Interferometric key readable security holograms with secrete-codes

A new method is described to create secrete-codes in the security holograms for enhancing their anti-counterfeiting characteristics. To imitate these codes is difficult as pure phase objects having complex phase distribution function are used to modulate the object beam that is recorded in conjunction with an encoded interferometric reference beam derived from a key hologram. Lloyd’s folding mirror interferometer is used to convert phase variations of the reconstructed wave-front into an intensity pattern for hologram authenticity verification. Creating the secrete-codes through an interferometric reference beam from the key hologram facilitates a multi-stage authenticity verification as well as easy repositioning of the security hologram through a specific Moiré pattern generated during the verification process.      

Dual beam encoded extended fractional Fourier transform security hologram with in-built repositioning

This paper describes a simple method for making dual beam encoded extended fractional Fourier transform (EFRT) security holograms. The hologram possesses different stages of encoding so that security features are concealed and remain invisible to the counterfeiter. These concealed and encoded anticounterfeit security features in the security hologram can only be read through a key hologram. Key hologram also facilitates in-built repositioning of security hologram. The method of fabrication, the principle of reconstruction and the experimental results are presented.      

Multiple information encryption by user-image-based gyrator transform hologram

A novel multiple information encryption by user-image-based gyrator transform hologram is proposed. In encryption process, each channel of the user image is phase encoded, modulated by random phase function and then gyrator transformed to get the gyrator spectrum of user image. Subsequently, each channel of the secret image is normalized, phase encoded, multiplied by modulated user image, and then gyrator transformed to obtain the gyrator spectrum of secret image. The encrypted digital hologram is recorded by the interference between the gyrator spectrum of user image and the spherical wave function. Similarly, the digital hologram for decryption is recorded by the interference between the gyrator spectrum of secret image and the spherical wave function. The multiple encrypted digital holograms are multiplexed into a final encoded hologram and the corresponding digital holograms for decryption are multiplexed into a final hologram for decryption. The wavelength and radius of the spherical wave function, and angle of gyrator transform are all essential keys for decryption. The proposed system has two main features. First, the encrypted hologram has no information about secret image. Second, the hologram for decryption used as identification key. Consequently the two marked security layers of information protection are achieved. The proposal can be realized by optoelectronic system. Numerical simulation results demonstrate the feasibility and security of the proposed technique.     

Concealed moiré pattern encoded security holograms readable by a key hologram

This paper describes a novel method of incorporating concealed coding features in security holograms in the form of moiré patterns, which need an encoded key hologram to decode them. These concealed codes in the holograms are in turn recorded with an encoded feature, so that these remain invisible to the counterfeiters thereby enhancing the anti-counterfeiting ability of security holograms. These security features, which are specific kinds of moiré patterns, can only be decoded by using an encoded key hologram in the final reading process. Though these type of security holograms are quite suitable for visual inspection, they possess high degree of anti-counterfeit ability and also do not require expensive reading machines. They can also be used as security codes for better protection against counterfeiting embossed holograms. Two different recording schemes for the formation of such security holograms and typical experimental results have been presented.     

Securing information by use of digital holography

An information security method that uses a digital holographic technique is presented. An encrypted image is stored as a digital hologram. The decryption key is also stored as a digital hologram. The encrypted image can be electrically decrypted by use of the digital hologram of the key. This security technique provides secure storage and data transmission. Experimental results are presented to demonstrate the proposed method.     

二次再现全息图

目前 ,光学防伪技术已广泛应用于钞票、信用卡、各种证件和高档商品上。全息术是一种被广泛认知的光学防伪技术 ,编码加密技术是提高它防伪功能的重要手段。二次再现全息图是根据全息图能够进行多次记录和多次再现的特点提出的一种加密全息图。在一定的照明条件下 ,它的再现光经过一个平面反射镜的反射返回到全息图 ,作为它的第二束照明光 ,这时能够再现出被加密的图像。它是由一个像全息图和一个参考光编码全息图组合而成的。一般情况下 ,二次再现全息图存在再现光路恢复困难的问题。利用低频光栅能够较好地解决这一问题 ,使二次再现全息图达到实用性的要求。该技术用于防伪产品可提高它的防伪力度。给出了详细的理论分析、制作方法和实验结果     

Fast Optimization of Binary Encrypted Hologram Based on Error Correction Method in Optical Security Systems

In practical optical security systems we must consider various circumstances for reading and decrypting encrypted holograms. Binarization of the hologram is best suited for such applications because of the ease of handling encrypted data. However, the decrypted image is greatly degraded by binarization. Therefore, optimization of a binary hologram is essential in using such a technique. In this paper, we propose a fast optimization method of a binary encrypted hologram to obtain a good reconstruction based on the error correction algorithm. In the proposed method, multiple pixels of the binary hologram are simultaneously flipped for the optimization according to the priority for the correction. The time for the optimization is only 3% of that of the simulated annealing method.     

基于相位恢复和数字全息的音频水印

提出了一种在数字全息技术中引入相位恢复算法的音频水印方法.用水印图像经相位恢复处理形成虚拟物光波与参考光波干涉,得到高对比度的傅里叶变换全息图.利用量化算法和离散余弦变换把数字全息图嵌入音频信号中,在水印提取过程中不需要原始音频信号的参与,并且采用密钥加强了水印的安全性.数值计算实验表明:该算法对有损压缩、重采样、低通滤波、噪音干扰等常用音频信号攻击均具有很好的稳健性.     

基于数字全息及离散余弦变换的图像数字水印技术

提出了一种以数字全息和离散余弦变换为基础的数字水印技术,实现了在原始图像中嵌入数字全息水印。考虑到数字全息图的不可撕毁性,使得数字全息水印本身就具有良好的抗剪切能力,并且与传统的二维灰度水印相比嵌入的信息更多。数字全息图通过傅里叶变换全息的方法获得,为了提高抗有损压缩能力,在数字全息水印嵌入过程中采用了基于(JPEG模型和分解离散余弦变换(DCT)系数的方法。实验表明,通过该算法获得的数字全息水印对JPEG有损压缩和剪切等图像处理操作均有很好的稳健性,并且采用密钥加强了水印的安全性。因此该算法能成为数字多媒体产品版权保护的有效方案。     

Cascaded Fresnel holographic image encryption scheme based on a constrained optimization algorithm and Henon map

We propose an image encryption scheme using chaotic phase masks and cascaded Fresnel transform holography based on a constrained optimization algorithm. In the proposed encryption scheme, the chaotic phase masks are generated by Henon map, and the initial conditions and parameters of Henon map serve as the main secret keys during the encryption and decryption process. With the help of multiple chaotic phase masks, the original image can be encrypted into the form of a hologram. The constrained optimization algorithm makes it possible to retrieve the original image from only single frame hologram. The use of chaotic phase masks makes the key management and transmission become very convenient. In addition, the geometric parameters of optical system serve as the additional keys, which can improve the security level of the proposed scheme. Comprehensive security analysis performed on the proposed encryption scheme demonstrates that the scheme has high resistance against various potential attacks. Moreover, the proposed encryption scheme can be used to encrypt video information. And simulations performed on a video in AVI format have also verified the feasibility of the scheme for video encryption.     

Binary computer-generated holograms for security applications from a synthetic double-exposure method by electron-beam lithography

We have developed a new multiplexing method for producing binary computer-generated holograms (CGH's) for security applications. This method is based on double recording of two types of coding method upon binary CGH's. The CGH synthesized by the proposed method can have multiple image planes from the region close to the hologram (image region) to infinity (Fraunhofer region) without severe degradation of reconstructed images in the image region. A CGH containing simultaneous image- and Fourier-type holograms is fabricated by electron-beam lithography. Some experimental results are presented.     

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     

数字全息技术中散斑噪声滤波算法比较

 在数字全息测量记录过程中,其所记录的全息图易受到散斑噪声的污染造成分辨率下降,同时也严重影响数字全息再现的效果,因此研究适用于数字全息技术中散斑滤波的算法具有重要的实用价值。介绍了中值滤波、Lee滤波、Kuan滤波和SUSAN滤波这四种常用的散斑滤波算法,并将它们运用于数字全息实验所记录图像和数字再现图像的散斑噪声滤波处理中,然后对这四种算法的处理结果进行评价。结果表明,在数字全息技术中使用SUSAN滤波算法进行处理,既明显抑制了散斑噪声,又有效保证了再现图像信息的完整性。     

三维物体多重菲涅耳计算全息水印与无干扰可控重建方法

提出了一种基于三维物体的多重菲涅耳计算全息水印方法.将水印信号作为虚拟三维物体的层面,首先结合分区复用层析法和菲涅耳双随机相位编码方法产生复噪声形式的水印信号;然后对水印信号的频谱作共轭对称处理实现实值编码;为减小对宿主全息图数字重建的影响,将水印信号的频谱设置于对宿主数字重建影响小的频谱非感兴趣区域;编码后的信号以一定强度叠加于宿主全息图,水印信号恢复无需原始宿主全息图信息,可实现盲提取,对宿主全息图重建像面的二维码可扫描识别.仿真测试结果表明,所提出的方法具有较好的透明性和稳健性,在宿主全息图遭受滤波、JPEG(联合图像专家小组)压缩、高斯噪声、剪切、旋转等各种攻击的情况下,不论对宿主还是水印信号仍具有良好的数字重建质量,对重建像面的二维码仍可扫描识别;而重建像面水印信号的无干扰可控重建后处理操作解决了不同层面水印信号之间的衍射干扰问题,提高了水印信号的重建质量.虚拟光学手段的应用丰富了水印信号设计方法并提升了算法的安全性.     

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。     

Optical Security System Based on the Biometrics Using Holographic Storage Technique with a Simple Data Format

We implement a first practical holographic security system using electrical biometrics that combines optical encryption and digital holographic memory technologies. Optical information for identification includes a picture of face, a name, and a fingerprint, which has been spatially multiplexed by random phase mask used for a decryption key. For decryption in our biometric security system, a bit-error-detection method that compares the digital bit of live fingerprint with of fingerprint information extracted from hologram is used.     

二维彩虹全息图母版的非相干光拷贝技术

描述一种用非干光制作二维彩虹模压全息图母版的新技术。该技术用紫外灯作为记录光不原,记录系统中不用任何光学元件。记录过程不需防振条件,色彩编码 狭缝像的“彩虹版”上进行条纹复制而获得。彩虹版可以无数次重复使用,所以全息图母版的记录十分简单。该技术投资少、效率高,制出的全息图质量好,对大批量模压全息图制造有很高的实用价值。     

Single-random-phase holographic encryption of images

In this paper, a method is proposed for encrypting an optical image onto a phase-only hologram, utilizing a single random phase mask as the private encryption key. The encryption process can be divided into 3 stages. First the source image to be encrypted is scaled in size, and pasted onto an arbitrary position in a larger global image. The remaining areas of the global image that are not occupied by the source image could be filled with randomly generated contents. As such, the global image as a whole is very different from the source image, but at the same time the visual quality of the source image is preserved. Second, a digital Fresnel hologram is generated from the new image, and converted into a phase-only hologram based on bi-directional error diffusion. In the final stage, a fixed random phase mask is added to the phase-only hologram as the private encryption key. In the decryption process, the global image together with the source image it contained, can be reconstructed from the phase-only hologram if it is overlaid with the correct decryption key. The proposed method is highly resistant to different forms of Plain-Text-Attacks, which are commonly used to deduce the encryption key in existing holographic encryption process. In addition, both the encryption and the decryption processes are simple and easy to implement.     

数字无透镜傅里叶变换全息术中非傍轴及离焦像差的校正

对数字无透镜傅里叶变换全息图直接采用逆傅里叶变换进行物场的数值重建时.需要满足两个条件:第一,全息图的记录过程必须满足傍轴近似条件,否则再现过程中会产生非傍轴像差;第二,记录全息图时物平面与参考点光源到全息图记录平面的距离必须相等,否则再现过程中会产生离焦像差.理论分析了非傍轴及离焦记录条件下数字无透镜傅里叶变换全息图的灰度分布特点,并提出了相应的非傍轴及离焦像差的数值校正方法.根据实际的非傍轴或离焦记录情况.分别给所记录的数字全息图灰度分布矩阵乘以适当的非傍轴或离焦校正因子,以消除灰度矩阵中非傍轴或离焦因素的影响.然后再对校正后的伞息图灰度矩阵做逆傅里叶变换处理.即可得到准确的数字再现像.实验结果表明.该数值重建方法能够有效地消除无透镜傅里叶变换全息术中数字再现像的非傍轴像差及离焦像差,提高再现像的质量.     

一种基于二元位相加密的大信息量数字全息水印

研究了一种基于二元位相加密的大信息量数字全息水印方法,对需隐藏的水印信息用二元位相编码,然后再用2台阶位相密钥进行加密,作为水印插入宿主图像中,解码后得到了高质量的水印结果.与平面波照明数字全息水印相比,采用位相密钥数字全息水印有效地提高了水印提取的安全性和相对光学效率,并保持了对大信息量水印的提取质量,解码过程不依赖于原图像. 计算和分析了二元位相密钥的空间分布对水印信息提取质量的影响,计算结果验证了理论的正确性.