Reconstruction of digital hologram of small particles on arbitrarily tilted plane using digital holography

Digital holographic off-axis geometry is presented for the reconstruction of the digital hologram of small particles in an arbitrarily tilted plane. A single hologram is sufficient to obtain a well focused clear image. We can't obtain clear images of small particles in the case of plane tilted to the detector plane by ordinary reconstruction method because of the rotation of the hologram plane. Rotational transformation based on coordinate rotation in Fourier space makes it possible to reconstruct holographic images on any plane in the object space. The reconstruction of digital hologram is based on the plane wave expansion of the diffracted wave fields, using Fourier optics and the two-axis rotation of the wave vectors. With this method, the object-to-hologram distance can be any small distance because the minimum distance requirement does not apply.     

The formation of large scale reconstructed images through the use of holograms

We propose and demonstrate a method which constructs large size multicolor images using a holographic technique in limited spaces, i.e., tunnels. A traffic sign image of the same size and color as an actual traffic sign board is displayed using many comparative small holograms. Each hologram is composed of a single computer generated hologram (CGH). Though it was necessary to make many CGHs, we have shortened the hologram production time by putting a reconstructed image on long distance, and using many reconstruction sources. Moreover, though cross-talk images are caused in a color reconstruction, by adjusting the optical system it is possible to make sure that drivers see only the appropriate image. Many holograms function as one big hologram, and it has been confirmed that a large reconstructed image can be displayed in a limited space.     

面向真彩色三维显示的分层角谱算法和Gerchberg-Saxton算法研究

分层角谱算法可用于三维物体全息图的生成计算,在计算时间、占用内存和算法复杂度方面占有优势.本文基于强度图和深度图的分层角谱算法,对多波长采样进行分析,有效抑制混频现象,实现了真彩色物体的计算全息图生成.针对分层角谱算法重建时产生的散斑噪声问题,引入Gerchberg-Saxton(GS)算法,提出基于分层角谱算法的GS算法.通过计算比较引入GS算法前后再现像的均方根误差和峰值信噪比,证明该算法可有效地抑制散斑噪声,提高全息图的再现像质量,更适用于复杂形貌三维物体的计算.     

利用反射全息实现计算全息三维显示

计算全息和光学全息都可应用于三维显示,但各有自己的优势和缺陷.将计算全息和光学反射全息相结合,可以突破光学全息对记录物体的限制,进行虚拟物体或自然场景的全息图的制作,同时可以实现白光再现.本文首先用三维扫描仪获得实际物体的三维数据,用"点云算法"模拟得到其菲涅耳全息图透射率数据,采用计算全息打印机将其输出于全息记录介质,得到可光学再现的菲涅耳计算全息图H1.然后将H1作为光学全息的记录物体进行反射全息记录,将平面全息转化为体全息,实现了计算全息白光再现.     

利用反射全息实现计算全息三维显示

计算全息和光学全息都可应用于三维显示,但各有自己的优势和缺陷.将计算全息和光学反射全息相结合,可以突破光学全息对记录物体的限制,进行虚拟物体或自然场景的全息图的制作,同时可以实现白光再现.本文首先用三维扫描仪获得实际物体的三维数据,用"点云算法"模拟得到其菲涅耳全息图透射率数据,采用计算全息打印机将其输出于全息记录介质,得到可光学再现的菲涅耳计算全息图H₁.然后将H₁作为光学全息的记录物体进行反射全息记录,将平面全息转化为体全息,实现了计算全息白光再现.     

Real-time optical reconstruction of the diffused 3D object using phase information calculated by Continuous Wavelet Transform

We propose the real time optical reconstruction of a three-dimensional (3D) object from a digitally recorded hologram. Phase distribution of the recorded hologram is numerically calculated by 1-dimensional Continuous Wavelet Transform (1D-CWT) for digital reconstruction with phase only information. Also, the phase distribution of 1D-CWT transferred to the spatial light modulator (SLM) is used to obtain optically reconstructed image. It is observed that an efficient real-time analysis can be achieved, if phase of 1D-CWT is used. In the same time, optically reconstructed 3D objects obtained by only phase information are about three times brighter than bleached hologram intensity's. So the minimum power loss can be obtained. Numerical and experimental results are presented.     

高速粒子场同轴Fraunhofer全息数据处理系统研究

介绍了用同轴Fraunhofer全息测量强动载下材料表面微喷射粒子场的数据处理方法.在全息像重建过程中，将再现的三维粒子场由计算机控制分成许多小薄层采集.在数据处理过程中根据图像中粒子边缘，决定在整幅图或局部采用边缘检测的方法提取大粒子，根据图像的灰度分布将图像分成很多小区域，在每个小区域采用不同的阈值分割图像.在处理结果的校正中根据粒子场的特点，去除过大、过小和重复统计粒子.采用该方法得到了粒子的空间分布图像及粒子大小的统计结果.     

基于空间光调制器的多层图像的构建与可视化研究

 为解决实时直观地观察多层再现图像的问题,提出利用发光材料实现其可视化.针对由沿光轴方向的二维图层组成的空间图像,利用高效、快速的三维Gerchberg-Saxton算法,得到位相型计算全息图,并通过计算机进行了数字模拟再现.阐述了三维Gerchberg-Saxton算法的流程,并搭建了基于液晶空间光调制器的位相全息图光学再现与可视化光路.利用液晶空间光调制器的灰度-位相曲线把计算全息图转换为灰度图,加载在液晶空间光调制器上,再现出高质量的三维光场,同时利用量子点材料的荧光特性实现了图像的可视化.实验结果表明,光学再现与计算机模拟结果较吻合.该技术在医学、军事、三维显示、微加工以及显微技术等领域有重要应用价值.     

全息模拟再现像的三维重构

提出一种全息模拟再现像的三维重构方法，可以模拟再现得到三维再现像.计算机模拟再现许多幅在不同深度位置的二维光强分布；利用灰度级变化的聚焦度评价方法，通过寻找最大聚焦度值，确定再现三维像各像点的深度信息.实验证明,该方法能实现模拟再现像的三维重构，使数字全息术有希望成为一种全新的三维面形检测技术.再现像三维重构的实现可以更客观地对全息图进行像质评价，并验证计算机制全息术算法的正确性.     

Fresnel hologram reconstruction of complex three-dimensional object based on compressive sensing

Reconstruction the computer generated Fresnel hologram of complex 3D object based on compressive sensing （CS） is presented. The hologram is synthesized from a color image and the depth map of the 3D object. With the depth map, the intensity of the color image can be divided into multiple slices, which satisfy the condition of the sparsity of CS. Thus, the hologram can be reconstructed at different distances with corresponding scene focused using the CS method. The quality of the recovered images can be greatly improved compared with that from the back-propagation method. What＇s more, with the sub-sampled hologram, the image can be ideally reconstructed by the CS method, which can reduce the data-rate for transmission or storage.     

Phase-only stereoscopic hologram calculation based on Gerchberg–Saxton iterative algorithm

A phase-only computer-generated holography(CGH) calculation method for stereoscopic holography is proposed in this paper.The two-dimensional(2D) perspective projection views of the three-dimensional(3D) object are generated by the computer graphics rendering techniques.Based on these views,a phase-only hologram is calculated by using the Gerchberg–Saxton(GS) iterative algorithm.Comparing with the non-iterative algorithm in the conventional stereoscopic holography,the proposed method improves the holographic image quality,especially for the phase-only hologram encoded from the complex distribution.Both simulation and optical experiment results demonstrate that our proposed method can give higher quality reconstruction comparing with the traditional method.     

X射线激光全息的可见光再现

Ｘ射线激光全息是Ｘ射线激光一个非常重要的应用。本文模拟了Ｇａｂｏｒ全息的记录和再现过程，分析了Ｇａｂｏｒ全息和无透镜傅立叶变换全息用可见光再现过程中再现象的放大率、象差等对再现象的影响，提出了减小象差和获得高分辨再现象的方法，认为无透镜傅立叶变换全息是当前Ｘ射线激光全息的重要记录方式。     

Tilted objects EFI extracted at once by 3D output of the angular spectrum method

Since many optical imaging systems suffer from a limited depth of focus, three-dimensional (3D) objects, or even flat objects tilted with respect to the optical axis, are imaged with only a portion of them in focus. Typically, to overcome this problem, in-focus areas are extracted from different images taken at different depths. The in-focus regions are thus merged together to build the extended focus image (EFI). In this work, we propose a quasi-automatic method for the EFI construction of tilted objects, extracted at once by 3D output of the Angular Spectrum Method (ASM) from a single digitally recorded hologram. Results show that our method can be effectively used for the correction of the anamorphism due to the reconstruction on a tilted plane with respect to the hologram one.     

三维面形测量数据的计算全息可视化

提出利用计算机制全息进行三维面形测量数据立体重现的技术。首先利用三维面形测量技术同时获取三维物体的强度和距离像；然后根据三维面形测量数据，设计和制作菲涅耳计算全息图；最后将计算全息和光学全息相结合，以菲涅耳计算全息图的光学再现像为对象，记录光学像全息。这样既解决了计算机制全息术中真实三维物体立体信息数据捕捉的问题，又为三维面形检测提供了一个行之有效的立体重构技术。给出了这种方法的原理、计算全息的设计、制作方案和实验验证结果。     

双重分数傅里叶变换计算全息

提出了双重分数傅里叶变换计算全息，在这种方法中，将两个图像的信息分别经不同阶的分数傅里叶变换后，记录在同一张分数傅里叶变换计算全息图上，它需要两个特定的分数傅里叶变换系统才能再现出所记录的图像信息，利用其再现方式的特殊性，可制成一种新的安全认证系统。     

Integral color rainbow hologram based on computer image processing

A new method for obtaining color rainbow holograms of 3D scenes using single wavelength laser is proposed and implemented by combining integral photography, computer graphics and rainbow holography. In the method, three integral photography (IP) images whose colors correspond to three primary colors are calculated by simulating integral photography, and exported on the film. By illuminating the IP images with diffused coherent beam from the opposite side, three images of the 3D scene are reproduced and overlapped on a particular image plane by the three linear micro-lens arrays. The linear micro-lens arrays can be regarded as the slits. A color rainbow hologram can be created after a single exposure by interfering the reproduced 3D images and the reference beam. Furthermore, we demonstrate experimentally the new method for a simple case and the results can be generalized in integral photography.     

Watermarking of three-dimensional objects by digital holography

We present an optical method for information watermarking of three-dimensional (3D) objects by digital holography. A hidden image is embedded by double phase encoding in a phase-shift digital hologram of the 3D object. We decode the watermarked hologram to reconstruct the hidden image and the 3D object. We use either the entire hologram or a part of it to decode the hidden image. Experiments are presented to illustrate the ability to recover both the 3D object and the decoded hidden image. Digital holograms of the 3D object are obtained by optical experiments. The watermarking process, 3D object reconstruction, and hidden image recovery are performed digitally. To the best of our knowledge, this is the first report of 3D object watermarking by use of a phase encoding technique and digital holography.     

数字全息周期像的产生机理及在抑制零级衍射上的应用

在数字全息成像中, 利用CCD的RGB模式采样全息图时, 全息重构像会出现特定的周期性分布. 本文从理论和实验上详细研究了这种周期像产生的机理、分布特性和应用. 研究结果显示, 由于CCD的光谱滤镜会使全息图的RGB三个单色采样阵列出现部分像素信号的缺失, 因此, 需要通过特定的demosaicing数学算法对缺失的像素信号进行重建以形成完整的单色采样阵列, 这是数字全息再现像周期分布产生的根源. 而基于demosaicing算法的采样阵列重建会在全息图频谱中引入调制函数, 导致物体再现像和零级衍射斑的周期分布差异. 本文揭示了全息图的RGB采样、demosaicing算法与全息重构像周期性之间的内在关联. 最后, 讨论了结合空间移位和图像形态学技术, 利用重构像的周期性抑制零级衍射斑的应用. 所有理论与实验研究结果完全一致. 关键词： 数字全息 图像周期性 零级斑抑制     

Numerical reconstruction and twin-image suppression using an off-axis Fresnel digital hologram

In this work we proposed a novel approach for the numerical reconstruction of digital holography that uses only an off-axis Fresnel digital hologram and can easily be carrying out in a personal computer. From the presented off-axis holographic principle, the reference wave accompanies to the numerically reconstructed image, also makes the separation to the zero-order and twin images. Therefore, the concept can be applied to suppress the blurring of numerical reconstruction by adding the extra reconstruction plane and the formularized numerically reference wave in the reconstruction procedure. As expected, the blurring images can be separated out and removed from the reconstructed image. Then, by performing the back propagating to the exact reconstruction plane, one can obtain the pure object image without the blurring. In contrast to the temporal phase-shifting digital holographic-based scheme that employs multiple exposures the technique can be more effectively and easily overcome the blurring problem, also provide the practical feasibility in the digital holographic application. PACS 42.40.-I; 42.30.Wb; 42.40.Ht     

多平面全息三维显示及其噪声消除研究

基于层析法和Gerchberg-Saxton迭代算法,计算得到了多个平面构成的三维物体的计算全息图,并将该计算全息图加载于空间光调制器上,获得了具备全视差的三维立体显示。基于以上方法,对灰度图像进行显示,获得了较高的像质。构建了由100个平面组成的立方体,获得了立方体的三维图像。另外,在计算全息图时附加了相位平移函数,消除了由空间光调制器的栅格结构引起的多重衍射像噪声,将能量利用效率提高到原来的379%。这样,可获得高衍射效率、高像质且具备全视差的三维全息显示。