Pupil Effect in a GRIN Lens with Gaussian Illumination

Abstract

Using the propagator method, the quasi-geometric transmittance function and complex amplitude distribution produced by a GRIN lens are evaluated when it is illuminated by a Gaussian beam and the pupil effect is taken into account. The effective pupil is defined and derived by both quasi-geometrical optics and the exact Fresnel diffraction, which it is evaluated in a Rubinowicz representation.     

基于四元数傅里叶变换的彩色图像数字水印算法

目的提高彩色图像数字水印的抗攻击性能,包括缩放、旋转、平移、噪声攻击等。方法基于坐标变换和四元数傅里叶变换提出一种彩色图像数字水印算法。介绍彩色图像四元数表示形式及其双侧傅里叶变换,并分析笛卡尔坐标和极对数坐标之间的变换关系。选择四元数傅里叶变换后实部的中低频部分作为嵌入区域;为提高算法的抗几何攻击能力,给出笛卡尔坐标系和对数极坐标系之间对应点的位置关系;详细论述水印嵌入和提取的流程。结果针对噪声、滤波、剪切等攻击进行了实验研究,结果表明所述算法可以提高提取信息的准确率和水印的抗攻击能力。结论该算法在保证水印隐蔽性的同时能够抵抗一定程度的攻击,满足版权保护和数字防伪的需要。     

FFT谱连续细化分析的富里叶变换法

本文提出了利用富里叶变换对ＦＦＴ谱的局部进行细化分析的方法。在细化频谱分析时，可以得到某个主要频率成份频率、幅值、相位的精确值，极大地提高频率分辨力，对瞬态及恒定采样长度信号的频率细化分析十分有效。     

利用灰度图提高Fourier变换轮廓术的测量精度

在ＦＴＰ测量中,常利用π相移方法来消除零频,以避免谱频混叠,提高ＦＴＰ的测量精度。此时,测量系统中包含相移装置,增加了系统的复杂性。然而,人们常常忽略了灰度图中包含的信息在ＦＴＰ测量中的作用。本文提出了在ＦＴＰ测量中利用一帧灰度图来提高测量精度的方法,该方法测量装置简单,又可以达到π相移的效果,在实际的ＦＴＰ测量中的意义。     

浅谈镜头焦距技术对画面造型的影响

光学镜头在影视作品的摄制中，对画面的造型有着至关重要的影响，所以摄影师应对光学镜头的有关术语、不同焦距镜头的光学特性、造型性能及镜头焦距技术的应用有深入的了解。本文就以上问题做一粗浅的探讨。     

Linear Bijections and the Fast Fourier Transform

 Fast Fourier transform algorithms rely upon the choice of certain bijective mappings between the indices of the data arrays. The two basic mappings used in the literature lead to Cooley–Tukey algorithms or to prime factor algorithms. But many other bijections also lead to FFT algorithms, and a complete classification of these mappings is provided. One particular choice leads to a new FFT algorithm that generalizes the prime factor algorithm. It has the advantage of reducing the floating point operation count by reducing the number of trigonometric function evaluations. A certain equivalence relation is defined on the set of bijections that lead to FFT algorithms, and its connection with isomorphism classes of group extensions is studied. Under this equivalence relation every equivalence class contains bijections leading to an FFT algorithm of the new type. Received October 27, 1994; revised version January 25, 1996     

基于傅里叶变换的微结构全彩色三维面形重构

分析表明,在傅里叶成像光谱仪的干涉信号中,不仅含有光谱信息,同样也包含三维面形结构信息。因此,本文基于傅里叶变换光谱技术,提出一种彩色三维面形检测方法,不仅可以测量物体表面各个点的光谱反射率分布,还可以获得物体表面三维面形数据,达到三维面形超光谱成像。通过纹理映射将光谱像和三维面形相融合,实现了微结构彩色物体全彩色三维面形数字重构。     

General Implementation of the Incoherent Optical Fourier Transform by Interference

Abstract

The possibility of performing an incoherent optical Fourier transform with interferometers comprising two arms optically centred on the same axis has been investigated. Any interferometer of this type is suitable provided two conditions are met: the centre of the source should be imaged through both arms onto the same point, and the centre of the observation plane should be the image through both arms of the same point. One possible experimental set-up is introduced and results are presented.     

Transient Deformation Measurement by Double-Pulsed-Subtraction TV Holography and the Fourier Transform Method

We report the measurement of transient bending waves with double-pulsed-subtraction TV holography. The correlation fringe patterns are automatically quantitatively analyzed by the application of Fourier methods. A novel optical setup with two different object-beam optical paths is demonstrated for the generation of carrier fringes. The proposed system is highly immune to environmental disturbances because the optical setup imposes no lower limit on the time separation between laser pulses. One removes the linear phase distribution due to the spatial carrier in the spatial domain by subtracting the phase of the undeformed carrier fringes from the phase of the modulated fringes. Experimental results obtained with an aluminum plate excited by the impact of a piezoelectric translator are presented.     

Image Formation by Magneto-optic Effects

The observation of magnetic domain structures by means of the Faraday and Kerr effect is described in terms of geometrical and physical optics; experimental techniques and theoretical explanations depend on the magnetic and optical properties of the investigated materials. Two methods are presented considering magnetization objects by means of Kirchhoff's diffraction theory. Starting from the calculation of intensities and polarization states of the diffraction by a magnetization grating, experiments are discussed concerning Fraunhofer diffraction and dark-field observation, artefacts in the image of domains, multiple diffraction by thick specimens, object functions available by magnetic structures and the applications for the investigation of magnetization reversal processes and data processing.     

Effect of ultrasound on the setting characteristics of glass ionomer cements studied by Fourier Transform Infrared Spectroscopy

OBJECTIVE: To investigate the effect of ultrasound (US) application, US staring time and US duration on the setting of glass ionomer cement (GIC) by using Attenuated Total Reflectance Fourier Transform Infrared (ATR/FTIR) spectrometer. METHODS: Two conventional GICs, Fuji IX Fast and Ketac Molar were studied. US application was started at 30 s or 40 s after mixing and was applied for times between 15 and 55 s on samples of two different thicknesses. The samples were analysed using ATR/FTIR. RESULTS: US accelerated the curing process in both cements, US needed to be applied for more than 15 s. Both Fuji IX and Ketac Molar showed increased setting on increasing the US application duration from 15 s to 55 s. Increased setting of the GICs was produced when US application started 40 s after mixing rather than 30 s after mixing. CONCLUSIONS: The significant findings of the study include that US application accelerated the setting processes, by accelerating the formation of the acid salts. The salt formation increased with increase time of US application. The effect of application of US to setting GICs is influenced by time of the start of application of the US. The effects appear to material specific, with Ketac Molar showing a greater effect than Fuji IX.     

Complete Isochromatic Fringe-order Analysis in Digital Photoelasticity by Fourier Transform and Load Stepping

Abstract:  In this paper, a new fully automated photoelastic technique based on both the Fourier transform and the envelope of the fringe centres, is presented. Using two images of the isochromatics acquired with different loads and a simple calculation routine, the method allows the user the complete determination of the isochromatic fringe retardation on any arbitrary line chosen over the model domain, without the need for supplementary external information or calibration. Various experiments have corroborated the accuracy of the method, estimated theoretically to about 0.07 fringe orders. As a result of its simplicity and sufficient accuracy, the method can be used in the industrial field also by a non-expert user.     

傅里叶变换轮廓术测量方法的分析研究

对传统傅里叶变换轮廓术（FTP)、π相移法以及灰度图法测量结果进行对比分析。结果证明,随着被测物体高度梯度的增加,基于灰度图和π相移技术的改进傅里叶变换轮廓术取得了很好效果,特别是在梯度大于3的情况下适合采用π相移法,能更有效地提高傅里叶变换轮廓术的测量精度。     

数字脊波变换及图像的稀疏表示

在二维或更高维空间中,小波不能有效地表达沿边缘间断的物体。脊波变换对连续空间中沿直线奇异的函数能够进行稀疏表达。理论上的吸引力促使人们将其从连续概念转化到数字实现。本文着重比较脊波变换的几种不同数字实现及对于小波的改进。实验结果说明,脊波在对具有直线边缘的图像逼近和去噪时的确比小波有效。     

氟化非晶碳膜结构的Raman和FTIR研究

利用反应射频磁控溅射法,以单晶Si片为衬底,在不同功率下制备了氟化非晶碳膜样品,并进行了不同温度的退火处理。采用拉曼光谱、傅里叶变换红外光谱和原子力显微镜对样品的结构进行了表征。通过谱线Lorentzian分峰拟合方法,分析比较了不同功率下制备的氟化非晶碳膜sp杂化结构,得到了薄膜生长过程功率控制与结构的关系,功率增大、退火温度升高,膜内sp2相对含量增加。退火温度达到350℃时,薄膜中石墨结构明显增加。     

Time-Resolved Electrochemical Impedance Spectroscopy of Stochastic Nanoparticle Collision: Short Time Fourier Transform versus Continuous Wavelet Transform

This work demonstrates the utilization of short-time Fourier transform (STFT), and continuous wavelet transform (CWT) electrochemical impedance spectroscopy (EIS) for time-resolved analysis of stochastic collision events of platinum nanoparticles (NPs) onto gold ultramicroelectrode (UME). The enhanced electrocatalytic activity is observed in both chronoamperometry (CA) and EIS. CA provides the impact moment and rough estimation of the size of NPs. The quantitative information such as charge transfer resistance (R_ct) relevant to the exchange current density of a single Pt NP is estimated from EIS. The CWT analysis of the phase angle parameter is better for NP collision detection in terms of time resolution compared to the STFT method.     

短时傅里叶变换的FPGA实现及其应用

针对机械设备实时监控中信号处理的需要,在研究短时傅里叶变换Goertzel递推算法与该算法滤波器结构的基础上,提出一种基于FPGA（Field-Programmable Gate Array：现场可编程门阵列）的短时傅里叶变换实现方案,该方案充分利用FPGA嵌入式RAM资源、嵌入式乘法器及其灵活的IP Core功能。通过对仿真信号与实际工程信号的测试,验证了该方案的正确性。     

傅里叶变换轮廓术中三维坐标同时校准方法

在相位测量型光学三维面形测量中,最终都要将相位信息转换成被测物体的高度分布信息,这个过程往往是通过对已知世界空间坐标的特征点事先标定,获得测量系统的内外特征参数后,完成被测物体的三维坐标转换.因此,标定是三维面形测量的关键环节.本文基于双向二次相位-高度映射方法和摄像机针孔模型线性无畸变标定技术,充分利用傅里叶变换的频谱方向特性,提出了对含有特征点的二维标定物表面变形条纹的频谱进行方向滤波操作,同时获取测量系统XYZ三个方向上的标定数据,对测量系统进行立体校准的系统标定方法.结合旋转风扇叶片形变的测量系统,给出了该方法的标定结果:在XY面内(230mm×230mm)的标准偏差小于0.27mm;在Z方向上小于0.022mm,位移测量灵敏度优于0.05mm.该方法为测量系统的实用化奠定了基础.