Low‐cost solution to on‐line color filter array demosaicking

The article introduces a low‐cost algorithm for improving the demosaicking process in the texture areas such as one‐pixel patterns. The algorithm first detects difficult texture regions. After the detection process is completed, the algorithm demosaicks the texture areas using special demosaicking operations whereas non‐texture regions are restored using some of the existing demosaicking approaches. In this way, the quality of the texture areas in demosaicked images can be improved up to 70% while only little increasing the computational complexity of the original demosaicking solution. © 2007 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 17, 232–243, 2007     

无方位模糊的非均匀稀疏阵MVDR测向方法

稀疏阵能够获得更大的阵列孔径,但常规波束形成(Conventional Beam-Forming,CBF)对非均匀稀疏阵测向时会出现方位模糊。提出了一种基于最小方差无畸变响应(Minimal Variance Distortionless Response,MVDR)同局部非稀疏的非均匀稀疏阵(Non-Uniform Sparse Array,NUSA)的设计相结合来抑制方位模糊的方法(NUSA+MVDR),对其无方位模糊现象进行了理论分析,表明MVDR这一非线性处理方法对伪峰有很好的抑制能力。针对一种典型的NUSA(Typical NUSA,TNUSA),进行了TNUSA+MVDR数值仿真实验,其结果和理论分析一致,表明:1 MVDR有很强的NUSA检测能力,在所给仿真条件下,等效阵元间距为50倍波长时,仍能很好地抑制方位模糊;2TNUSA+MVDR较阵元数相同的均匀非稀疏阵列的CBF和MVDR有更高的方位分辨力;3阵元数一定,TNUSA+MVDR方位分辨力随着等效间距增加而提高,最小可分辨角度反比于等效间距;4等效间距一定,TNUSA+MVDR方位分辨力随阵元数增加而增加。海上实验在等效阵元间距为10倍波长条件下部分验证了NUSA+MVDR的检测性能。     

被动定向浮标阵卡尔曼滤波目标跟踪研究

文章研究利用被动定向浮标阵定位跟踪水下机动目标的方法,基于卡尔曼滤波(Kalman Filter, KF)原理提出一种定位跟踪滤波器的具体实现方法。该方法能够整合多枚浮标现在及过去有误差的测量数据,提高定位精度,同时连续输出水下目标运动参数估计从而锁定目标运动轨迹。该方法实现的关键在于建立水下目标与浮标阵的数学迭代运算模型,包括状态空间的动态与观测过程。由于被动定向浮标阵目标跟踪是一个非线性估计问题,而卡尔曼滤波器是线性的,因此文章设计了近似的线性观测方程以利用卡尔曼滤波来解决这个问题。通过计算机仿真研究该滤波器的跟踪效果并与最小二乘法进行比较,估计精度明显高于最小二乘法。同时通过仿真验证该滤波器可以自适应跟踪目标的非稳态运动过程。该方法在工程实践上具有一定应用前景与指导意义。     

Enhanced mixed interpolation XFEM formulations for discontinuous Timoshenko beam and Mindlin‐Reissner plate

Shear locking is a major issue emerging in the computational formulation of beam and plate finite elements of minimal number of degrees of freedom as it leads to artificial overstiffening. In this paper, discontinuous Timoshenko beam and Mindlin‐Reissner plate elements are developed by adopting the Hellinger‐Reissner functional with the displacements and through‐thickness shear strains as degrees of freedom. Heterogeneous beams and plates with weak discontinuity are considered, and the mixed formulation has been combined with the extended finite element method (FEM); thus, mixed enrichment functions are used. Both the displacement and the shear strain fields are enriched as opposed to the traditional extended FEM where only the displacement functions are enriched. The enrichment type is restricted to extrinsic mesh‐based topological local enrichment. The results from the proposed formulation correlate well with analytical solution in the case of the beam and in the case of the Mindlin‐Reissner plate with those of a finite element package (ABAQUS) and classical FEM and show higher rates of convergence. In all cases, the proposed method captures strain discontinuity accurately. Thus, the proposed method provides an accurate and a computationally more efficient way for the formulation of beam and plate finite elements of minimal number of degrees of freedom.     

Lossless color medical image compression using adaptive block‐based encoding for human computed tomographic images

The advancement in medical imaging systems such as computed tomography (CT), magnetic resonance imaging (MRI), positron emitted tomography (PET), and computed radiography (CR) produces huge amount of volumetric images about various anatomical structure of human body. There exists a need for lossless compression of these images for storage and communication purposes. The major issue in medical image is the sequence of operations to be performed for compression and decompression should not degrade the original quality of the image, it should be compressed loss lessly. In this article, we proposed a lossless method of volumetric medical image compression and decompression using adaptive block‐based encoding technique. The algorithm is tested for different sets of CT color images using Matlab. The Digital Imaging and Communications in Medicine (DICOM) images are compressed using the proposed algorithm and stored as DICOM formatted images. The inverse process of adaptive block‐based algorithm is used to reconstruct the original image information loss lessly from the compressed DICOM files. We present the simulation results for large set of human color CT images to produce a comparative analysis of the proposed methodology with block‐based compression, and JPEG2000 lossless image compression technique. This article finally proves the proposed methodology gives better compression ratio than block‐based coding and computationally better than JPEG 2000 coding. © 2013 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 23, 227–234, 2013     

A technique of object‐adaptive vertex‐based shape coding for MPEG‐4 videos

The MPEG‐4 visual standard is the first international standard that allows the transmission of arbitrarily shaped video objects and provides technologies to view, access, and manipulate objects rather than pixels. It addresses the encoding of video objects by shape coding, motion estimation, and texture coding for interactivity, high compression, and scalability. Current binary shape‐coding techniques can be classified into two categories: bitmap based and contour based. O'Connell (1997) proposed an object‐adaptive vertex‐based shape‐coding method to improve the efficiency of shape coding. This method encodes the relative locations of a video object's vertices by adapting the representation to the dynamic range of the relative locations and by exploiting an octant‐based representation for each relative location. We propose an extension of O'Connell's method. Two relative locations of a video object's vertices are grouped and the x pairs and y pairs of the locations are encoded, respectively. Simulation results demonstrate that our method outperforms O'Connell's method. © 2001 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 11, 277–282, 2000     

Improved upsampling filter design for spatially scalable video coding

Scalable video coding is an ongoing standard, and the current working draft (WD) is to be finalized as an extension of H.264/AVC. It provides scalability at the bit stream level with good compression efficiency and allowing free combinations of spatial, temporal and quality scalability. In the WD, a uniform up‐sampling filter is employed to interpolate the base layer frames. This technique achieves high interpolated precision for both luma component and chroma components, but it results in extremely large encoding time which obstructs it from practical use. This paper proposes an improved up‐sampling filter design for spatially scalable video coding. It makes use of a basic characteristic of human vision system and intends to assign different filters for different components. Specifically, current usage of the 6‐tap up‐sampling filter is only for luma component, but for chroma components, much more simplified filter such as 4‐tap filter or 2‐tap filter should be used instead. Experimental results show that improved up‐sampling filter design reduces the computational complexity significantly with negligible coding loss and bit‐rate increases. © 2008 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 17, 315–319, 2007     

Multiscale Galerkin method using interpolation wavelets for two‐dimensional elliptic problems in general domains

One major hurdle in developing an efficient wavelet‐based numerical method is the difficulty in the treatment of general boundaries bounding two‐ or three‐dimensional domains. The objective of this investigation is to develop an adaptive multiscale wavelet‐based numerical method which can handle general boundary conditions along curved boundaries. The multiscale analysis is achieved in a multi‐resolution setting by employing hat interpolation wavelets in the frame of a fictitious domain method. No penalty term or the Lagrange multiplier need to be used in the present formulation. The validity of the proposed method and the effectiveness of the multiscale adaptive scheme are demonstrated by numerical examples dealing with the Dirichlet and Neumann boundary‐value problems in quadrilateral and quarter circular domains. Copyright © 2003 John Wiley & Sons, Ltd.     

A fourth‐order compact scheme for the Helmholtz equation: Alpha‐interpolation of FEM and FDM stencils

We propose a fourth‐order compact scheme on structured meshes for the Helmholtz equation given by R(φ):=f( x )+Δφ+ξ²φ=0. The scheme consists of taking the alpha‐interpolation of the Galerkin finite element method and the classical central finite difference method. In 1D, this scheme is identical to the alpha‐interpolation method (J. Comput. Appl. Math. 1982; 8 (1):15–19) and in 2D making the choice α=0.5 we recover the generalized fourth‐order compact Padé approximation (J. Comput. Phys. 1995; 119 :252–270; Comput. Meth. Appl. Mech. Engrg 1998; 163 :343–358) (therein using the parameter γ=2). We follow (SIAM Rev. 2000; 42 (3):451–484; Comput. Meth. Appl. Mech. Engrg 1995; 128 :325–359) for the analysis of this scheme and its performance on square meshes is compared with that of the quasi‐stabilized FEM (Comput. Meth. Appl. Mech. Engrg 1995; 128 :325–359). In particular, we show that the relative phase error of the numerical solution and the local truncation error of this scheme for plane wave solutions diminish at the rate O((ξ?)⁴), where ξ, ? represent the wavenumber and the mesh size, respectively. An expression for the parameter α is given that minimizes the maximum relative phase error in a sense that will be explained in Section 4.5. Convergence studies of the error in the L² norm, the H¹ semi‐norm and the l^∞ Euclidean norm are done and the pollution effect is found to be small. Copyright © 2010 John Wiley & Sons, Ltd.     

Deterministic Assembly of Flexible Si/Ge Nanoribbons via Edge‐Cutting Transfer and Printing for van der Waals Heterojunctions

As the promising building blocks for flexible electronics and photonics, inorganic semiconductor nanomembranes have attracted considerable attention owing to their excellent mechanical flexibility and electrical/optical properties. To functionalize these building blocks with complex components, transfer and printing methods in a convenient and precise way are urgently demanded. A combined and controllable approach called edge‐cutting transfer method to assemble semiconductor nanoribbons with defined width (down to submicrometer) and length (up to millimeter) is proposed. The transfer efficiency can be comprehended by a classical cantilever model, in which the difference of stress distributions between forth and back edges is investigated using finite element method. In addition, the vertical van der Waals PN (p‐Si/n‐Ge) junction constructed by a two‐round process presents a typical rectifying behavior. The proposed technology may provide a practical, reliable, and cost‐efficient strategy for transfer and printing routines, and thus expediting its potential applications for roll‐to‐roll productions for flexible devices.     

一种均匀线阵互耦校正算法

旋转不变子空间(Estimating Signal Parameters via Rotational Invariance Techniques,ESPRIT)算法是空间谱估计中的典型算法,但是阵列互耦会严重影响ESPRIT算法的测向性能。将均匀线阵划分为冗余阵元和有效中心阵元,对有效中心阵元利用ESPRIT算法估计出校正源方位角,结合冗余阵元信息估计出互耦系数阵。计算机仿真显示该算法在互耦自由度为2或3时均有效,算法还从仿真角度研究了幅度和相位误差对算法性能的影响。该算法校正时只需单个未知方位校正源,是一种操作简单的均匀线阵互耦校正算法。     

POD–ISAT: An efficient POD‐based surrogate approach with adaptive tabulation and fidelity regions for parametrized steady‐state PDE discrete solutions

A combination of proper orthogonal decomposition (POD) analysis and in situ adaptive tabulation (ISAT) is proposed for the representation of parameter‐dependent solutions of coupled partial differential equation problems. POD is used for the low‐order representation of the spatial fields and ISAT for the local representation of the solution in the design parameter space. The accuracy of the method is easily controlled by free threshold parameters that can be adjusted according to user needs. The method is tested on a coupled fluid‐thermal problem: the design of a simplified aircraft air control system. It is successfully compared with the standard POD; although the POD is inaccurate in certain areas of the design parameters space, the POD–ISAT method achieves accuracy thanks to trust regions based on residuals of the fluid‐thermal problem. The presented POD–ISAT approach provides flexibility, robustness and tunable accuracy to represent solutions of parametrized partial differential equations.Copyright © 2013 John Wiley & Sons, Ltd.     

Dispersion error reduction for acoustic problems using the edge‐based smoothed finite element method (ES‐FEM)

The paper reports a detailed analysis on the numerical dispersion error in solving 2D acoustic problems governed by the Helmholtz equation using the edge‐based smoothed finite element method (ES‐FEM), in comparison with the standard FEM. It is found that the dispersion error of the standard FEM for solving acoustic problems is essentially caused by the ‘overly stiff’ feature of the discrete model. In such an ‘overly stiff’ FEM model, the wave propagates with an artificially higher ‘numerical’ speed, and hence the numerical wave‐number becomes significantly smaller than the actual exact one. Owing to the proper softening effects provided naturally by the edge‐based gradient smoothing operations, the ES‐FEM model, however, behaves much softer than the standard FEM model, leading to the so‐called very ‘close‐to‐exact’ stiffness. Therefore the ES‐FEM can naturally and effectively reduce the dispersion error in the numerical solution in solving acoustic problems. Results of both theoretical and numerical studies will support these important findings. It is shown clearly that the ES‐FEM suits ideally well for solving acoustic problems governed by the Helmholtz equations, because of the crucial effectiveness in reducing the dispersion error in the discrete numerical model. Copyright © 2010 John Wiley & Sons, Ltd.     

Fast template matching using correlation‐based adaptive predictive search

We have developed the Correlation‐based Adaptive Predictive Search (CAPS) as a fast search strategy for multidimensional template matching. A 2D template is analyzed, and certain characteristics are computed from its autocorrelation. The extracted information is then used to speed up the search procedure. This method provides a significant improvement in computation time while retaining the accuracy of traditional full‐search matching. We have extended CAPS to three and higher dimensions. An example of the third dimension is rotation where rotated targets can be located while again substantially reducing the computational requirements. CAPS can also be applied in multiple steps to further speed up the template matching process. Experiments were conducted to evaluate the performance of 2D, 3D, and multiple‐step CAPS algorithms. Compared to the conventional full‐search method, we achieved speedup ratios of up to 66.5 and 145 with 2D and 3D CAPS, respectively. © 2003 Wiley Periodicals, Inc. Int J Imaging Syst Technol 13, 169–178, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.10055     

Homogeneous 2D MoTe2 CMOS Inverters and p–n Junctions Formed by Laser‐Irradiation‐Induced p‐Type Doping

Among all typical transition‐metal dichalcogenides (TMDs), the bandgap of α‐MoTe₂ is smallest and is close to that of conventional 3D Si. The properties of α‐MoTe₂ make it a favorable candidate for future electronic devices. Even though there are a few reports regarding fabrication of complementary metal–oxide‐semiconductor (CMOS) inverters or p–n junction by controlling the charge‐carrier polarity of TMDs, the fabrication process is complicated. Here, a straightforward selective doping technique is demonstrated to fabricate a 2D p–n junction diode and CMOS inverter on a single α‐MoTe₂ nanoflake. The n‐doped channel of a single α‐MoTe₂ nanoflake is selectively converted to a p‐doped region via laser‐irradiation‐induced MoO_x doping. The homogeneous 2D MoTe₂ CMOS inverter has a high DC voltage gain of 28, desirable noise margin (NM_H = 0.52 V_DD, NM_L = 0.40 V_DD), and an AC gain of 4 at 10 kHz. The results show that the doping technique by laser scan can be potentially used for future larger‐scale MoTe₂ CMOS circuits.     

彩色输出设备特征化的三维查找表方法

设备的特征化是色彩管理的关键.给出了一种构建常用数字影像硬拷贝输出设备特征化三维查找表的方法.在RGB数字空间中均匀采样,并进行数据的虚拟扩充;经四面体线性插值技术,建立了由CIEL*a*b*到RGB变换的特征化三维查找表.对3种类型6个不同设备的实验表明,四面体线性插值技术同样适于采样数据的虚拟扩充;由扩充后的采样数据得到的33×33×33尺寸的三维查找表,转换色差较使用未扩充的采样数据得到的17×17×17尺寸的查找表有了明显降低.在其中一个输出设备上对实际影像进行了应用,变换后的影像色彩得到有效校正.     

Constraint‐corrected J–R curve based on three‐dimensional finite element analyses

Three‐dimensional (3D) finite element analyses are carried out on single‐edge bend [SE(B)] specimens for which the J‐integral resistance curves (J–R curves) have been experimentally determined to develop the constraint‐corrected J–R curves for the X80 grade pipe steel. The constraint parameters considered in this study include Q_HRR, Q_SSY, Q_{SSY_m}, Q_LM, Q_BM1, Q_BM2, A₂, h and T_z. The constraint‐corrected J–R curves were developed on the basis of the constraint parameters obtained from finite element analysis and experimentally determined J–R curves associated with deeply cracked and medium‐cracked SE(B) specimens and validated against shallow‐cracked SE(B) specimens. The analysis results indicate that all the constraint parameters considered in this study except Q_HRR, Q_SSY, Q_{SSY_m} and Q_LM lead to reasonably accurate constraint‐corrected J–R curves if the crack extensions are relatively small (≤0.7 mm). For larger crack extensions (≤1.5 mm), the Q_BM1‐based constraint‐corrected J–R curve leads to the most accurate predictions of J among all the constraint parameters considered.     

Optimizing the multipole‐to‐local operator in the fast multipole method for graphical processing units

This paper presents a number of algorithms to run the fast multipole method (FMM) on NVIDIA CUDA‐capable graphical processing units (GPUs) (Nvidia Corporation, Sta. Clara, CA, USA). The FMM is a class of methods to compute pairwise interactions between N particles for a given error tolerance and with computational cost of . The methods described in the paper are applicable to any FMMs in which the multipole‐to‐local (M2L) operator is a dense matrix and the matrix is precomputed. This is the case for example in the black‐box fast multipole method (bbFMM), which is a variant of the FMM that can handle large class of kernels. This example will be used in our benchmarks. In the FMM, two operators represent most of the computational cost, and an optimal implementation typically tries to balance those two operators. One is the nearby interaction calculation (direct sum calculation, line 29 in Listing 1), and the other is the M2L operation. We focus on the M2L. By combining multiple M2L operations and reordering the primitive loops of the M2L so that CUDA threads can reuse or share common data, these approaches reduce the movement of data in the GPU. Because memory bandwidth is the primary bottleneck of these methods, significant performance improvements are realized. Four M2L schemes are detailed and analyzed in the case of a uniform tree. The four schemes are tested and compared with an optimized, OpenMP parallelized, multi‐core CPU code. We consider high and low precision calculations by varying the number of Chebyshev nodes used in the bbFMM. The accuracy of the GPU codes is found to be satisfactory and achieved performance over 200 Gflop/s on one NVIDIA Tesla C1060 GPU (Nvidia Corporation, Sta. Clara, CA, USA). This was compared against two quad‐core Intel Xeon E5345 processors (Intel Corporation, Sta. Clara, CA, USA) running at 2.33 GHz, for a combined peak performance of 149 Gflop/s for single precision. For the low FMM accuracy case, the observed performance of the CPU code was 37 Gflop/s, whereas for the high FMM accuracy case, the performance was about 8.5 Gflop/s, most likely because of a higher frequency of cache misses. We also present benchmarks on an NVIDIA C2050 GPU (a Fermi processor)(Nvidia Corporation, Sta. Clara, CA, USA) in single and double precision. Copyright © 2011 John Wiley & Sons, Ltd.