Shot-noise influence on the reconstructed phase image signal-to-noise ratio in digital holographic microscopy

In digital holographic microscopy, shot noise is an intrinsic part of the recording process with the digital camera. We present a study based on simulations and real measurements describing the shot-noise influence in the quality of the reconstructed phase images. Different configurations of the reference wave and the object wave intensities will be discussed, illustrating the detection limit and the coherent amplification of the object wave. The signal-to-noise ratio (SNR) calculation of the reconstructed phase images based on the decision statistical theory is derived from a model for image quality estimation proposed by Wagner and Brown [Phys. Med. Biol. 30, 489 (1985)]. It will be shown that a phase image with a SNR above 10 can be obtained with a mean intensity lower than 10 photons per pixel and per hologram coming from the observed object. Experimental measurements on a glass-chrome probe will be presented to illustrate the main results of the simulations.     

Color image security system using double random-structured phase encoding in gyrator transform domain

A novel method for encoding color information based on a double random phase mask and a double structured phase mask in a gyrator transform domain is proposed. The amplitude transmittance of the Fresnel zone plate is used as structured phase-mask encoding. A color image is first segregated into red, green, and blue component images. Each of these component images are then independently encrypted using first a random phase mask placed at the image plane and transmitted through the first structured phase mask. They are then encoded by the first gyrator transform. The resulting information is again encrypted by a second random phase mask placed at the gyrator transform plane and transmitted through the second structured phase mask, and then encoded by the second gyrator transform. The system parameters of the structured phase mask and gyrator transform in each channel serve as additional encryption keys and enlarge the key space. The encryption process can be realized with an electro-optical hybrid system. The proposed system avoids problems arising from misalignment and benefits of a higher space-bandwidth product. Numerical simulations are presented to confirm the security, validity, and possibility of the proposed idea.     

AFM image reconstruction for deformation measurements by digital image correlation

The scanner drift of the atomic force microscope (AFM) is a great disadvantage to the application of digital image correlation to micro/nano-scale deformation measurements. This paper has addressed the image distortion induced by the scanner drifts and developed a method to reconstruct AFM images for the successful use of AFM image correlation. It?presents such a method, that is to generate a corrected image from two correlated AFM images scanned at the angle of 0° and 90° respectively. The proposed method has been validated by the zero-deformation test. A buckling test of a thin plate under AFM has also been demonstrated. The in-plane displacement field at the centre point of the buckling plate has been successfully characterized by the application of the image correlation technique on reconstructed AFM images.     

Point-spread function synthesis in scanning holographic microscopy

Scanning holographic microscopy is a two-pupil synthesis method allowing the capture of single-sideband in-line holograms of noncoherent (e.g., fluorescent) three-dimensional specimens in a single two-dimensional scan. The flexibility offered by the two-pupil method in synthesizing unusual point-spread functions is discussed. We illustrate and compare three examples of holographic recording, using computer simulations. The first example is the classical hologram in which each object point is encoded as a spherical wave. The second example uses pupils with spherical phase distributions having opposite curvatures, leading to reconstructed images with a resolution limit that is half that of the objective. In the third example, axicon pupils are used to obtain axially sectioned images.     

Single beam two-views holographic particle image velocimetry

Holographic particle image velocimetry (HPIV) is presently the only method that can measure at high resolution all three components of the velocity in a finite volume. In systems that are based on recording one hologram, velocity components parallel to the hologram can be measured throughout the sample volume, but elongation of the particle traces in the depth direction severely limits the accuracy of the velocity component that is perpendicular to the hologram. Previous studies overcame this limitation by simultaneously recording two orthogonal holograms, which inherently required four windows and two recording systems. This paper introduces a technique that maintains the advantages of recording two orthogonal views, but requires only one window and one recording system. Furthermore, it enables a quadruple increase in the spatial resolution. This method is based on placing a mirror in the test section that reflects the object beam at an angle of 45 degrees. Particles located in the volume in which the incident and reflected beams from the mirror overlap are illuminated twice in perpendicular directions. Both views are recorded on the same hologram. Off-axis holography with conjugate reconstruction and high-pass filtering is used for recording and analyzing the holograms. Calibration tests show that two views reduce the uncertainty in the three-dimensional (3-D) coordinates of the particle centroids to within a few microns. The velocity is still determined plane-by-plane by use of two-dimensional particle image velocimetry procedures, but the images are filtered to trim the elongated traces based on the 3-D location of the particle. Consequently, the spatial resolution is quadrupled. Sample data containing more than 200 particles/mm3 are used for calculating the 3-D velocity distributions with interrogation volumes of 220 x 154 x 250 microm, and vector spacing of 110 x 77 x 250 microm. Uncertainty in velocity is addressed by examining how well the data satisfies the continuity equation. The results show significant improvements compared with previous procedures. Limitations of the technique are also discussed.     

Achromatized transmission-type holographic screen for a multiview stereoscopic image system

The main drawback of the use of transmission-type holographic screens is poor color reproduction caused by their high spectral dispersion. For overcoming this drawback, a long, narrow diffusing slit is used as an object when recording the screen. The necessary size and position of the slit relative to the photoplate and to the recording and reconstruction beams are determined by the phase relations of the beams. By use of the slit, holographic screens of 30 cm x 40 cm are recorded with a diverging reference beam and are used to display a multiview full-color stereoscopic image. The images displayed on the screen show no sign of color separation except near the edges of the screen. The image brightness on the screen is high enough that it can be watched in a normally illuminated room.     

采用图像格式的IDE硬盘直写记录

介绍一种采用IDE硬盘的高速图像记录系统的设计方法。该方法去掉了大量的软件编程代 之以硬盘直写图像文件的模式,将图像数据记录到硬盘的同时直接以文件形式存放。实验效果表明,采用该设计方法的记录设备做到了记录完全脱机,事后将硬盘通过USB接口直接与计算机相连,即可对图像进行访问,达到了预期的目的。     

Investigation of the Cauchy-Riemann equations for one-dimensional image recovery in intensity interferometry

A method of image recovery using noniterative phase retrieval is proposed and investigated by simulation. This method adapts the Cauchy-Riemann equations to evaluate derivatives of phase based on derivatives of magnitude. The noise sensitivity of the approach is reduced by employing a least-mean-squares fit. This method uses the analytic properties of the Fourier transform of an object, the magnitude of which is measured with an intensity interferometer. The solution exhibits the degree of nonuniqueness expected from root-flipping arguments for the one-dimensional case, but a simple assumption that restricts translational ambiguity also restricts the space of solutions and permits essentially perfect reconstructions for a number of non-symmetric one-dimensional objects of interest. Very good reconstructions are obtained for a large fraction of random objects, within an overall image flip, which may be acceptable in many applications. Results for the retrieved phase and recovered images are presented for some one-dimensional objects and for different noise levels. Extensions to objects of two dimensions are discussed. Requirements for signal-to-noise ratio are derived for intensity interferometry with use of the proposed processing.     

Holographic zone plates for f x theta and collimating lenses

A holographic zone plate generated by subtracting the spherical wave phase is proposed, that is, a hologram generated by using two divergent or convergent spherical waves. This holographic zone plate can correct the increase in focal power in a radial direction in contrast with the interferometric zone plate. Use of this holographic zone plate for f x O and collimating lenses is analyzed. For an f x O lens, it is shown that an optimum combination of recording spherical waves exists that satisfies both scan linearity and image field flatness. For a collimating lens for a laser diode, it is shown that aberration can be corrected for different playback wavelengths from that used during recording.     

Photosensitive element for an infrared-to-visible image converter

We show that gels can be used to record images formed by IR radiation (in the 10.6-μm wavelength) and then be played back in the visible by a dark-background-illumination technique. The recording process is transient.     

Evolution of the partial image velocimetry measuring technique

Evolution of the non-intrusive flow measuring technique known as particle image velocimetry (PIV) is reviewed. Techniques for illuminating the flow field and recording the images are compared and the principles of image analysis outlined. Recent developments in stereoscopic and holographic PIV, application to vibration fields and fibre optic beam transmission are also discussed.     

Magneto-optical disk drive technology using multiple fiber-coupled flying optical heads. Part II. Laser noise considerations

A magneto-optical data storage system utilizing single-mode fiber is capable of providing high signal-to-noise ratio (SNR) recording if laser noise sources are properly managed. In particular, mode partition noise (MPN) associated with use of a Fabry-Perot laser diode can be a significant problem in a fiber-based system. The various mechanisms leading to MPN as well as to laser phase noise are discussed in the context of a system constructed with polarization-maintaining fiber. The primary noise mechanisms include spurious fiber-endface reflections and errors in the quarter-wave plate on the recording head. An understanding of these effects is essential for fabrication of a fiber-based recording system with suitable SNR performance.     

Contact electron micrography for characterization of paper in a transmission electron microscope: a new technique

Modern electron microscopes are usually fitted with a plate camera system for recording high-resolution electron micrographs. In this paper a simple method of using this plate camera for recording a contact micrograph of thin paper on photographic cut sheet, using accelerated electrons at 80 to 100kV in a Philips transmission electron microscope has been described and discussed. Results indicate that the scattered electrons through the sheet of paper do record the structural morphology and help in characterization of paper and its quality. In addition to paper technology, this technique may find potential applications in polymer film and solid state industries and several other areas which require characterization of thin specimens.     

Hybrid retinal image registration using phase correlation

Abstract

This paper deals with registration of retinal images, which were taken by high-resolution digital colour fundus cameras. The proposed method describes successful application of phase correlation method. It combines several basic steps — global correction of shift, rotation and scaling, detection of landmarks, their correspondences and finally image registration using second-order polynomial model. The method is tested on two sets of images. The first set contains images from the diabetic patients where many retinal pathologies can disturb the registration process. The second set contains images from healthy subjects, which were acquired by different illumination conditions. The method was evaluated using four different criteria - tree objective and one subjective. These criteria are also compared. The achieved registration accuracy of the landmarks position error is 1·13 and 0·93 pixels for respective image sets. Finally, the simple scheme for retinal pathology visualisation of registered fundus pairs is presented.     

Inversion of Functional Graded Materials Elastic Properties from Ultrasonic Lamb Wave Phase Velocity Data Using Genetic Algorithm

An inverse method based on genetic algorithm (GA) is presented to determine the elastic properties of functional graded materials (FGMs) plate from lamb wave phase velocity data. The Legendre polynomial expansion method is used as a forward solver to calculate the phase velocity dispersion curves of lamb wave in FGMs plate, which has a distribution function to express the inhomogeneity of materials’ elastic properties. The properties of FGMs plate can be characterized by minimizing the standard deviations between the actual and calculated phase velocities of lamb waves. By using GA, the elastic parameters of FGMs plates with three different distribution functions are inversed, and the convergence and deviations of the inversion are also discussed. The investigation shows that this inverse method is efficient and accurate for determining the materials parameters of FGMs and the deviation can be controlled below 5 %.     

Quantization index modulation-based image watermarking using digital holography

We propose a blind watermarking method where the watermark is a hologram itself. In the proposed approach, the quantized phase of the hologram is embedded into the wavelet-transformed host image using quantization index modulation. In the detection stage, wavelet transform of the watermarked image followed by a minimum distance decoder is used. The proposed method is blind since it requires only information about the quantizers and the parameters of the hologram recording process. The robustness of the proposed technique is tested against several attacks such as filtering, compression, occlusion, and cropping. Moreover, we discuss the effect of quantization of the hologram on the reconstruction quality.     

Nonlinear techniques in optical synthetic aperture radar image generation and target recognition

One of the most successful optical signal-processing applications to date has been the use of optical processors to convert synthetic aperture radar (SAR) data into images of the radar reflectivity of the ground. We have demonstrated real-time input to a high-space-bandwidth optical SAR imagegeneration system by using a dynamic organic holographic recording medium and SAR phase-history data. Real-time speckle reduction in optically processed SAR imagery has been accomplished by the use of multilook averaging to achieve nonlinear modulus-squared accumulation of subaperture images. We designed and assembled an all-optical system that accomplished real-time target recognition in SAR imagery. This system employed a simple square-law nonlinearity in the form of an optically addressed spatial light modulator at the SAR image plane to remove the effects of speckle phase profiles returned from complex SAR targets. The detection stage enabled the creation of an optical SAR automatic target recognition system as a nonlinear cascade of an optical SAR image generator and an optical correlator.     

Pixel expansion-free grey-scale image sharing method

Abstract

In recent years, many visual secret sharing technologies have been proposed to protect the security of secret images (black and white, grey scale or colour images). In 2005, Lukac and Plataniotis used the concept of the Naor–Shamir method to propose a visual secret sharing technology for sharing secret grey-scale images based on bit-plane decomposition. Although their method can avoid pixel-value cutting problem, it still suffers from the pixel expansion problem. In this paper, we propose a new secret grey-scale image sharing method to improve this situation. In the proposed sharing image creation phase, two sharing images (one is grey-scale and the other is binary) are created and later shared by two protectors. The original secret image can be easily reconstructed if both sharing images are obtained. However, one cannot obtain the original secret image from each of the sharing images. Experimental results also show that the proposed method can effectively solve the pixel expansion problem.     

Delamination detection in composites through guided wave field image processing

This study explores the feasibility of using a non-contact guided wave imaging system to detect hidden delamination in multi-layer composites. The study is conducted in two phases. In the first phase, Lamb waves are excited by a lead (Pb) Zirconate Titanate transducer (PZT) mounted on the surface of a composite plate, and the out-of-plane velocity field is measured using a one-dimensional (1D) scanning laser Doppler vibrometer (LDV). From the scanned time signals, wavefield images are constructed and processed to study the interaction of Lamb waves with delamination. The paper presents additional signal and image processing techniques used to highlight the defect in the scanned area. The techniques are demonstrated using experimental data collected from a 1.8 mm thick multi-layer composite. In the second phase, a completely non-contact system is described to excite and measure guided waves. A modulated continuous wave (CW) laser source in conjunction with a photodiode is used to wirelessly excite an attached PZT and the resulting waves are again sensed using the vibrometer. The non-contact system is used to excite and measure elastic waves in a composite channel test article. The elastic wave propagation image sequences are created from the non-contact excitation system.     

Digital image encryption and watermarking by phase-shifting interferometry

A method for both image encryption and watermarking by three-step phase-shifting interferometry is proposed. The image to be hidden is stored in three interferograms and then can be reconstructed by use of one random phase mask, several specific geometric parameters, and a certain algorithm. To further increase the security of the hidden image and confuse unauthorized receivers, images with the same or different content can be added to the interferograms, and these images will have no or only a small effect on the retrieval of the hidden image, owing to the specific property of this algorithm. All these features and the utility of this method for image retrieval from parts of interferograms are verified by computer simulations. This technique uses intensity maps as decrypted images for delivery, and both encryption and decryption can be conveniently achieved digitally. It is particularly suitable for the remote transmission of secret information via the Internet.