彩色全息图的计算机产生和数字再现

提出了一种基于色彩合成以及菲涅尔衍射原理,用计算机产生全息图并用数字方法再现彩色全息图的方法。该方法的第一步是将物体的彩色RGB图像分离为三基色强度图,再利用博奇编码的方法制成修正离轴参考光分色计算机全息图;第二步是分别对分色全息图在频域进行调制以实现用原参考光真实再现原始物光波。通过滤波消除零级衍射及共轭像的影响,获得了所需要的实像并提高了像质。提供的实验是选用一幅RGB图像作为原始物体,给出了用博奇编码法制成的全息图以及最后经色彩合成获得的再现像。结果表明,该方法能使各分色全息图的再现像准确重合,解决了在色彩合成时容易出现的色串扰问题。     

垂直分割视场制作合成动态全息图

从理论上及实验上分析了利用垂直视场分割法制作合成动态全息图的方法。将二步彩虹全息术中的主全息图Ｈ１分成若干全息单元,在各单元中分别记录了物体一系列连续变化状态的二维图像,利用该主全息图制作像面全息图Ｈ２,从而获得合成动态全息图。该方法用银盐干版记录主全息图Ｈ１,节省了大量的曝光时间。     

合成全息图常见图像畸变问题的分析

合成全息图存在特殊的图像畸变问题。以研究图像畸变问题为目的,分析了场景采样、全息图记录、再现系统的几何关系,提出了该畸变问题产生的原因,解释了造成的影响,并简要讨论了一些改进方法。     

乙醇喷雾场粒子尺寸和速度的数字全息测量

利用连续波激光器和高速CCD,采用数字同轴全息系统,记录了乙醇喷雾粒子场全息图.对粒子场再现像进行聚焦像合成,自适应滤波、二值化、Roberts边缘提取,Hough变换和亚像素精度计算,得到粒子的直径和位置信息.利用两次曝光记录的两个序列全息图得到粒子位移,进而求得粒子的运动速度,给出了实验结果.研究结果表明,该实验系统可用于内燃机喷雾场测量,且具有光路系统简单、成本低等特点.     

数字合成彩虹全息图

提出了一种利用现代计算机技术制作全息图的新方法。数字彩虹全息图是计算机技术、数字图像处理技术应用到传统的合成全息图制作技术中的一种全息图。把用数码设备采集到的图像或利用计算机生成的图像作为全息拍摄的“物”,突破了传统全息只能拍摄实物的限制,实现了全息图制作的数字化。实验结果表明了该方法的可行性。同时也讨论了该方法的优越性及在实际应用中的重要意义。     

动态数字彩虹全息显示的研究

提出一种动态数字彩虹全息显示术,该技术将计算机制全息术和动态双视彩虹全息合成术相结合,根据彩虹全息的基元全息图为“线全息图”以及双眼立体视觉的特点,计算物点的线全息图上两个片断,使得两个全息图片断分别对应左右眼视图,同时对彩虹全息图的狭缝像进行横向分割,使得不同区域成为物体不同姿态的视窗,从而达到动态显示的效果.给出了数字动态全息的计算方法,并得到了初步的实验结果.     

利用合成谱在计算全息图中编码多个物体的方法

 提出在迂回位相傅里叶变换计算全息图中利用合成谱记录多个物体的方法。该方法利用多个物体合成的傅里叶频谱,代替传统的迂回位相型计算全息图中的单一频谱,在一幅计算全息图中完成多个物体的编码。再现时多个物体同时再现在同一衍射级的周围,并且再现像的形式可以多种多样。采用液晶空间光调制器(LC SLM)完成计算全息图的光学再现,实验验证了方法的有效性。结果表明：该方法可有效提高计算全息图的信息容量。     

全视差合成全息图的激光直写拍摄

为了实现可白光下再现的全视差拼接合成全息图,结合图像处理技术、合成全息图的原理,提出一种激光直写拍摄技术.实验得到了具有57°的较大观察视场的数字合成全息图,并实现了1×1m2大面积拼接.     

双视三维动态反射全息图合成技术研究

在综合了白光反射全息、像全息、体视对全息和合成全息等多种技术的基础上 ,提出了一种制作双视三维动态反射全息图的合成技术 ,给出了制作该类全息图有关参数的设计方法 ,成功地制作了一种适于近距离观察的双视三维动态反射全息图样品 ,有效消除了用双眼观察普通动态全息图时常出现的像混淆现象 ,其清晰的三维立体图像、生动而逼真的动态艺术效果 ,具有较高的艺术欣赏和防伪价值 ,为该类全息产品的开发探索了一条可行途径     

基于离散Fourier变换的内源全息图重构计算方法

对基于离散Fourier变换的内源全息图重构计算方法作了深入系统的分析，讨论了如何计算整个球面全息图对原子重构像的贡献，克服了以往该方法只能计算半个球面全息图的不足，并运用采样定理知识，分析了全息图的采样率、重构像的空间范围和分辨率等问题. 关键词： 内源全息术 离散Fourier变换 采样定理 同步辐射     

Joint approach of the sub-holograms in on-axis lensless Fourier phase-shifting synthetic aperture digital holography

In on-axis lensless Fourier phase-shifting synthetic aperture digital holography, to compose all of the phase-shifting sub-holograms to a large synthetic aperture digital hologram effectively, firstly, the cross-correlation algorithm of the object waves is presented to correct the joint misplacement of the sub-holograms. Secondly, to make the phase-shifting synchronization matching of different sequence phase-shifting holograms, the cross-correlation algorithm of the phase-shifting holograms is employed. Compared with the traditional cross-correlation algorithm of the sub-holograms, the proposed approach makes the joint precision of the sub-holograms reach sub-pixel accuracy, and the resolution of the reconstructed image is improved significantly. In general, the proposed approach is effective in restraining the quality degradation of the synthetic reconstructed image that comes from the joint misplacement of the sub-holograms and the phase-shifting non-synchronization of the phase-shifting holograms.     

Digital particle holographic system for measurements of spray field characteristics

A digital particle holographic system for measurements of spray fields is presented. A double exposure hologram recording system with a synchronization system for time control is established, resulting in digital holograms that can be quickly recorded. To process recorded holograms, the correlation coefficient method is used for focal plane determination of particles. To remove noise and improve the quality of holograms and reconstructed images, a Wiener filter is adopted. The two-threshold and image segmentation methods are used for binary image transformation. For particle pairing, the match probability method is adopted. The proposed system is applied to a spray field, and three-dimensional velocities and sizes of spray droplets are measured. Measurement results from the digital holographic system are compared to those made by laser instruments, which prove the feasibility of the proposed in-line digital particle holographic system as a good measurement tool for spray droplets.     

长工作距离显微成像数字全息合成孔径方法(英文)

提出了一种用于长工作距离下显微成像的数字全息合成孔径方法。首先,在不同斜入射照明条件下记录多幅包含不同物光频谱范围的数字全息图。然后,利用每一幅全息图通过数字方法重构并放大物体强度像。最后,通过非相干叠加这些强度像得到分辨力提高且散斑噪声减小的合成物体强度像。理论分析和实验结果表明,此方法可应用于长工作距离下的原位显微观测。     

A strong adaptable autofocusing approach of off-axis infrared digital holography under different quality conditions of holograms

In this paper, we present an innovative autofocusing criterion for the reconstruction of infrared digital holograms. This criterion has the advantages of fast, efficient and precision when determining the reconstruction distance of off-axis digital holography. This criterion is a mean-free high frequency calculation process. We focus on the problem of mean value drifting found in previous published methods and design our new approach to solve it. Unlike the previous methods perform well only with high quality holograms, our method is effective for both high and low quality holograms. Even when hologram is degraded by destructive interference, our method still performs well. This method helps to automatically determine the precise reconstruction distance, and we are sure that this technology can be applied in industrial applications in the future.     

Optical retrieval of encrypted digital holograms for secure real-time display

Secure data transmission by use of encrypted digital holograms and an optical retrieval system for secure real-time display are proposed. Original images are encrypted by a double-random phase encryption technique and then are recorded as digital holograms in a CCD, together with a reference plane wave. This digital hologram of the encrypted image can be transmitted to receivers via any conventional electronic or digital communication channels. The decryption key is also recorded as a digital hologram. At the receiver, the original image can be retrieved by an optical correlation-based reconstruction process. Both encryption and retrieval can be performed by all-optical means, and thus a real-time secure display can be implemented. We demonstrate the proposed system numerically and experimentally.     

Spatial-frequency-filtering effect of multiphase holograms

A well-designed hologram can be used as a spatial frequency filter to remove moiré fringes in a digital imaging system. However, it also degrades the resolution of the image. We have used a homemade program to design holograms with better filtering characteristics. We have designed holograms with two, four, eight, and 16 phases and compared their diffraction efficiencies and modulation transfer functions (MTFs). The four-phase hologram showed a diffraction efficiency and MTF characteristics similar to those of the binary hologram. The eight-phase hologram, however, showed much better diffraction efficiency than the previous two, and thus higher MTF values. The 16-phase hologram was still better, but the improvement was marginal. We have manufactured binary and eight-phase holograms and measured their MTFs. We have also observed directly their filtering effects by attaching them to a digital camera and taking pictures of test charts. The Moiré-fringe-removing effects of the two holograms were similar, but the eight-phase hologram showed better resolution.     

Securing complex and multi-plane data in a lens-less digital holographic information system that uses position-phase-shifting geometry

A digital holographic information system can process complex three-dimensional (3-D) object information. We demonstrate a scheme for securing complex and 3-D information in the context of in-line digital holography. Double random phase encoding in the free-space propagation domain of light is used to secure the complex information. Encrypted in-line digital holograms are recorded using the position-phase-shifting method. The encrypted complex image at the CCD recording plane is retrieved from the real-valued digital holograms, and is used for decryption. The robustness of the method has also been studied for various securing keys used in the method against blind decryption. A layer-by-layer information retrieval from the encrypted digital hologram is also discussed. The method can also be used to secure digital complex information in a virtual optics modality using holographic principles.     

Phase retrieval from double axially displaced holograms for dual-wavelength in-line holography

A phase retrieval method for dual-wavelength in-line digital holography is presented with double axially displaced holograms.A synthetic wavelength is used during iterative propagations to retrieve wrap-free phase distributions with a much extended measurement range.The simulation and experimental results demonstrate a better elimination of the twin image,a faster rate of convergence of the iterative routine and less number of wavelengths are compared with previously reported multiple-wavelength in-line holography.     

Transient vibration measurements using multi-pulse digital holography

An optical system for the evaluation of transient deformations will be described. In order to increase the temporal resolution, a ruby laser producing four pulses has been used. Four separate digital holograms (one hologram for each pulse) of the test object are recorded in a few microseconds on three CCD sensors. The Fourier method is used for the quantitative evaluation of the digital holograms. The phases are obtained from the complex amplitudes, and the deformation at different times is calculated from phase subtraction. Experimental results are presented.