。该算法能从已知光照条件下的单幅或多幅图像中恢复物体表面的三维结构,形成以像素为精度的物体表面多面体模型。实际计算表明该算法计算速度快,能适应单一反射系数的任意物体表面的形状恢复。     

基于混合反射模型的SFS有限元方法的研究

提出了基于混合反射模型的由明暗恢复物体三维形状的有限元算法。用正方形面元逼近光滑曲面,把曲面表示为所有节点基函数的线性组合;基于既含有漫反射成分又有镜面反射成分的混合模型,结合节点基函数,将反射图线性化。考虑数字图像的特点,直接使用离散形式的SFS问题的亮度约束形式,用最小化方法得到高度满足的线性方程;使用Kaczmarz算法计算出表面三维形状。使用合成图像和实际图像验证该文算法的有效性,探讨了该算法的性能。     

Shape optimization of an airfoil in a BZT flow with multiple-source uncertainties

Bethe–Zel’dovich–Thompson fluids (BZT) are characterized by negative values of the fundamental derivative of gasdynamics for a range of temperatures and pressures in the vapor phase, which leads to non-classical gasdynamic behaviors such as the disintegration of compression shocks. These non-classical phenomena can be exploited, when using these fluids in Organic Rankine Cycles (ORCs), to increase isentropic efficiency. A predictive numerical simulation of these flows must account for two main sources of physical uncertainties: the BZT fluid properties often difficult to measure accurately and the usually fluctuating turbine inlet conditions. For taking full advantage of the BZT properties, the turbine geometry must also be specifically designed, keeping in mind the geometry achieved in practice after machining always slightly differs from the theoretical shape. This paper investigates some efficient procedures to perform shape optimization in a 2D BZT flow with multiple-source uncertainties (thermodynamic model, operating conditions and geometry). To demonstrate the feasibility of the proposed efficient strategies for shape optimization in the presence of multiple-source uncertainties, a zero incidence symmetric airfoil wave-drag minimization problem is retained as a case-study. This simplified configuration encompasses most of the features associated with a turbine design problem, as far the uncertainty quantification is concerned. A preliminary analysis of the contributions to the variance of the wave-drag allows to select the most significant sources of uncertainties using a reduced number of flow computations. The resulting mean value and variance of the objective are next turned into metamodels. The optimal Pareto sets corresponding to the minimization of various substitute functions are obtained using a genetic algorithm as optimizer and their differences are discussed.     

Development of an Earthworm Robot with a Shape Memory Alloy and Braided Tube

Peristalsis motion like an earthworm has attracted attention in recent years because the movement is useful to progress in small spaces. An earthworm robot with a shape memory alloy, the BioMetal Helix, and a polyester braided tube was studied. The BioMetal is a fiber-like actuator-like muscle tissue; the BioMetal Helix (BMX series) was chosen to obtain good unit contraction force. The BMX, elongated at room temperature, becomes stiff and sharply contracts when a current is fed through it. For the unit expansion force, a polyester braided tube was used. The braided tube maintains a long and thin shape without compression, and when an external force presses the tube in the axial direction, it becomes shorter and thicker. When the external force is removed, the tube lengthens and becomes longer and thinner again. A prototype robot consisting of four units was developed. The robot was designed with three-dimensional computer-aided design, and the expansion and contraction timing of units was calculated through computer simulations. The simulated results closely resembled the experiments and the robot was improved by adaptation according to the simulated results.     

Determining Generative Models of Objects Under Varying Illumination: Shape and Albedo from Multiple Images Using SVD and Integrability

We describe a method of learning generative models of objects from a set of images of the object under different, and unknown, illumination. Such a model allows us to approximate the objects' appearance under a range of lighting conditions. This work is closely related to photometric stereo with unknown light sources and, in particular, to the use of Singular Value Decomposition (SVD) to estimate shape and albedo from multiple images up to a linear transformation (Hayakawa, 1994). Firstly we analyze and extend the SVD approach to this problem. We demonstrate that it applies to objects for which the dominant imaging effects are Lambertian reflectance with a distant light source and a background ambient term. To determine that this is a reasonable approximation we calculate the eigenvectors of the SVD on a set of real objects, under varying lighting conditions, and demonstrate that the first few eigenvectors account for most of the data in agreement with our predictions. We then analyze the linear ambiguities in the SVD approach and demonstrate that previous methods proposed to resolve them (Hayakawa, 1994) are only valid under certain conditions. We discuss alternative possibilities and, in particular, demonstrate that knowledge of the object class is sufficient to resolve this problem. Secondly, we describe the use of surface consistency for putting constraints on the possible solutions. We prove that this constraint reduces the ambiguities to a subspace called the generalized bas relief ambiguity (GBR) which is inherent in the Lambertian reflectance function (and which can be shown to exist even if attached and cast shadows are present (Belhumeur et al., 1997)). We demonstrate the use of surface consistency to solve for the shape and albedo up to a GBR and describe, and implement, a variety of additional assumptions to resolve the GBR. Thirdly, we demonstrate an iterative algorithm that can detect and remove some attached shadows from the objects thereby increasing the accuracy of the reconstructed shape and albedo.     

Shape design optimization of an expansion step in a channel with moving boundaries for a viscous flow

A shape design optimization problem for viscous flows has been investigated in the present study. An analytical shape design sensitivity expression has been derived for a general integral functional by using the adjoint variable method and the material derivative concept of optimization. A channel flow problem with a backward facing step and adversely moving boundary wall is taken as an example. The shape profile of the expansion step, represented by a fourth-degree polynomial, is optimized in order to minimize the total viscous dissipation in the flow field. Numerical discretizations of the primary (flow) and adjoint problems are achieved by using the Galerkin FEM method. A balancing upwinding technique is also used in the equations. Numerical results are provided in various graphical forms at relatively low Reynolds numbers. It is concluded that the proposed general method of solution for shape design optimization problems is applicable to physical systems described by nonlinear equations.     

Segmentation of a Vector Field: Dominant Parameter and Shape Optimization

Vector field segmentation methods usually belong to either of three classes: methods which segment regions homogeneous in direction and/or norm, methods which detect discontinuities in the vector field, and region growing or classification methods. The first two classes of method do not allow segmentation of complex vector fields and control of the type of fields to be segmented, respectively. The third class does not directly allow a smooth representation of the segmentation boundaries. In the particular case where the vector field actually represents an optical flow, a fourth class of methods acts as a detector of main motion. The proposed method combines a vector field model and a theoretically founded minimization approach. Compared to existing methods following the same philosophy, it relies on an intuitive, geometric way to define the model while preserving a general point of view adapted to the segmentation of potentially complex vector fields with the condition that they can be described by a finite number of parameters. The energy to be minimized is deduced from the choice of a specific class of field lines, e.g. straight lines or circles, described by the general form of their parametric equations. In that sense, the proposed method is a principled approach for segmenting parametric vector fields. The minimization problem was rewritten into a shape optimization and implemented by spline-based active contours. The algorithm was applied to the segmentation of precomputed optical flow fields given by an external, independent algorithm. Tristan Roy graduated from Ecole Centrale de Lille, France, in 2001. He is currently a Ph.D. student in mathematics at UCLA. His current research interests are variational analysis, optimization problems and PDEs. Fields of application are image segmentation and restoration. Eric Debreuve received his Ph.D. in Image Processing from the University of Nice-Sophia Antipolis, France, in 2000. He was a postdoctoral fellow at the Medical Imaging Research Laboratory (now UCAIR), University of Utah, Salt Lake City, for two years. He is currently a research scientist of the CNRS (a national research institute of France) at Laboratory I3S, University of Nice-Sophia Antipolis, France. His current research interests are image and video segmentation using active contours. Michel Barlaud received his These d'Etat from the University of Paris XII and Agregation de Physique (ENS Cachan). He is currently a Professor of Image Processing at the University of Nice-Sophia Antipolis, and the leader of the Image Processing group of I3S. His research topics are: Image and Video coding using Scan Based Wavelet Transform, Inverse problem using Half Quadratic Regularization and, Image and Video Segmentation using Region Based Active Contours and PDE's. He is a regular reviewer for several journals, a member of the technical committees of several scientific conferences. He leads several national research and development projects with French industries, and participates in several international academic collaborations: European Network of Excellence SCHEMA and SIMILAR (Louvain La Neuve (Belgium), ITI Greece, Imperial College …) and NSF-CNRS Funding (Universities of Stanford and Boston). He is the author of a large number of publications in the area of image and video processing, and the Editor of the book “Wavelets and Image Communication” Elsevier, 1994. Gilles Aubert received the These d'Etat es-sciences Mathematiques from the University of Paris 6, France, in 1986. He is currently professor of mathematics at the University of Nice-Sophia Antipolis and member of the J.A.Dieudonne Laboratory at Nice, France. His research interests are calculus of variations, nonlinear partial differential equations and numerical analysis; fields of application including image processing and, in particular, restoration, segmentation, optical flow and reconstruction in medical imaging.     

Behavioral detection of malware: from a survey towards an established taxonomy

Behavioral detection differs from appearance detection in that it identifies the actions performed by the malware rather than syntactic markers. Identifying these malicious actions and interpreting their final purpose is a complex reasoning process. This paper draws up a survey of the different reasoning techniques deployed among the behavioral detectors. These detectors have been classified according to a new taxonomy introduced inside the paper. Strongly inspired from the domain of program testing, this taxonomy divides the behavioral detectors into two main families: simulation-based and formal detectors. Inside these families, ramifications are then derived according to the data collection mechanisms the data interpretation, the adopted model and its generation, and the decision support.     

Taguchi's Method Analysis of an FMS Under Review-Period-Based Operational Controls: Identification of Control Periodicity

Flexibility of flexible manufacturing systems (FMSs) has been considered as an effective tool to compete in the present manufacturing environment. Enormous research efforts have been made to harness the benefits of flexibility through superior control strategies. While modeling flexibility and control strategies, researchers have mostly assumed an information system that can provide real-time control. Literature qualitatively reports that the real-time control can be highly capital intensive and difficult to achieve. This paper focuses on FMS operating under review-period (RP)-based control and presents a combined study of routing flexibility (RF), control strategies, and information system under Taguchi's method using simulation. RP-based control for FMS has been compared with real-time control. This paper contributes an approach for the decision maker to study the performance of an FMS operating under RP control and to identify the periodicity (time interval) of RP that will not deteriorate its performance in comparison to real-time control. It also helps the decision maker to reach a tradeoff between RP-based control and real-time control. The results show that RP-based control can be effectively implemented on an FMS having lower RF level. RP-based control can outperform real-time control with a superior control strategy and smaller RP size. The results under Taguchi's method suggest that the RF and control strategy should have maximum relative percentage contributions in FMS performance, whereas contribution of the RP (information system) should be minimum. Increasing the relative percentage contribution of the information system may deteriorate the performance of FMS. The information system is needed as a catalyst to facilitate the contributions of other factors in improving the FMS performance and not its own contribution     

Software testing with code-based test generators: data and lessons learned from a case study with an industrial software component

Automatically generating effective test suites promises a significant impact on testing practice by promoting extensively tested software within reasonable effort and cost bounds. Code-based test generators rely on the source code of the software under test to identify test objectives and to steer the test case generation process accordingly. Currently, the most mature proposals on this topic come from the research on random testing, dynamic symbolic execution, and search-based testing. This paper studies the effectiveness of a set of state-of-the-research test generators on a family of industrial programs with nontrivial domain-specific peculiarities. These programs are part of a software component of a real-time and safety-critical control system and integrate in a control task specified in LabVIEW, a graphical language for designing embedded systems. The result of this study enhances the available body of knowledge on the strengths and weaknesses of test generators. The empirical data indicate that the test generators can truly expose subtle (previously unknown) bugs in the subject software and that there can be merit in using different types of test generation approaches in a complementary, even synergic fashion. Furthermore, our experiment pinpoints the support for floating point arithmetics and nonlinear computations as a major milestone in the path to exploiting the full potential of the prototypes based on symbolic execution in industry.     

Selecting a Single Result from an Aggregate of Contradictory Alternatives with Use of Multiset Theory

Journal of Computer and Systems Sciences International - We consider basic approaches to decision-making using computer systems. Ambiguous results in decision-making are obtained through the use of...     

Depth extraction using a single moving camera: an integration of depth from motion and depth from stereo

An integrated approach to extract depth, efficiently and accurately, from a sequence of images is presented in this paper. The method combines the ability of the stereo processing to acquire highly accurate depth measurements and the efficiency of spatial and temporal gradient analysis. As a result of this integration, depth measurements of high quality are obtained at a speed approximately ten times greater than that of stereo processing. Without any a priori information of the locations of the points in the scene, the correspondence problem in stereo processing is computationally expensive. In our approach, we use spatial and temporal gradient (STG) analysis, which has been shown to provide depth with great efficiency, but limited accuracy, to guide the matching process of stereo. The camera motion used in the approach can be either lateral or axial. Extensive experiments on real scenes have shown the ability of the integrated approach to acquire depth with a mean error of less than 3%.