优化的两步相移算法在图像加密中的应用研究

优化了此前提出的两步相移算法,仅通过两幅去除背景光强(或抑制直流分量)后的干涉图数据和一个(0,π)区间的相移值,就可以成功再现出原始物波场信息,无需借助于物光光强、参考光光强等其他辅助测量信息.与菲涅耳域的双随机相位编码技术结合,该优化算法可以应用于图像加密方案中,通过计算机仿真实验验证了所提方案的可行性,并对几何密钥的灵敏度进行了测试分析.     

An encryption scheme based on phase-shifting digital holography and amplitude-phase disturbance

In this paper, we propose an encryption scheme based on phase-shifting digital interferometry. According to the original system framework, we add a random amplitude mask and replace the Fourier transform by the Fresnel transform.We develop a mathematical model and give a discrete formula based on the scheme, which makes it easy to implement the scheme in computer programming. The experimental results show that the improved system has a better performance in security than the original encryption method. Moreover, it demonstrates a good capability of anti-noise and anti-shear robustness.     

一种实现单步相移无透镜傅里叶同轴数字全息的倒频谱技术

在数字全息技术中无透镜傅里叶同轴数字全息具有高分辨,再现速度快等优点,因此有着广泛的应用前景,但它也存在再现像与直透光场及其共轭像重叠,较难分离的缺点。针对这一问题,在分析了无透镜傅里叶同轴数字全息图记录和再现原理的基础上,提出了单步相移倒频谱技术,并在理论上分析了该技术对分离出清晰再现像的可能性和该技术适用的关键条件。通过仿真实验进行了验证,结果表明:单步相移倒频谱技术能够较好地解决无透镜傅里叶同轴数字全息技术中再现像与直透光场及其共轭像重合这一困难,得到清晰的再现像;同时给出了实际实验中单步相移倒频谱技术能够适用的条件参数,这为后面的进一步实验提供了参考依据。     

相移数字全息子图拼接研究

 将全息图拼接技术应用到相移数字全息术中,改善再现像的质量。用全息图强度相关原理进行全息图拼接,再通过标准四步算法对拼接后的全息图进行运算,恢复原始物光。作为对比,对没有拼接的全息图进行了同样的操作。计算机模拟实验证明该全息图拼接技术可明显提高再现像的质量。同时,通过对光学实验获得的全息图进行零填充和拼接对比研究证明,前者只能提高系统成像的细节显示能力,后者能够提高再现像的分辨率和视场大小。     

两步广义相移干涉术的光学实验验证

提出了一种基于两步广义相移干涉术的波前再现技术以及基于衍射场统计特性的未知相移值提取算法,并且进行了光学实验验证.该方法中可仅利用两幅干涉图及一次不需精确预设的未知相移,参照物光光强和参考光光强,即可通过计算提取真实的相移量,进而恢复出物波波前复振幅,而无需借助傅里叶谱分析或数字滤波等操作.在光学实验中,对借助于空间光调制器（SLM）的间接输入和三维漫反射物体直接输入两种情况进行了详细地研究,得到的光学实验结果验证了所提方案的有效性和可行性. 关键词： 信息光学 相移干涉术 波前再现 数字图像处理     

Full-phase image encryption by two-step phase-shifting interferometry

We have proposed a full-phase image encryption method based on double random-phase encoding in Fresnel domain and pixel random permutation (PRP) technique with the use of two-step phase-shifting interferometry (PSI) we reported recently, and verified the effectiveness of this method and its robustness against occlusion and noise attacks by a series of numerical simulations. Comparing with other similar methods, this approach can decrease the number of the interferograms to be delivered from at least three needed in ordinary PSI to only two, give much better performance of image reconstruction than amplitude-based encryption, and provide much higher security level. This method is usable for both the gray-level images and binary images, and usually the latter will lead to better results.     

Image encryption based on pure intensity random coding and digital holography technique

We propose a novel image encryption method that combines the pure intensity random encoding and the digital holography technique. A phase-shifting interferometer records both phase and amplitude information of a complex object with a CCD sensor array. The encryption is performed by placing two pure intensity random masks between the image to be encrypted and an intensity recording device. Electronic decryption can be performed with fast Fresnel reconstruction procedure. Numerical simulation results show the validity of the algorithm and an optoelectronic implementation setup is also presented.     

Image encryption based on extended fractional Fourier transform and digital holography technique

We present a new optical image encryption algorithm that is based on extended fractional Fourier transform (FRT) and digital holography technique. We can perform the encryption and decryption with more parameters compared with earlier similar methods in FRT domain. In the extended FRT encryption system, the input data to be encrypted is extended fractional Fourier transformed two times and random phase mask is placed at the output plane of the first extended FRT. By use of an interference with a wave from another random phase mask, the encrypted data is stored as a digital hologram. The data retrieval is operated by all-digital means. Computer simulations are presented to verify its validity and efficiency.     

四步相移数字全息中随机误差的抑制方法

提出一种在四步相移数字全息中消除随机相移误差及CCD噪声的方法。通过多次重复四步相移数字全息的实验过程,使得每一步的相移都有多幅全息图像与之对应,把每一步对应的多幅全息图像进行数学平均就会得到4幅全息均值图像。理论分析表明,使用这4幅全息均值图像进行数字全息的重建,可以得到精确的物光波的分布,有效地消除随机相移误差及CCD噪声的影响。计算机模拟结果表明:该方法有助于提高数字全息重建光场质量。     

Spectral holography of pico- and nanosecond optical pulses

Recording and reconstruction of pico- and nanosecond pulses have been accomplished with spectral holography. The development of spectral holography in the nanosecond time-domain was achieved while using high-spectral-resolution equipment based on a Fabry-Perot etalon with a side entrance/exit. The recognition of the shaped nanosecond light pulses was also realized.     

两步相移数字全息物光重建误差分析与校正

系统研究了两步相移数字全息干涉术中相移误差引起的波前再现误差的计算和校正方法. 基于衍射物光相位分布的随机性和振幅相位的相互独立性原理,介绍了相移数字全息中物光波前再现误差的表达形式,推导出步长为π/2的两步算法中物光重建误差的表达式. 通过进一步分析这一重建误差的结构和特点,结合物光表达式,给出了自动校正相移误差引起的波前重建误差的校正方法. 该方法无需增加测量,在未知相移误差大小的情况下,只对标准两步相移算法恢复的物光复振幅进行处理就可以实现对物光振幅和相位的同时校正. 计算机模拟结果表明,校正后可将 关键词： 相移干涉术 数字全息 物光重建 误差校正     

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.     

相移干涉术及广义相移数字全息干涉术

在基础光学框架内说明了传统的相移干涉术及近年来发展的广义相移数字全息干涉术的基本原理;前者要求特殊值等步长相移,而后者则可以采用任意未知相移值.着重介绍了广义相移干涉术中的物波恢复算法,以及基于衍射场统计特性的未知相移提取算法.从一个侧面沟通了基础光学与近代光学之间的关系.     

雾化场光学全息与数字全息联合测量

针对雾化场光学全息测量存在干板湿化学处理繁琐、再现像采集耗时的问题,提出光学全息与数字全息联合测量的方法,建立由同轴光学全息、同轴数字全息以及数字延迟信号发生器组成的测量系统,并以双孔直射式喷嘴产生的雾化场为测量对象,利用该测量系统在一次测量中同时获得雾化场的光学全息和数字全息的再现图像,两者具有很好的一致性。光学和数字再现图像相对应的视场范围分别为27.87 mm4.77 mm和27.59 mm6.67 mm,数字方式获得视场范围内单一层面再现像的时间仅为8 s,而光学方式将近1 h。结果表明,光学全息与数字全息联合测量时,通过数字全息的雾化再现图像能够对实验总体效果进行实时评估,提高了雾化场全息测量的实验效率。     

Contouring of diffused objects by using digital holography

A simple method for contouring of diffused objects by using lensless Fourier transform digital holography (LFTDH) and dual-index immersion method is presented. Depth contour interval up to minimum of 0.12 mm could be achieved without making the interference phase fringes over crowded.     

相移同轴无透镜傅里叶数字全息的分析与实验

应用菲涅耳衍射和全息理论，详细分析了无透镜傅里叶变换数字全息图的记录、再现方法和再现像的特点，分析了相移数字全息图的记录和再现方法，并进行了相应的实验验证。结果表明：直接对无透镜傅里叶数字全息图进行傅里叶逆变换可同时得到与物体完全相同的再现像及其共轭像；同轴无透镜傅里叶数字全息术能最大程度满足CCD对采样条件的要求，从而可以增大记录物体的尺寸，减小记录距离，明显提高再现像的清晰度和分辨率；相移数字全息术能有效地消除数字再现光场中的零级光场和共轭像，显著提高再现像的信噪比。条件许可时，相移同轴无透镜傅里叶数字全息术是目前解决数字全息术中再现像的分离与满足采样条件之间矛盾的最佳方法。     

A new method of aperture synthetizing in digital holography

This paper proposes a new method of aperture synthetizing in digital holography based on the principle of holography. In the new method aperture synthetizing is achieved by reconstructing each sub-hologram respectively, firstly, moving each reconstructed wave field referred to the benchmark reconstructed wave field according to the relationship between spacial motion and frequency shift, and finally splicing them by using superposition. Two different recording ways, using plane wave to record and using spherical wave to record, are analyzed, and their moving formula is deduced, too. Simulation and experiment are done. The results show that in comparison with the traditional method of aperture synthetizing in digital holography, the new method can decrease calculation and save reconstructed time obviously which has better applicability.     

基于相移干涉术的光学信息隐藏系统的软件实现

结合双随机相位编码技术与相移干涉术，提出了一种信息隐藏系统，待隐藏信息被加密到多幅干涉图数据中后。通过选取合适的权重因子，它们可以被嵌入到宿主图像中；利用特定的相移再现公式和逆菲涅耳衍射变换，可以实现隐藏信息的提取及解密．通过基于Matcom的VisualC＋＋与Matlab混合编程，设计和开发了一款信息隐藏系统软件，经过界面测试，该软件可以实现图像读取及显示、基本几何参数输入、信息加密及嵌入、信息提取及解密、鲁棒性测试等主要功能．     

Optical image encryption with redefined fractional Hartley transform

A new method for optical image encryption is introduced on the basis of two-dimensional (2-D) generalization of 1-D fractional Hartley transform that has been redefined recently in search of its inverse transform. We encrypt the image by two fractional orders and random phase codes. It has an advantage over Hartley transform, for its fractional orders can also be used as additional keys, and that, of course, strengthens image security. Only when all of these keys are correct, can the image be well decrypted. The optical realization is then proposed and computer simulations are also performed to confirm the possibility of the proposed method.     

采用短相干光数字全息术实现反射型微小物体的三维形貌测量

针对反射型微小物体，设计了一种可在三维形貌测量中实现微小物体分层记录的短相干光源无透镜傅里叶变换数字全息记录系统，并利用该系统对锥形微孔壁实现了分层记录.该系统可通过调节待测物体的位置，改变全息记录中的物光光程，从而获得重构三维物体所需要的一系列子全息图.该系统具有光路简洁，系统的附加误差小的特点.实验测量的轴向误差约为3.5%，横向误差约为2.6%.此外，在三维重构的过程中，为避免因散斑噪声较大而无法利用位相信息进行三维重构的情况，采用了最小二乘多项式拟合方法，将微小物体的一系列再现强度图像进行三维重构.由于避免了复杂的相位展开，所以不但运算简单，而且具有较强的抗散斑噪声能力.