Manipulations of chaotic and ghost images for non-local information retrieval

We present experiments of χ ⁽²⁾ difference-frequency processes at frequency degeneracy in regime of high intensity. In the first experiment, we exploit ghost-imaging in the context of quantum cryptography in an attempt to overcome the limitation of the quantum key distribution of keys as long as the image. The code to be encrypted is the string of the power values measured by Alice in the test arm. In the second experiment, we generate frequency down-converted images that are chaotic as, at each laser shot, both the field at 2ω illuminating the object to be imaged and the seed-field at ω are made pseudo-thermal in space. The images are recovered from the recorded chaotic ones by correlating the local intensity fluctuations with those of the seed-field Fourier components. Calculating the correlations in parallel with many Fourier components allows image retrieval by averaging on ensembles of fewer recorded images. The text was submitted by the authors in English.     

Chaotic imaging in frequency downconversion

We analyze and recover, by means of spatial intensity correlations, the image obtained by a seeded frequency-downconversion process in which the seed field is chaotic and an intensity modulation is encoded in the pump field. Although the field generated is as chaotic as the seed field and does not carry any information about the modulation of the pump, one can extract an image of the pump by measuring the spatial intensity correlations between the generated field and one Fourier component of the seed.     

Fusion of infrared polarization and intensity images using support value transform and fuzzy combination rules

Infrared polarization and intensity imagery provide complementary and discriminative information in image understanding and interpretation. In this paper, a novel fusion method is proposed by effectively merging the information with various combination rules. It makes use of both low-frequency and high-frequency images components from support value transform (SVT), and applies fuzzy logic in the combination process. Images (both infrared polarization and intensity images) to be fused are firstly decomposed into low-frequency component images and support value image sequences by the SVT. Then the low-frequency component images are combined using a fuzzy combination rule blending three sub-combination methods of (1) region feature maximum, (2) region feature weighting average, and (3) pixel value maximum; and the support value image sequences are merged using a fuzzy combination rule fusing two sub-combination methods of (1) pixel energy maximum and (2) region feature weighting. With the variables of two newly defined features, i.e. the low-frequency difference feature for low-frequency component images and the support-value difference feature for support value image sequences, trapezoidal membership functions are proposed and developed in tuning the fuzzy fusion process. Finally the fused image is obtained by inverse SVT operations. Experimental results of visual inspection and quantitative evaluation both indicate the superiority of the proposed method to its counterparts in image fusion of infrared polarization and intensity images.     

Fluorescence lifetime imaging of intracellular calcium

Fluorescence lifetime imaging microscopy (FLIM) is a new methodology for studying the spatial and temporal dynamics of macromolecule, molecules, and ions in living cells. In FLIM image contrast is derived from the mean fluorescence lifetime at each point in a two-dimensional image. In our case the lifetime was measured by the phase-modulation method. We describe our FLIM apparatus, which consists of a fluorescence microscope, high-speed gated proximity focused MCP image intensifier, and slow-scan CCD camera. To accomplish subnanosecond time-resolved imaging, the gain of the image intensifier is modulated with a high-frequency signal, resulting in stationary phase-sensitive intensity images on the image intensifier. These images are recorded using a cooled slow-scan CCD camera and stored in an image processor. The lifetime images are created from a series of phase-sensitive images at various phase shift of the gain-modulation signal. We demonstrate calcium concentration imaging in living COS cells based on Ca²⁺-induced lifetime changes of Quin-2. The phase-angle image is mapped to the Ca²⁺ concentration image using anin vitro-determined calibration curve. The Ca²⁺ concentration was found to be uniform throughout the cell. In contrast, the intensity image shows significant spatial differences, which likely reflect variations in the thickness and distribution of probe within the cell.     

An energy minimization method for MS lesion segmentation from T1-w and FLAIR images

In this paper, we extend the multiplicative intrinsic component optimization (MICO) algorithm to multichannel MR image segmentation, with focus on segmentation of multiple sclerosis (MS) lesions. The MICO algorithm was originally proposed by Li et al. in Ref. [1] for normal brain tissue segmentation and intensity inhomogeneity correction of a single channel MR image, which exhibits desirable advantages over other methods for MR image segmentation and intensity inhomogeneity correction in terms of segmentation accuracy and robustness. In this paper, we extend the MICO algorithm to multi-channel MR image segmentation and enable the segmentation of MS lesions. We assign different weights for different channels to control the impact of each channel. The weighted channels allow the enhancement of the impact of the FLAIR image on the segmentation of MS lesions by assigning a larger weight to the FLAIR image channel than the other channels. With the inherent mechanism of estimation of the bias field, our method is able to deal with the intensity inhomogeneity in the input multi-channel MR images. In the application of our method, we only use T1-w and FLAIR images as the input two channel MR images. Experimental results show promising result of our method.     

Three-dimensional temperature measurement in turbulent thermal convection by extended range scanning liquid crystal thermometry

The usable temperature range of liquid crystal thermometry has been extended and used to measure three-dimensional temperature fields in turbulent thermal convection. The color of the liquid crystals is calibrated against temperature using the standard method in which hue is the single input variable and two new methods: hue/intensity as input variable, and hue, saturation and intensity as input variables to a neural network. Relative to the hue calibration, the new methods extend the range over which temperature can be measured by more than 100%. Three-dimensional temperature measurements of turbulent thermal convection over smooth surfaces were carried out at a flux Rayleigh number of 3 × 10⁹ by scanning a white light sheet normal to the visualized image plane and capturing a number of sequential images at various positions of the light sheet. Stacks of the planar data were composed into three-dimensional temperature distributions. The results indicate the presence of an irregular spoke pattern over the surface and the generation of plumes from the intersections of the patterns, consistent with other investigations.     

Secret Communication Systems Using Chaotic Wave Equations with Neural Network Boundary Conditions

In a secret communication system using chaotic synchronization, the communication information is embedded in a signal that behaves as chaos and is sent to the receiver to retrieve the information. In a previous study, a chaotic synchronous system was developed by integrating the wave equation with the van der Pol boundary condition, of which the number of the parameters are only three, which is not enough for security. In this study, we replace the nonlinear boundary condition with an artificial neural network, thereby making the transmitted information difficult to leak. The neural network is divided into two parts; the first half is used as the left boundary condition of the wave equation and the second half is used as that on the right boundary, thus replacing the original nonlinear boundary condition. We also show the results for both monochrome and color images and evaluate the security performance. In particular, it is shown that the encrypted images are almost identical regardless of the input images. The learning performance of the neural network is also investigated. The calculated Lyapunov exponent shows that the learned neural network causes some chaotic vibration effect. The information in the original image is completely invisible when viewed through the image obtained after being concealed by the proposed system. Some security tests are also performed. The proposed method is designed in such a way that the transmitted images are encrypted into almost identical images of waves, thereby preventing the retrieval of information from the original image. The numerical results show that the encrypted images are certainly almost identical, which supports the security of the proposed method. Some security tests are also performed. The proposed method is designed in such a way that the transmitted images are encrypted into almost identical images of waves, thereby preventing the retrieval of information from the original image. The numerical results show that the encrypted images are certainly almost identical, which supports the security of the proposed method.     

基于支持度变换和top-hat分解的双色中波红外图像融合

为了解决用多尺度top-hat分解法融合双色中波红外图像时经常存在对比度提升有限、边缘区域失真较重的问题,提出了基于支持度变换和top-hat分解相结合的融合方法。先用支持度变换法将双色中波图像分解为低频图像和支持度图像序列;再从最后一层低频图像中用多尺度top-hat分解法提取各自的亮信息和暗信息;用灰度值取大法分别融合亮信息和暗信息;通过灰度值归一化和高斯滤波分别增强亮、暗信息融合图像;然后融合两低频图像和亮、暗信息增强图像;将融合图像作为新的低频图像和用灰度值取大法融合得到的支持度融合图像序列进行支持度逆变换,得到最终融合图像。该方法的实验结果同采用单一的支持度变换法融合和多尺度top-hat分解法融合相比,融合图像的对比度提升了11.69%,失真度降低了63.42%,局部粗糙度提高了38.12%。说明提出的从低频图像提取亮暗信息,并经过分别融合、增强,再与低频图像进行融合,能有效破解红外融合图像对比度提升和边缘区域失真度降低之间的矛盾,为提高图像融合质量提供了新方法。     

Digital chaotic sequence generator based on coupled chaotic systems

Chaotic systems perform well as a new rich source of cryptography and pseudo-random coding. Unfortunately their digital dynamical properties would degrade due to the finite computing precision. Proposed in this paper is a modified digital chaotic sequence generator based on chaotic logistic systems with a coupling structure where one chaotic subsystem generates perturbation signals to disturb the control parameter of the other one. The numerical simulations show that the length of chaotic orbits, the output distribution of chaotic system, and the security of chaotic sequences have been greatly improved. Moreover the chaotic sequence period can be extended at least by one order of magnitude longer than that of the uncoupled logistic system and the difficulty in decrypting increases 2¹²⁸*2¹²⁸ times indicating that the dynamical degradation of digital chaos is effectively improved. A field programmable gate array (FPGA) implementation of an algorithm is given and the corresponding experiment shows that the output speed of the generated chaotic sequences can reach 571.4~Mbps indicating that the designed generator can be applied to the real-time video image encryption.     

Image Security Based on Three-Dimensional Chaotic System and Random Dynamic Selection

Image encryption based on a chaos system can effectively protect the privacy of digital images. It is said that a 3D chaotic system has a larger parameter range, better unpredictability and more complex behavior compared to low-dimension chaotic systems. Motivated by this fact, we propose a new image cryptosystem that makes use of a 3D chaotic system. There are three main steps in our scheme. In the first step, the chaotic system uses the hash value of the plaintext image to generate three sequences. In step two, one of the sequences is used to dynamically select confusion and diffusion methods, where confusion and diffusion have three algorithms, respectively, and will produce 3²ⁿ (n > 100) combinations for encryption. In step three, the image is divided into hundreds of overlapping subblocks, along with the other two sequences, and each block is encrypted in the confusion and diffusion process. Information entropy, NPCR, UACI results and various security analysis results show that the algorithm has a better security performance than existing, similar algorithms, and can better resist clipping, noise, statistical analysis and other attacks.     

Light-induced damage mechanisms in α-phase proton-exchanged LiNbO3 waveguides

The overall power and far-field pattern of the beam out-coupled from a single-mode planar proton-exchanged LiNbO₃ waveguide in the α-phase have been studied for in-coupled intensities within the range 20–700 W/cm². The steady-state output versus input power response shows three definite stages designated as I, II, and III in order of increasing input intensity. In stage I the output varies linearly with input and the far-field pattern does not show appreciable changes. In stage II, the pattern is considerably broadened and displays a number of steady peaks and dips indicative of a filamentary structure of the beam. As in bulk LiNbO₃, these damage features are explained in terms of parametric processes involving the amplification of scattered (noise) light. An additional broadening is observed in stage III together with the occurrence of a fluctuating profile (chaotic response) attributed to random fluctuations in the coupling parameters. The threshold input intensity separating stages I and II is related to the intensity-dependence of the photovoltaic field. Received: 18 November 1998 / Revised version: 13 January 1999 / Published online: 12 April 1999     

The magnetic field dependence of the breathing artifact

Breathing causes ghost artifacts in magnetic resonance (MR) images. These ghosts are more conspicuous at high magnetic field strength due to (i) operational factors that affect the relative intensity of the individual ghosts and (ii) factors that affect the image intensity of the moving structures producing the ghosts. Both types of factors are identified and illustrated with images of a human subject. A brief theoretical analysis of the noiseless MR image of a point object in sinusoidal motion shows that the intensity structure of each ghost depends on the number of pixels over which the object moves. Generally, images with narrower pixels have ghosts with greater relative intensity. However, the breathing artifact is more apparent at high magnetic field strength primarily because the signal-to-noise ratio and the cotnrast between fat and muscle tissues are increased.     

Optical image encryption using improper Hartley transforms and chaos

We propose a new method for image encryption using improper Hartley transform and chaos theory. Improper Hartley transform is a Hartley transform in which the phase between the two Fourier transforms is a fractional multiple of π/2. This fractional order is called fractional parameter and serves as a key in the image encryption and decryption process. Four types of chaos functions have been used. These functions are the logistic map, the tent map, the Kaplan-Yorke map and the Ikeda map. Random intensity masks have been generated using these chaotic functions and are called chaotic random intensity masks. The image is encrypted by using improper Hartley transform and two chaotic random intensity masks. The mean square error has been calculated. The robustness of the proposed technique in terms of blind decryption has been tested. The computer simulations are presented to verify the validity of the proposed technique.     

基于光场成像原理和混沌系统的多图像加密方法

针对现有光学加密方法对加密系统要求高、受器件性能限制、加密效率低、解密图像易失真的局限性,提出一种基于光场成像原理和混沌系统的多图像加密方法.该方法利用混沌系统随机生成光场成像系统的个数与系统参数,并在计算机中构造出相应的多个光场成像系统;将多幅待加密图像拼接后置于光场成像系统中依次计算得到光场图像,通过提取光场图像的多幅子孔径图像并进行拼接,实现多幅图像的快速加密.解密过程为加密过程的逆过程.该方法将计算成像的方式引入加密过程,使加密不受硬件条件的限制,易于实现.实验结果表明,提出的算法密钥复杂度低,易于传输;对噪声有较好的鲁棒性,密钥空间大,密钥敏感度高,安全性好;加密效率高,解密图像无损失.在需要大量图像进行安全传输的领域具有广泛的应用前景.     

Distribution of anomalous exponents of natural images

Recent studies of correlations of intensity in databases of natural images revealed a remarkable property. The two point correlations are described in terms of power law behavior, with an exponent which seems to be robust. In the present Letter we consider the statistical meaning of that result. We study many individual images of one of the databases considered. We find that the same law characterizing the correlations in the whole database governs also images randomly chosen from that database, with one essential difference. The exponent characterizing each image is specific and differs from the exponent characterizing the whole database. The distribution of single image exponents has been measured and found to exhibit a rather heavy tail. The database exponent cannot, thus, be considered as a statistical representative of a single image exponent. Possible reasons for the diversity in image exponents are discussed.     

High-frequency electromagnon in GdMnO<Subscript>3</Subscript>

Results of far-infrared transmittance are reported for GdMnO₃, a multiferroic perovskite manganite. The spectra allow to obtain position and intensity of the high-frequency electromagnon (~75 cm^-1) in this material. We present a comparative analysis of the high- and low-frequency electromagnons across the phase diagram of GdMnO₃. The traces of the electromagnon excitation can be detected even deeply in the paramagnetic state, which is attributed to magnetic fluctuations.     

Simultaneous Determination of the Amplitude-Phase Structure of an Optical Signal and a Transfer Function with the Influence of the Medium Given by a Modulation Function

We consider a solution to the phase problem in optics as applied to registering and analyzing amplitude-phase structures of 1) d optical fields that form or transfer images and 2) transfer or spread functions of the medium where optically inhomogeneous fields propagate or those of the systems forming fields and producing distortions. The influence of the medium is characterized by the modulation function and is described by the operation of multiplication. In order to measure the amplitude and phase field characteristics and transfer or spread functions, we use an original development of the modulation-spectral method proposed earlier by the authors. There are two variants of optical schemes considered. They include identical parts designed to form the light field to be processed. Using the first optical system, one forms the spectrum of spatial frequencies and introduces the first additional space modulation in the plane of spatial frequencies. The second optical system is placed in the same plane to form the image of the investigated field in the input plane of the developing scheme after passing the transmitting medium. In the first variant, the second part of the scheme contains at the input the third optical system forming the spatial spectrum in the registration plane. At the input of this scheme, the second additional spatial modulation is introduced. In the second variant, the third optical system forms the image of the developing scheme input plane in the registration plane. The second additional spatial modulator is placed in the spatial frequency plane of the third optical system. In the output, in both cases four independent two-dimensional intensity distributions are registered, which allow one to solve the formulated problem.     

Characterizing the relative role of low-frequency and turbulent processes in the nocturnal boundary layer through the analysis of two-point correlations of the wind components

The study presents an analysis of two-point correlations between time series of nocturnal atmospheric wind, obtained from two micrometeorological towers, 45 m horizontally apart, each equipped with two sonic anemometers, 2.5 m vertically apart. It focuses on the scale dependence of the two-point correlations obtained from sensors vertically and horizontally separated. In particular, the role of low-frequency non-turbulent processes in the correlations is assessed, and compared to that of the turbulent scales of motion. The vertical correlations of the streamwise and vertical wind components show little dependence on the turbulence intensity, but those of the spanwise component decrease appreciably as it gets more turbulent. Multiresolution decomposition shows that the two-point correlations become increasingly dominated by low-frequency scales as it gets less turbulent, and that such large-scale processes are largely reduced in fully turbulent conditions. It is also shown that the vertical correlations of the spanwise wind component is negative for very small time scales. Horizontal two-point correlations obtained at the 45 m separation distance between the towers are almost entirely dominated by low-frequency motions, regardless of the turbulence intensity, but the magnitude of such correlations decreases with increasing turbulence intensity for any wind components. A comparison between the horizontal two-point correlations and autocorrelations taken with a time lag given by the ratio of the horizontal separation to the mean wind component in the direction that connects the two towers leads to the conclusion that the statistical properties of turbulence are often preserved over the horizontal distance, despite the lack of turbulence correlations for that separation.     

A robust and secure chaotic standard map based pseudorandom permutation-substitution scheme for image encryption

A novel and robust chaos-based pseudorandom permutation-substitution scheme for image encryption is proposed. It is a loss-less symmetric block cipher and specifically designed for the color images but may also be used for the gray scale images. A secret key of 161-bit, comprising of the initial conditions and system parameter of the chaotic map (the standard map), number of iterations and number of rounds, is used in the algorithm. The whole encryption process is the sequential execution of a preliminary permutation and a fix number of rounds (as specified in the secret key) of substitution and main permutation of the 2D matrix obtained from the 3D image matrix. To increase the speed of encryption all three processes: preliminary permutation, substitution and main permutation are done row-by-row and column-by-column instead of pixel-by-pixel. All the permutation processes are made dependent on the input image matrix and controlled through the pseudo random number sequences (PRNS) generated from the discretization of chaotic standard map which result in both key sensitivity and plaintext sensitivity. However each substitution process is initiated with the initial vectors (different for rows and columns) generated using the secret key and chaotic standard map and then the properties of rows and column pixels of input matrix are mixed with the PRNS generated from the standard map. The security and performance analysis of the proposed image encryption has been performed using the histograms, correlation coefficients, information entropy, key sensitivity analysis, differential analysis, key space analysis, encryption/decryption rate analysis etc. Results suggest that the proposed image encryption technique is robust and secure and can be used for the secure image and video communication applications.     

Multiple-image encryption with bit-plane decomposition and chaotic maps

Image encryption is an efficient technique of image content protection. In this work, we propose a useful image encryption algorithm for multiple grayscale images. The proposed algorithm decomposes input images into bit-planes, randomly swaps bit-blocks among different bit-planes, and conducts XOR operation between the scrambled images and secret matrix controlled by chaotic map. Finally, an encrypted PNG image is obtained by viewing four scrambled grayscale images as its red, green, blue and alpha components. Many simulations are done to illustrate efficiency of our algorithm.