Three-dimensional matching by use of phase-only holographic information and the Wigner distribution

Matching of three-dimensional (3-D) objects is achieved by Wigner analysis of the correlation pattern between the phase-only holographic information of a reference object and that of a target object. First, holographic information on the reference object and on the target object is extracted by use of optical scanning holography as a form of electrical signal. This electrical information is then stored in a computer for digital processing. In the digital computer, the correlation between the phase-only information of the hologram of the reference object and that of the target object is calculated and analyzed by use of a Wigner distribution. The Wigner distribution yields a space-frequency map of the correlation pattern that indicates whether the 3-D image of the target object matches that of the reference object. When the 3-D image of the target object matches that of the reference object, the Wigner distribution gives a well-defined line that directly indicates the 3-D location of the matched target object. Optical experiments with digital processing are described to demonstrate the proposed matching technique.     

Fast acquisition system for digital holograms and image processing for three-dimensional display with data manipulation

A three-dimensional (3D) digital holographic display system with image processing is presented. By use of phase-shifting digital holography, we obtain the complex amplitude of a 3D object at a recording plane. Image processing techniques are introduced to improve the quality of the reconstructed 3D object or manipulate 3D objects for elimination and addition of information by modifying the complex amplitude. The results show that the information processing is effective in such manipulations of 3D objects. We also show a fast recording system of 3D objects based on phase-shifting digital holography for display with image processing. The acquisition of 3D object information at 500 Hz is demonstrated experimentally.     

彩色全息的进展

本文介绍真彩色全息技术的进展，包括早期的彩色全息术，白光处理彩色全息术，透射彩色彩虹全息术，彩色傅里叶变换全息术，反射彩色全息术。阐述全息图的构成与再现过程，给出了这些技术的实验例证。     

声全息技术的研究现状与展望

简单地回顾了全息术的基本原理,全息术的应用范围及发展历史。对声全息技术进行了分类，并对各类声全息技术的特点进行了评述，就近场声全息技术（NAH）中常用的各类重建计算方法及适用范围、声全息数据的各类采集方法、特点及声全息成像的分辨率、各类声场全息图像的表达方法等问题的研究现状进行了详尽的分析，并重点分析了基于声压测量的近场声全息技术和基于声强测量的近场声全息技术（BAHIM）的研究现状，从而指出了这两种近场声全息技术有待进一步深入研究的问题，并对NAH及BAHIM技术发展前景进行了展望。     

Coal powder measurement by digital holography with expanded measurement area

The field of view of digital in-line holography for flow field diagnostics is restricted to a small volume due to the finite size and the low spatial resolution of the available CCD. Expansion of the measurement cross section of digital holographic particle image velocimetry was investigated with a lens-based holography configuration. By sampling the chirp signal in the center lobe completely and undersampling the chirp signal in the second- and higher-order lobes by a magnified virtual recording plane produced by an imaging camera lens, the field of view is expanded. Simulation results show that the three-dimensional (3D) location and size of the relatively large particle can be reconstructed with good accuracy. A digital holographic particle image velocimetry system was established for coal particle flow field diagnostics. Compared with the lensless configuration, the field of view of the digital holography system was enlarged 1.9 times, up to 2.78 cm × 2.78 cm × 3 cm. The 3D location, size distribution, and the 3D vector field of coal powder were obtained. The results show that the application of digital in-line holography to measure large particle flow field is feasible.     

Magnified reconstruction of digitally recorded holograms by Fresnel-Bluestein transform

A method for numerical reconstruction of digitally recorded holograms with variable magnification is presented. The proposed strategy allows for smaller, equal, or larger magnification than that achieved with Fresnel transform by introducing the Bluestein substitution into the Fresnel kernel. The magnification is obtained independent of distance, wavelength, and number of pixels, which enables the method to be applied in color digital holography and metrological applications. The approach is supported by experimental and simulation results in digital holography of objects of comparable dimensions with the recording device and in the reconstruction of holograms from digital in-line holographic microscopy.     

Space-bandwidth conditions for efficient phase-shifting digital holographic microscopy

Microscopy by holographic means is attractive because it permits true three-dimensional (3D) visualization and 3D display of the objects. We investigate the necessary condition on the object size and spatial bandwidth for complete 3D microscopic imaging with phase-shifting digital holography with various common arrangements. The cases for which a Fresnel holographic arrangement is sufficient and those for which object magnification is necessary are defined. Limitations set by digital sensors are analyzed in the Wigner domain. The trade-offs between the various holographic arrangements in terms of conditions on the object size and bandwidth, recording conditions required for complete representation, and complexity are discussed.     

Digital holography of particle fields: reconstruction by use of complex amplitude

Digital holography appears to be a strong contender as the next-generation technology for holographic diagnostics of particle fields and holographic particle image velocimetry for flow field measurement. With the digital holographic approach, holograms are directly recorded by a digital camera and reconstructed numerically. This not only eliminates wet chemical processing and mechanical scanning, but also enables the use of complex amplitude information inaccessible by optical reconstruction, thereby allowing flexible reconstruction algorithms to achieve optimization of specific information. However, owing to the inherently low pixel resolution of solid-state imaging sensors, digital holography gives poor depth resolution for images, a problem that severely impairs the usefulness of digital holography especially in densely populated particle fields. This paper describes a technique that significantly improves particle axial-location accuracy by exploring the reconstructed complex amplitude information, compared with other numerical reconstruction schemes that merely mimic traditional optical reconstruction. This novel method allows accurate extraction of particle locations from forward-scattering particle holograms even at high particle loadings.     

Intrinsic speckle noise in off-axis particle holography

In holographic imaging of particle fields, the interference among coherent wave fronts associated with particle scattering gives rise to intrinsic speckle noise, which sets a fundamental limit on the amount of information that particle holography can deliver. It has been established that the intrinsic speckle noise is especially severe in in-line holography because of superposition of virtual image waves, the direct transmitted wave, and the real image. However, at sufficiently high particle number densities, such as those typical in holographic particle image velocimetry (HPIV) applications, intrinsic speckle noise also arises in off-axis particle holography from self-interference among wave fronts that form the real image of particles. To overcome the latter problem we have constructed a mathematical model that relates the first- and second-order statistical properties of the intrinsic speckle noise to relevant holographic system parameters. Consistent with our experimental data, the model provides a direct estimate of the information capacity of particle holography. We show that the noise-limited information capacity can be expressed as the product of particle number density and the extent of the particle field along the optical axis. A large angular aperture of the hologram contributes directly to achievement of high information capacity. We also show that filtering in either digital or optical form is generally ineffective in removing the intrinsic speckle noise from the particle image as a result of the similar spectral properties of the two. These findings emphasize the importance of angular aperture in designing holographic particle imaging systems.     

Penalized-likelihood image reconstruction for digital holography

Conventional numerical reconstruction for digital holography using a filter applied in the spatial-frequency domain to extract the primary image may yield suboptimal image quality because of the loss in high-frequency components and interference from other undesirable terms of a hologram. We propose a new numerical reconstruction approach using a statistical technique. This approach reconstructs the complex field of the object from the real-valued hologram intensity data. Because holographic image reconstruction is an ill-posed problem, our statistical technique is based on penalized-likelihood estimation. We develop a Poisson statistical model for this problem and derive an optimization transfer algorithm that monotonically decreases the cost function at each iteration. Simulation results show that our statistical technique has the potential to improve image quality in digital holography relative to conventional reconstruction techniques.     

Digital holographic microscope for measuring three-dimensional particle distributions and motions

Better understanding of particle-particle and particle-fluid interactions requires accurate 3D measurements of particle distributions and motions. We introduce the application of in-line digital holographic microscopy as a viable tool for measuring distributions of dense micrometer (3.2 microm) and submicrometer (0.75 microm) particles in a liquid solution with large depths of 1-10 mm. By recording a magnified hologram, we obtain a depth of field of approximately 1000 times the object diameter and a reduced depth of focus of approximately 10 particle diameters, both representing substantial improvements compared to a conventional microscope and in-line holography. Quantitative information on depth of field, depth of focus, and axial resolution is provided. We demonstrate that digital holographic microscopy can resolve the locations of several thousand particles and can measure their motions and trajectories using cinematographic holography. A sample trajectory and detailed morphological information of a free-swimming copepod nauplius are presented.     

Comparative study of various endoscopes for pulsed digital holographic interferometry

A comparison of several endoscopes as object image carriers in pulsed digital holography is presented. Three multicore flexible fiber endoscopes of different spatial resolution and one rigid endoscope are investigated. The four endoscopes are integrated in a setup for the recording of digital holograms on a CCD camera. A double-pulsed ruby laser is used as the light source. A spatial carrier is introduced by an off-axis reference beam, which permits quantitative evaluation of the phase difference between two holograms recorded with a short time separation (5-600 micros). From reported studies it may be inferred that the quality of the phase maps so derived from digital holographic interferometry has a strong correlation to the spatial resolution of the multicore fiber used in these endoscopes. With the endoscopic technique combined with pulsed digital holography a number of useful applications (in areas such as medical endoscopy, micromechanics, and microelectronics) are envisaged for which access to the objects of interest is otherwise difficult.     

基于EALCD的数字全息的研究

采用一种新的数字全息再现方法,将电荷耦合器件CCD与电寻址液晶EALCD相结合实现数字全息的再现.同时将数字图像处理技术与数字全息术相结合,应用MATLAB软件对记录的全息图进行数字图像处理,实验结果表明,该方法简单快速.通过图像增强等方法对全息图进行数字图像处理,在全息再现中,全息干涉图的对比度得到了显著的提高,有利于全息干涉条纹的自动判读.     

基于归一化的全息水印技术

提出了一种结合了归一化技术和全息技术的数字水印技术。首先,利用归一化技术对图像作归一化运算,同时利用全息技术将水印二值图处理为全息图;其次,取归一化后图像分块离散余弦变换的中频系数,对中频系数所组成的矩阵作离散小波变换;最后将全息图嵌入到离散小波变换的低频分量中。由于图像归一化技术具有抗仿射变换的性能,同时全息技术具有很强的抗裁切的性能,所以此数字水印技术具有很强的抗仿射变换的性能,可以广泛的用于数字作品的版权保护。     

Optical wavelet transforms from computer-generated holography

An optical implementation of a wavelet transform is presented. Optical Haar wavelets are created by the use of computer-generated holography. Two different holographic techniques are explored: (1) interferogram and (2) detour-phase. A discrete representation of a continuous wavelet transform is obtained by the optical correlation of an image with a Haar mother wavelet. Experimental results are compared with their digital simulations.     

Holography in phase space

Holography is reformulated by using the framework of phase-space optics. The Leith-Upatnieks off-axis reference hologram is compared with precursors, namely, single-sideband holography. The phase-space representation of complex amplitudes focuses on similarities between different holographic recording schemes and is particularly useful for investigating the degree of freedom and the space-bandwidth product of optical signals and systems. This allows one to include computer-generated holography and recent developments in digital holography in the discussion.     

Underwater digital holography for studies of marine plankton

Conventional and digital holographies are proving to be increasingly important for studies of marine zooplankton and other underwater biological applications. This paper reports on the use of a subsea digital holographic camera (eHoloCam) for the analysis and identification of marine organisms and other subsea particles. Unlike recording on a photographic film, a digital hologram (e-hologram) is recorded on an electronic sensor and reconstructed numerically in a computer by simulating the propagation of the optical field in space. By comparison with other imaging techniques, an e-hologram has several advantages such as three-dimensional spatial reconstruction, non-intrusive and non-destructive interrogation of the recording sampling volume and the ability to record holographic videos. The basis of much work in optics lies in Maxwell's electromagnetic theory and holography is no exception: we report here on two of the numerical reconstruction algorithms we have used to reconstruct holograms obtained using eHoloCam and how their starting point lies in Maxwell's equations. Derivation of the angular spectrum algorithm for plane waves is provided as an exact method for the in-line numerical reconstruction of digital holograms. The Fresnel numerical reconstruction algorithm is derived from the angular spectrum method. In-line holograms are numerically processed before and after reconstruction to remove periodic noise from captured images and to increase image contrast. The ability of the Fresnel integration reconstruction algorithm to extend the reconstructed volume beyond the recording sensor dimensions is also shown with a 50% extension of the reconstruction area. Finally, we present some images obtained from recent deployments of eHoloCam in the North Sea and Faeroes Channel.     

基于计算全息的Contourlet域数字水印算法

目的提出一种基于计算全息的contourlet域数字水印算法。方法首先,利用共轭对称延拓傅里叶计算全息方法,将原始二值水印图像生成全息水印图像;然后,将原始图像进行二级contourlet变换,得到8个中频方向子带系数;最后,将全息水印嵌入在其中频系数中。结果该方法可以有效抵抗高斯滤波、中值滤波和均值滤波以及打印-扫描攻击,同时,对噪声攻击、裁切攻击和JPEG压缩攻击也有很强的抵抗能力。在水印提取时无需原始图像,属于盲水印算法。结论该算法可以广泛应用于数字图像的版权保护中。     

基于全息水印印刷防伪的半色调算法

分析了数字全息水印技术和数字图像半色调技术中的调幅半色调、调频半色调和AM/FM混合半色调3类主要技术的优势。探讨了将数字全息水印和数字图像半色调化技术紧密结合起来的数字全息水印防伪技术,并介绍了其原理、特点及应用。     

Autofocusing in digital holographic phase contrast microscopy on pure phase objects for live cell imaging

Digital holography enables a multifocus quantitative phase microscopy for the investigation of reflective surfaces and for marker-free live cell imaging. For digital holographic long-term investigations of living cells an automated (subsequent) robust and reliable numerical focus adjustment is of particular importance. Four numerical methods for the determination of the optimal focus position in the numerical reconstruction and propagation of the complex object waves of pure phase objects are characterized, compared, and adapted to the requirements of digital holographic microscopy. Results from investigations of an engineered surface and human pancreas tumor cells demonstrate the applicability of Fourier-weighting- and gradient-operator-based methods for robust and reliable automated subsequent numerical digital holographic focusing.