Gyrator变换计算全息图及其新型编码方法

基于gyrator变换数值算法和计算全息理论提出了gyrator变换计算全息图,采用罗曼编码方法制作出了在不同变换角度下的gyrator变换计算全息图并实现了相应的数字再现,其再现规律与相关文献报道的gyrator变换全息图的再现规律一致,表明制作gyrator变换计算全息图是可行的。在此基础上提出了一种新的计算全息编码方法即梯形等效面积编码方法,该方法能有效提高在单个抽样单元中进行相位编码时的相位量化级数。应用该编码方法完成了傅里叶变换计算全息图的产生和数字再现的仿真实验,实验表明采用新型编码方法的离轴物体的计算全息图能实现零级衍射成像。采用新型编码方法也实现了gyrator变换计算全息图的产生和数字再现的仿真实验。上述实验结果表明本文提出的新型编码方法是可行的和有效的。     

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.     

调频加网对于全息再现图像的影响

目的 对全息图进行加网处理,实现计算全息图的二值化,将计算全息图应用于印刷领域。方法 本文设计计算全息图进行调频加网的整体方案,讨论不同的加网算法对计算全息再现图像的质量影响。首先,对3幅不同类型的灰度图片进行计算全息编码得到全息图;然后利用误差扩散算法和抖动算法对全息图进行调频加网获得二值化全息图;之后通过光场重建得到全息再现图像。结果 对全息再现图像进行峰值信噪比和结构相似性数据比较发现,误差扩散算法更适用于计算全息二值化处理,抖动加网使计算全息图产生周期性图案,导致再现全息图产生混频现象,全息再现图像的质量下降。结论 加网导致全息图再现质量下降,误差扩散算法可以得到较好的再现像,适用于全息图的二值化处理;与此同时,抖动算法会产生混频现象,因此抖动算法并不适用于全息图二值化处理。     

压缩感知重建离轴菲涅耳全息图

针对基于传统数字全息重建算法对待测物体的不同纵向深度截面进行聚焦重构时,聚焦面物体会受到共轭像及背景离焦物体的干扰,本文提出基于压缩感知理论,构建单幅离轴菲涅耳数字全息图层析成像的算法框架。该方法通过自适应空间滤波技术对全息图进行处理,基于压缩感知理论重构不同纵向深度截面图像,并有效抑制背景离焦物体的干扰,最终达到层析成像的目标。计算机数值模拟以及三维待测物体实验结果表明该方法的有效性和可行性。     

同轴数字全息视频动态跟踪处理实验

用数字全息进行动态观测时,由于不同物体记录距离不同,且不断地变化,再现像不能始终处于清晰状态。本文提出了利用同轴数字全息视频技术实现在三维空间内对运动物体进行连续动态观测的方法,研究了其中的动态跟踪聚焦算法和视频处理算法。利用上一帧再现像中观测物体的中心位置作为下一帧全息再现中聚焦窗口的中心位置,使聚焦窗口始终跟随观测目标移动,从而保证处理全息视频时每一帧再现像都能准确自动聚焦,使再现视频中要观测的目标始终处于清晰状态。采用上一帧的聚焦距离为下一帧再现距离的搜索中心、避免处理不同全息图时的重复运算等方式来提高数字全息视频的处理速度。实验结果表明,本文提出的数字全息视频成像技术能实现在三维空间内对某一特定运动物体进行连续动态观测。     

医学层析图像的计算全息三维可视化

提出了一种医学层析图像的计算全息三维可视化技术。首先研究了层析图像序列的三维信息融合,将层析图像序列的二维信息融合成三维信息,用计算全息图的方法进行三维信息记录。然后结合空间光调制器的结构特性,对全息系统的空间频率、参物光夹角、取样间隔以及全息再现像的再现区域和视角等进行了讨论和分析,并设置了相关参数,使计算全息系统与电子显示系统相匹配。最后用液晶空间光调制器作为全息图显示载体,用计算机控制全息图的实时输出,用雾屏承载三维空间再现像,建立三维图像光电再现与实时显示系统,实现层析图像序列的三维可视化,给出了理论分析与实验结果。     

利用菲涅尔波带法计算三维全息

根据全息理论,从点光源菲涅尔全息图的计算出发,提出一种利用主菲涅尔波带计算三维物体菲涅尔全息图的方法。通过读取 3DS 文件直接获得三维物体表面各点的空间位置信息,模仿物理全息计算出点的菲涅尔图,将组成三维物体的各点的菲涅尔波带叠加从而获得三维物体的全息图。该方法区别于用菲涅尔衍射公式的传统全息计算,用加法运算代替指数、乘除运算,从而大大加快了计算输出全息图的速度,且具有信息连续、无冗余信息等特点。实验对由 1060 个采样点组成的物体进行全息计算,生成一幅 1024×768 的全息图,所需时间为 83s。     

全息信息存贮实验系统的研制

本文介绍一种激光全息信息存贮实验系统,包括光路分析、主要机械装置、电控功能、系统特点及实验结果等方面。此系统利用付里叶变换全息图的原理,将胶片上的图象信息以点阵全息图的形式存贮在全息干板上,并用电子控制装置使全息图的记录和再现过程都能自动进行。     

消除零级衍射和循环移位改善计算机合成全息图的再现质量

分析了影响计算机合成全息再现像质量的主要因素,提出了一种改善计算机合成全息再现像质量的方法。零级衍射严重降低了再现像的对比度,连续两次离散傅里叶变换的循环移位作用使得再现虚像最后一行和最后一列被分别循环移位到第一行和第一列。采用Burch型合成全息图再现算法消除了零级衍射,调整像素的位置消除了虚像的循环移位,使得全息图能够精确恢复原始图像,实验证明这种方法能改善再现像质量。     

CT图像的计算机制全息三维重建

提出用计算机制全息术实现CT图像的三维重建。首先研究了CT图像的三维信息融合,用计算机模拟CT图像的物光波,用菲涅耳计算全息图的方法,把CT图像的二维信息融合成三维信息,获得菲涅耳全息图。然后将计算机制全息与光学全息相结合,记录彩虹全息图。最后用扩展的白光再现,获得逼真无畸变的真正的三维立体图像,充分发挥了计算机制全息与光学全息的优势。在全息图的计算中利用了快速傅里叶算法,大大缩短计算时间。根据不同的观察需要制作了两种不同效果的全息图,并给出了理论分析和实验结果。     

Scheme to improve the reconstructed image in parallel quasi-phase-shifting digital holography

We propose a scheme to improve the reconstructed image in parallel quasi-phase-shifting digital holography. Parallel quasi-phase-shifting digital holography is a technique capable of noiseless instantaneous measurement of three-dimensional objects, and it implements four kinds of phase shifting at a time with an array of 2 x 2 phase-shifting devices located in the reference wave. In the phase-shifting calculation in the reconstruction process of the technique, the scheme assigns the 2 x 2 cell configuration for each pixel in the vertical direction and for each 1-pixel interval in the horizontal direction of the hologram recorded by the image sensor. We conduct both a numerical simulation and a preliminary experiment. The results show that the proposed scheme can improve the quality of the reconstructed image calculated by the conventional scheme of parallel quasi-phase-shifting digital holography we previously proposed, and then the effectiveness of the proposed scheme is verified.     

Digital holographic reconstruction of a local object field using an adjustable magnification

In the research of digital holography, this paper presents a numerical method using an adjustable magnification for local object field reconstruction together with experiment verification. The method first designs a spherical wave according to the given magnification to illuminate the digital hologram, then through a Fourier transform of diffraction, it calculates the reconstructed image plane. Afterward, a filtering window is set in the image plane to extract the image of the local object field, and then the object field reached hologram plane is formed using diffraction's inverse operation. Finally, the object field is reconstructed through diffraction's angular spectrum theory.     

Pixel-size-maintained image reconstruction of digital holograms on arbitrarily tilted planes by the angular spectrum method

We present an effective method for the pixel-size-maintained reconstruction of images on arbitrarily tilted planes in digital holography. The method is based on the plane wave expansion of the diffraction wave fields and the three-axis rotation of the wave vectors. The images on the tilted planes are reconstructed without loss of the frequency contents of the hologram and have the same pixel sizes. Our method shows good results in the extreme cases of large tilting angles and in the region closer than the paraxial case. The effectiveness of the method is demonstrated by both simulation and experiment.     

Digitized holography: modern holography for 3D imaging of virtual and real objects

Recent developments in computer algorithms, image sensors, and microfabrication technologies make it possible to digitize the whole process of classical holography. This technique, referred to as digitized holography, allows us to create fine spatial three-dimensional (3D) images composed of virtual and real objects. In the technique, the wave field of real objects is captured in a wide area and at very high resolution using the technique of synthetic aperture digital holography. The captured field is incorporated in virtual 3D scenes including two-dimensional digital images and 3D polygon mesh objects. The synthetic field is optically reconstructed using the technique of computer-generated holograms. The reconstructed 3D images present all depth cues like classical holograms but are digitally editable, archivable, and transmittable unlike classical holograms. The synthetic hologram printed by a laser lithography system has a wide viewing zone in full-parallax and give viewers a strong sensation of depth, which has never been achieved by conventional 3D systems. A real hologram as well as the details of the technique is presented to verify the proposed technique.     

Viewing-zone enlargement method for sampled hologram that uses high-order diffraction

We demonstrate a method of enlarging the viewing zone for holography that has holograms with a pixel structure. First, aliasing generated by the sampling of a hologram by pixel is described. Next the high-order diffracted beams reproduced from the hologram that contains aliasing are explained. Finally, we show that the viewing zone can be enlarged by combining these high-order reconstructed beams from the hologram with aliasing.     

俄歇电子全息的计算机模拟研究和数值重现

原子的芯能级电子吸收能量后被激发 ,经过退激发过程发射出的俄歇电子波在传播过程中被周围的原子散射 ,带有周围原子结构信息的散射波 (物波 )与未被散射的电子波 (参考波 )相干涉形成的衍射图即俄歇电子全息图 ,通过全息图的重现 ,可获得原子级分辨率的三维结构信息。本文在合理的物理模型下 ,以Cu单晶以及高温超导YBCO中的Y原子近邻的一些原子簇为计算实例 ,首次就受激原子周围单层近邻原子散射和多层原子散射产生的俄歇电子全息进行了计算机模拟和数值重现 ,获得了三维晶格结构参量 ,并讨论了不同原子序数的原子在全息图形成及重现中的作用。本工作有助于材料微结构的研究     

Wavelength selection for true-color holography

We discuss wavelength selection for true-color holography by investigating the sampling nature of the holographic process. During holographic recording the chosen wavelengths point sample the surfacereflectance functions of the objects in a scene. To understand the effect of this sampling on color perception, we study the tristimulus values of points in the reconstructed hologram. The sampling results in the holographic process being mathematically equivalent to integral approximations for the tristimulus integrals. By selecting efficient approximations, we infer wavelengths to use in color holography. Our analysis not only suggests wavelengths for the usual three-color holography but also suggests the use of four or more wavelengths to improve color reproduction in holography.     

基于支持向量回归外推的统计最优近场声全息研究

通过数值仿真方法,研究统计最优近场声全息中全息面孔径大小对重建精度影响。结果表明当全息面孔径大于重建面孔径2个采样间隔便能获得较高的重建精度,再继续增大全息面孔径也可以提高重建精度,但是趋势变缓。在此基础上,进一步提出了一种利用支持向量回归对全息面孔径进行外推的方法,在不增加测量孔径的前提下,可以通过数据外推增大全息面孔径,提高重建精度。对方形简支钢板辐射声场的仿真结果,验证了方法的有效性。     

Color transmission analysis of color computer-generated holography

A color transmission approach between a computer display and a color computer-generated holography (CCGH) colorimetric system is proposed based on color matching theory. Firstly, the conversion between color quantities of a computer display and a CCGH colorimetric system is discussed based on color matching theory. Secondly, the isochromatic transfer relationship of color quantity and amplitude of the object light field is proposed. Thirdly, the color object light field was encoded into a hologram, and then the hologram was reconstructed numerically. The simulation results demonstrate that our novel approach is feasible.     

Sampling and processing for compressive holography [Invited

Compressive holography applies sparsity priors to data acquired by digital holography to infer a small number of object features or basis vectors from a slightly larger number of discrete measurements. Compressive holography may be applied to reconstruct three-dimensional (3D) images from two-dimensional (2D) measurements or to reconstruct 2D images from sparse apertures. This paper is a tutorial covering practical compressive holography procedures, including field propagation, reference filtering, and inverse problems in compressive holography. We present as examples 3D tomography from a 2D hologram, 2D image reconstruction from a sparse aperture, and diffuse object estimation from diverse speckle realizations.