Incoherent holographic imaging through thin turbulent media

We introduce and experimentally demonstrate a new method of computing Fresnel holograms of a real-existing, three-dimensional (3-D) scene hidden behind a thin turbulent medium, and illuminated by incoherent white light. From each perspective point of view, we acquire multiple noisy speckled images through the medium vibrated mechanically. These images are fused together to yield a smoothed perspective projection of the hidden 3-D scene. All smoothed projections are processed to yield a Fresnel hologram of the hidden scene. The 3-D image reconstructed from the hologram is further improved by digital blind deconvolution of each of the 3-D image slices with its own estimated impulse response.     

Perfect digital holographic imaging with high resolution using a submillimeter-dimension CCD sensor

In order to improve the resolution of digital holography with a common-dimension charge-coupled device (CCD) sensor, the point spread functions are briefly derived for the commonly used and practical post-magnification, pre-magnification, and image-plane digital holographic microscopic systems. The ultimate resolutions of these systems are analyzed and compared. The results show that the ultimate lateral resolution of pre-magnification digital holography is superior to that of post-magnification digital holography in the same conditions. We also demonstrate that the ultimate lateral resolution of image-plane digital holography has no correlation with the photosensitive dimension of the CCD sensor, and it is not significantly related to the pixel size of the sensor. Moreover, both the ultimate resolution and the imaging quality of image-plane digital holography are superior to that of pre- and post-magnification digital holographic microscopy. High-resolution imaging, whose resolution is close to the ultimate resolution of the microscope objective, can be achieved by image-plane digital holography even with a submillimeter-dimension sensor. This system, by which perfect imaging can be achieved, is optimal for commonly used digital holographic microscopy. Experimental results demonstrate the correctness of the theoretical analysis.     

Path-independent digital image correlation with high accuracy,speed and robustness

The initial guess transferring mechanism is widely used in iterative DIC algorithms and leads to path-dependence. Using the known deformation at a processed point to estimate the initial guess at its neighboring points could save considerable computation time, and a cogitatively-selected processing path contributes to the improved robustness. In this work, our experimental study demonstrates that a path-independent DIC method is capable to achieve high accuracy, efficiency and robustness in full-field measurement of deformation, by combining an inverse compositional Gauss–Newton (IC-GN) algorithm for sub-pixel registration with a fast Fourier transform-based cross correlation (FFT-CC) algorithm to estimate the initial guess. In the proposed DIC method, the determination of initial guess accelerated by well developed software library can be a negligible burden of computation. The path-independence also endows the DIC method with the ability to handle the images containing large discontinuity of deformation without manual intervention. Furthermore, the possible performance of the proposed path-independent DIC method on parallel computing device is estimated, which shows the feasibility of the development of real-time DIC with high-accuracy.     

A holographic image printing technique with high resolution

A method is shown to obtain a real image with a large image field and high resolution from an image hologram, which is produced by a large aperture lens with large amount of aberration. The resolution of the reconstructed serial image is estimated to be within the range from 450 to 500 lines/mm in 2 inch diameter image field.     

数字全息重建图像的焦深研究

将来自物体的散射光视为物体表面相位随机取值的大量点源发出光波的叠加, 对数字全息重建像及离焦像的衍射场进行研究. 基于重建像以像素为单位显示的特点, 对焦深作出新的定义, 然后, 根据重建像的像素物理尺寸与计算方法相关的特点, 推导出不同重建算法重建图像的焦深表达式, 最后给出相关的实验证明.     

高温下数字图像相关散斑最优成像探究

为了测量材料在高温甚至超高温下的力学性能,采用数字图像相关方法,并研究其在高温下的最优成像。采取不同的散斑制作方法,同时加入不同颜色的高温漆,在不同的温度节点,外加不同光源及相应的滤波片,采集并观察图像是否具有良好的对比度。普通的单色光源在800℃以后会逐渐失效,无法获取图像,而紫外光在1 200℃时依然可以获取较好的图像,且直接利用试件本身颜色作为底色效果更佳。采用紫外光照明可以实现DIC在高温环境下的测量。同时利用黑色或者蓝色散斑直接喷涂在试件上有着最佳的对比度,要优于常规的散斑制作方法。     

4-D imaging of fluid flow with digital in-line holographic microscopy

The large depth of field of digital in-line holographic microscopy (DIHM) with numerical reconstruction provides an ideal tool for the study of microfluidic phenomena. As indicators of the flow patterns we use latex microspheres and also red blood cells whose three-dimensional trajectories and velocities can easily be measured as a function of time with subsecond and micron resolution. We demonstrate the efficiency of DIHM by showing 3-D views of the flow patterns around big spheres in various geometric arrangements.     

Extended focused imaging of a microparticle field with digital holographic microscopy

We present a numerical technique for extended focused imaging and three-dimensional analysis of a microparticle field observed in a digital holographic microscope working in transmission. The three-dimensional localization of objects is performed using the local focus plane determination method based on the integrated amplitude modulus. We apply the refocusing criterion locally for each pixel, using small overlapping windows, to obtain the depth map and a synthetic image in which all objects are refocused independent from their refocusing distance. A successful application of this technique in the analysis of the microgravity particle flow experiment is presented.     

菲涅耳数字全息成像系统的脉冲响应分析

数字全息成像由CCD记录数字全息图后经过计算机数值重建物光波场,这个过程从傅里叶变换角度看等同于数字全息图的频谱分析。讨论了数字成像系统的脉冲响应函数,并分别推导了其实像、虚像、零级像在平面波和球面波照射下的波前复振幅分布。结果表明,实像和虚像是移位的夫琅和费衍射分布,而零级像是CCD光瞳的菲涅耳衍射分布,且与参考光波前分布无关。     

球面参考光预放大数字全息成像系统分辨力

为了提高数字全息成像系统的成像分辨力,对以球面波作为参考光波的预放大数字全息成像系统的记录和再现过程进行了理论推导,得出了该系统的脉冲响应表达式,并由此分析了决定该系统成像分辨力的因素。在CCD成像分辨力高于显微物镜分辨力的情况下,通过对分辨力测试板进行实验,讨论了系统分辨力与记录距离的关系。结果表明：再现像的分辨力对记录距离不敏感;但在记录距离为零,即像面数字全息系统下,再现像具有更高的分辨力。实验结果与理论分析一致。     

球面参考光预放大数字全息成像系统分辨力

为了提高数字全息成像系统的成像分辨力,对以球面波作为参考光波的预放大数字全息成像系统的记录和再现过程进行了理论推导,得出了该系统的脉冲响应表达式,并由此分析了决定该系统成像分辨力的因素。在CCD成像分辨力高于显微物镜分辨力的情况下,通过对分辨力测试板进行实验,讨论了系统分辨力与记录距离的关系。结果表明:再现像的分辨力对记录距离不敏感;但在记录距离为零,即像面数字全息系统下,再现像具有更高的分辨力。实验结果与理论分析一致。     

Delayed range-gating super-resolution imaging lidar with high accuracy

We present a range-gating delayed detection super-resolution imaging lidar with high accuracy based on the signal intensities of three consecutive delay samples. The system combines the range and signal intensity information from multi-pulse detections to calculate the pulse peak position under the assumption of a Gaussian pulse shape. Experimental results indicate that the proposed algorithm effectively calculates pulse peak position and exhibits excellent accuracy with super-resolution. Accuracy analysis shows that accuracy is best improved by enhancing signal-to-noise ratio, strategically selecting samples, reducing pulse width, and appropriately choosing the delayed periods between samples.     

实时全息干涉视频图像自动化处理及应用研究

研究了实时全息干涉条纹视频图像计算机自动处理技术。采用Delphi可视化软件为开发工具,在Win dows环境下播放实时全息干涉图像,并同时获取在播放窗口中任意指定的灰度值、自动描绘灰度 时间以及位移 时间曲线。对测试原理和图像去噪、曲线平滑等关键处理技术进行了介绍。通过对微电子产品热变形研究的实例分析,显示了该自动处理软件的操作便捷、实用和先进性。     

数字全息显微像平面相位畸变的自动补偿研究

对离轴数字全息显微相位畸变的自动补偿进行了理论和实验研究。首先对由CCD记录的数字全息图采用平均梯度自聚焦方法确定最佳再现距离,然后将修正的虚拟参考光作用于切趾滤波后的全息图进行数字再现,经像平面相位自动补偿后得到无畸变的物体相位分布。该方法仅需记录一幅离轴数字全息图就可以自动快速地重建物体的真实相位信息。     

An approach for sensing marine plankton using digital holographic imaging

The goal of this paper is to use digital holographic imaging for sensing marine plankton in recording sampling volume. The process stage of this approach includes: wavefront recording using in-line holographic recording set up and numerical reconstruction using Fresnel approximation and convolution algorithm. So, by capturing hologram of marine plankton and reconstructing hologram, the recorded optical field of marine plankton is retrieved. Digital holographic imaging is an extremely powerful technique for the study of marine plankton fields as it allows instantaneous, noninvasive, high-resolution recording of substantial volumes. Finally, this paper presents that it is possible for digital holographic imaging system to sense marine plankton according to laboratory results.     

多探测器拼接成像系统实时图像配准

依据已设计完成的基于同心球透镜的四镜头多探测器阵列拼接成像系统,对该系统图像拼接配准过程所采用的特征检测提取、特征向量匹配与筛选、空间变换模型参数估计等算法进行了研究。首先,采用Fast-Hessian检测子提取参考图像和待配准图像的特征点,并生成加速鲁棒特征(SURF)描述向量。接着,采用快速近似最近邻(FANN)逼近搜索算法获得初始的匹配点对,并对匹配点对特征向量的欧式距离进行排序。然后,参照成像系统光学设计参数设定合理的阈值,筛选并保留下较好的匹配点对。最后,提出了一种改进的渐进式抽样一致性(IPROSAC)算法对空间变换矩阵模型进行参数估计,从而得到参考图像与待配准图像的空间几何变换关系。实验结果表明:该算法对图像尺寸、旋转和光照变化都具有一定的不变性,特征匹配时间为0.542 s,配准变换时间0.031 s,配准误差精度小于0.1 pixel,可以满足成像系统关于图像配准实时性和准确性的要求,具有一定的工程应用价值。     

Long-term quantitative phase-contrast imaging of living cells by digital holographic microscopy

The dynamic analysis of biological living samples is one of the particular interests in life sciences. An improved digital holographic microscope for long-term quantitative phase-contrast imaging of living cells is presented in this paper. The optical configuration is optimized in the form of a free-space-fiber hybrid system which promotes the flexibility of imaging in complex or semi-enclosed experimental environment. Aberrations compensation is implemented taking into account the additional phase aberration induced by liquid culture medium in long-term observation. The proposed approach is applied to investigate living samples of MC3T3-E1 and MLO-Y4 cells. The experimental results demonstrate its availability in the analysis of cellular changes.     

Label-free second-harmonic phase imaging of biological specimen by digital holographic microscopy

We have previously developed a new way for nonscanning second-harmonic generation (SHG) microscopy [Opt. Lett. 34, 2450 (2009)]. Based on digital holography, this technique captures, in single-shot hologram acquisition, both the amplitude and the phase of a coherent SHG radiation, which makes possible second harmonic phase microscopy. In this work, we present holographic SHG phase microscopy of a label-free biological tissue and discuss its added value to SHG microscopy.     

Phase correction and resolution improvement of digital holographic image in numerical reconstruction with angular multiplexing

A phase correction method is presented to remove the phase slope of the sub-holograms caused by the multi-direction illumination on object in digital holography. To improve the resolution of the reconstructed holographic images, two sub-holograms are recorded by using angular multiplexing and their phase slope parameter is obtained by theoretical analysis. Introducing a phase correction parameter to this phase slope, the ideal complex reconstructed image can be obtained by superposing the reconstructed object wave fields of the two sub-holograms. Experimental results demonstrate that the resolution of the reconstructed image can be effectively enhanced.     

全息滤波光学图像相减

基于傅里叶光学二次滤波技术,本文提出了一种新的光学图像相减方法,即全息滤波光学图像相减法,该方法需用图像的逆转和匹配两种滤波器和一个8f光学系统,实验表明,作为一种新的图像相减方法,避免了以往实时法对光程的精细控制,因而降低了对辅助设备和环境的要求.