三维物体空间再现技术中的全息图计算

全息空间再现技术可以记录三维(3D)物体并在空间重构出三维像，是真实地再现三维场景的一种新的可行方法。三维物体全息图的计算是全息空间再现技术中的关键技术之一。本文在简要论述三维物体计算全息技术的理论基础上，对具有代表性的三维物体全息计算方法的原理和技术要点进行了重点论述。采用了层析法、菲涅耳波带法、多视角投影合成全息法等三种方法进行了三维物体全息图的计算，并利用LCR-2500空间光调制器及650 nm的150 mW半导体激光器对层析法计算的三维物体全息图进行了光电再现，对其它两种方法获得的三维物体全息图进行了数值再现，并三种计算方法各自的特点和局限性进行了具体的分析。在对目前三维物体计算全息技术中存在的硬件和算法等关键问题进行分析的基础上，讨论了提高三维物体计算全息图的效率和质量的有效途径。     

三维物体全视差全息体视图的快速计算

针对传统全息技术对三维数据源要求高、计算量大以及实现速度慢等问题,提出了一种三维物体全视差全息体视图的快速计算方法。该方法对全息面和再现面分别进行空间分割和频谱采样,通过迭代傅里叶变换算法计算多个基元全息图,叠加构成全息图单元。由摄像机获取三维物体不同角度的二维视差图像,基于人眼双目视差立体视觉原理,构建视差图像与全息图单元的对应关系。最后,利用全视差图像调制全息图单元中对应衍射方向的基元全息图,快速合成三维物体全视差全息体视图。基于液晶空间光调制器构建的光学系统对全息体视图进行了再现实验。结果表明,与传统全息图计算方法相比,本文方法容易获取数据源,计算量较小,能够快速计算全息体视图,实现三维物体不同视角图像的再现。     

彩色全息光电再现倍率色差的消除

针对基于空间光调制器的彩色全息光电再现系统在利用计算全息图进行光电再现时会由于三色激光波长不同造成再现像出现倍率色差,影响再现效果的问题,本文重点分析了倍率色差产生的原因.为了消除倍率色差,提高彩色光电再现像的质量,提出了在全息图计算过程中对物信息进行差别采样来消除倍率色差.基于时分复用方法搭建了彩色全息光电再现系统,...     

减少液晶显示全息图的再现误差

提出计算机生成全息图的新的算法.全息条纹数据以计算机图像格式存储,并以视频信号传输到液晶板上显示,用该电全息实时三维成像.液晶板的分辨率、对比度及由全息图的灰度决定的调制度会对再现造成影响.因此在算法中考虑这些因素,并通过确定像面分布的情况下逆推求出全息面上的光波的振幅和位相分布再优化编码来减少再现误差.最后给出了实验结果,并对再现进行像质评价.     

真彩色全息图的研究

真彩色全息图的制作方法较多,为了提高真彩色全息图的质量,用安装有三色光栅的照相机直接拍摄彩色景物.通过一次暴光,把彩色景物的红、绿、蓝信息编码记录在一张与三色光栅密接的黑白胶片上,用单色激光同时再现出所记录的三种颜色的光强分布并将它们记录在一张全息片上作成彩色全息图,该方法的显著优点是制作过程中无须获得三张分色掩膜信息的全息图,改进了分色过程中的定位对准问题,提高了全息图的衍射效率,再现象的色彩明亮、保真度较高、还原性好.     

基于全息图放大的数字全息显微结构测量

针对典型预放大数字显微全息光路中存在的二次位相误差，本文设计了基于全息图放大的数字全息显微光路。此设计中，光束首先照射透明显微物体，然后与平行参考光干涉，形成全息图，最后经显微镜获得放大的全息图。这种光路从系统上直接消除了主要由球面波引起的位相畸变，有利于数字处理及实时化。作者以位相光栅(30 lines/mm，槽深约0.3 µm)作为实验样本，对此光路进行了分析研究，并分别用菲涅耳近似法和卷积法再现单幅全息图，同时获取了物体的强度信息和三维位相信息，位相深度的计算结果为0.27 µm。结果表明本文设计的光路对二次位相产生的离焦误差有明显的抑制作用。     

用四个干涉图法测压力鼓变形滞后线

本文从原理与实验论述了如何应用自动计算全息图的四个干涉图法高精度、非接触、实时地测试被物体变形的全信息：变形的大小、方向和形状。并用光导热塑料相机和计算机控制的全息装置成功地测定了压力鼓受气压后变形的滞后线。它表明，这种新的自动计算全息图的全息干涉术使全息干涉从实验室走向工业测试成为可能。     

动态物体真彩色全息图的研究

利用集成照相彩虹全息相结合的技术我们进行了动态物体真彩色全息图的研究,本文较为详细地介绍在记录介质为全色和非全色两种情况下动态物体彩色全息图的记录技术。     

电子束计算全息图的制作

本文论述了利用电子束曝光机制作计算全息图的方法及其优点。并得到了制作Lohmann型计算全息图和计算全息微分滤波器的初步实验结果。     

数字全息三维显示关键技术与系统综述

三维全息显示能够表现出与真实物体一样的深度和视差,是一种理想的三维显示方法.但是,三维物体计算全息图计算复杂且计算量巨大,因此,如何快速生成三维物体计算全息图是数字三维全息动态显示中的关键问题之一.本文首先论述了数字全息三维显示的关键技术,包括物点散射法、体视全息法、层析法等三种三维物体计算全息图实现方法,一种RGB分离的真彩色全息显示实现方法和若干提高全息再现像质的方法;然后对几种最新典型的数字三维全息显示系统进行了技术分析;最后总结了数字全息三维显示领域的发展动态,指出三维全息显示技术会朝着实时、动态、更大尺寸、更高分辨率方向发展.     

Holographic Vector Wave Femtosecond Laser Processing

Parallel femtosecond laser processing using a computer-generated hologram (CGH) displayed on a spatial light modulator (SLM), called holographic femtosecond laser processing, provides the advantages of high throughput and high energy-use efficiency. Use of a light wave with spatially controlled polarization fields, called a vector wave, also offers novel properties in various applications. In this study, we demonstrated holographic femtosecond laser processing with a vector wave by using a pair of SLMs. In particular, we performed three-dimensional reconstruction with multifocal radial beams. We also realized simultaneous reconstruction with two different types of vector beams by using a novel design method of a CGH composed of multiple small CGHs. To our knowledge, this is the first demonstration of its kind. The polarization fields of the multifocal vector beams at the sample plane were analyzed from the orientations of periodic nanostructures fabricated with femtosecond laser light.     

利用曲面计算全息图进行非球面检测

研究了利用曲面计算全息图进行非球面检测.分析了曲面计算全息图的衍射特性,给出了曲面计算全息图与传统检测方法相结合检测凹非球面和凸非球面的原理及特点,并进行了具体设计.利用激光直接写入设备,在口径为110mm、曲率半径为504mm的曲面基底上制作出了计算全息图,并对金刚石车床车削的凸面非球面进行了检测.利用两步测量法解决了凸非球面的中心部位难以检测的难题,同时利用旋转相减法消除了调节误差,非球面的面形精度为234nm(P-V),与金刚石车床的精度相符.     

用于柱面镜面形检测的CGH的设计与误差分析

现代X射线掠入射成像式望远镜是由大量的圆柱面超薄玻璃镜面经压制成圆锥面组成的准Wolter-I型望远镜。为了完成超薄玻璃圆柱面的检测,设计了适用于干涉检测的计算全息图(CGH)。结合CGH的设计制作过程,分析了CGH的基底面形误差、刻蚀占空比误差、刻蚀位置误差、刻蚀深度等误差,并对占空比、刻蚀深度的参数做了具体的分析,通过对制作误差的分析选择了制作参数。采用设计制作的CGH和ZYGO干涉仪实现了X射线望远镜用柱面镜的检测,检测结果达到了柱面镜的使用要求。     

Reconstruction of random heterogeneous media

Stochastic reconstruction is a technique to generate samples of random structures with prescribed distributional properties in the sense that certain of their statistical summary characteristics match target values or forms. This technique can be used to produce structures of any wanted size for further statistical analysis starting from small samples, which may be even only lower dimensional, for instance, when three‐dimensional imaging techniques are not available. In this review we explain the main ideas of stochastic reconstruction, concentrating on the most important case of digitized binary media and with a particular emphasis on stereological reconstruction.     

基于形态学算法分割铁谱图像研究

在铁谱图像分析与研究中,为实现对铁谱图像的准确性与自动快速分割,首先将二值化图像进行边缘干扰去除并用形态学重构滤除明暗区域,然后采用形态学膨胀与腐蚀消除目标区域内细小孔洞,最后基于形态学分水岭方法实现自动探测目标区域并分割粘连重叠磨粒,大大提高了铁谱图像分割精度,另外由于使用形态学方法处理图像,加快了图像处理的速度,使...     

Three-Dimensional Reconstruction of Welding Pool Surface by Binocular Vision

Current research of binocular vision systems mainly need to resolve the camera's intrinsic parameters before the reconstruction of three-dimensional(3D)objects.The classical Zhang'calibration is hardly to calculate all errors caused by perspective distortion and lens distortion.Also,the image-matching algorithm of the binocular vision system still needs to be improved to accelerate the reconstruction speed of welding pool surfaces.In this paper,a preset coordinate system was utilized for camera calibration instead of Zhang'calibration.The binocular vision system was modified to capture images of welding pool surfaces by suppressing the strong arc interference during gas metal arc welding.Combining and improving the algorithms of speeded up robust features,binary robust invariant scalable keypoints,and KAZE,the feature information of points(i.e.,RGB values,pixel coordinates)was extracted as the feature vector of the welding pool surface.Based on the characteristics of the welding images,a mismatch-elimination algorithm was developed to increase the accuracy of image-matching algorithms.The world coordinates of match-ing feature points were calculated to reconstruct the 3D shape of the welding pool surface.The effectiveness and accuracy of the reconstruction of welding pool surfaces were verified by experimental results.This research proposes the development of binocular vision algorithms that can reconstruct the surface of welding pools accurately to realize intelligent welding control systems in the future.     

Phase resolving microscopy by multi-plane diffraction detection

An easily applicable quantitative phase-contrast microscopy is presented. A bright-field microscope with a coherent illumination is used. Only a series of diffraction images is taken in different distances from the sample. For reconstruction, a conjugate gradient technique as a new variant of phase retrieval technique is developed. The technique is experimentally investigated in detail. A phase accuracy up to 0.07 rad or a height accuracy of 13 nm in transmission for a binary test sample is reached, respectively.     

基于压缩感知归一化关联成像实现目标重构

在归一化关联成像的基础上,结合压缩感知理论,提出了基于压缩感知的归一化关联成像方法。该方法首先对物臂的桶探测值进行归一化处理,并由散斑场构造测量矩阵;然后采用正交匹配追踪算法,在低测量次数下优质量地还原出了物体的像。实验中采用灰度图像及二值图像作为成像目标,以峰值信噪比作为衡量标准,分别对传统关联成像,归一化关联成像及压缩感知归一化关联成像的重构效果进行了量化对比。仿真实验结果表明,对于细节较为丰富的灰度图像,压缩感知归一化关联成像的峰值信噪比较传统方法高6dB左右,比归一化关联成像方法提高了2dB左右;对于细节较少的二值图像,其峰值信噪比较归一化关联成像法高3.4~4.3dB,比传统法高5.2~6.5dB。最后,采用实际电荷耦合元件测得的散斑场构造了测量矩阵,实验结果进一步验证了基于压缩感知的归一化关联成像算法能提高重构质量。     

Measurements of the characteristics of spray droplets using in-line digital particle holography

In-line digital particle holography is applied to measure the characteristics of spray droplets. Common reconstruction methods were considered and the best one was selected. Several important parameters at the time of hologram recording, such as the object distance and the region of laser beam used, are discussed. The feasibility of the correlation coefficient (CC) method for focal plane determination of 3-D droplets was verified. A double exposure hologram recording system with synchronization system for time control was established, and two digital spray holograms were obtained in a short time interval. For post-processing of reconstruction images, the two-threshold and the image segmentation methods were used in binary image transformation. Using the CC method and some image processing techniques applied to droplets in each double exposure image, the spatial positions of droplets used to evaluate the three dimensional droplet velocities were easily located, which proved the feasibility of in-line digital particle holographic technology as a good measurement tool for spray droplets. This paper was recommended for publication in revised form by Associate Editor Gihun Son Boseon Kang received his B.S. and M.S. degrees in Mechanical Engineering from Seoul National University in 1986 and 1988, respectively. He then went on to receive his Ph.D. degree from University of Illinois, Chicago in 1995. He is currently Professor at School of Mechanical Systems Engineering, Chonnam National University in Gwangju, Korea. His research interests are in the area of sprays, holographic techniques in thermofluid measurements. Yan Yang received his B.S. degree in Mechanical Engineering from Chongqing Insitute of Technology in 1997, and received his M.S. degree in Mechanics from Chongqing University in 2005. He is doctoral student of Department of Mechanical Systems Engineering, Chonnam National University in Gwangju, Korea. He is also currently Associate Professor at Automobile College, Chongqing University of Technology in Chongqing, China. His research direction is digital holographic techniques