Position multiplexing multiple-image encryption using cascaded phase-only masks in Fresnel transform domain

A position multiplexing method based on the modified Gerchberg-Saxton algorithm (MGSA) and a cascaded phase modulation scheme in the Fresnel transform domain is proposed in the multiple-image-encryption framework. First of all, each plain image is encoded into a complex function using the MGSA. The phase components of the created complex functions are then multiplexed with different position parameters, and summed. The phase part of the summation result is recorded in the first phase-only mask (POM). The MGSA is applied on the amplitude part of the summation result to determine another phase only function which is then recorded in the second POM. The simulation results show that the crosstalk between multiplexed images is significantly reduced compared with an existing similar method [20]. Therefore, the multiplexing capacity in encrypting multiple grayscale images can be increased accordingly.     

Optical image conversion and encryption by diffraction,phase retrieval algorithm and incoherent superposition

In this paper, an optical encryption system is proposed based on tricolor principle, Fresnel diffraction, and phase iterative algorithms. Different from the traditional encryption system, the encrypted image of this system is a color image and the plaintext of it is a gray image, which can achieve the combination of a color image and a gray image and the conversion of one image to another image. Phase masks can be generated by using the phase iterative algorithms in this paper. The six phase masks and the six diffracting distances are all essential keys in the process of decryption, which can greatly enhance the system security. Numerical simulations are shown to prove the possibility and safety of the method.     

用多重菲涅耳衍射变换和相位密码板实现图像加密的技术

基于多重菲涅耳衍射变换和相位密码板,设计了一种新的图像加密计算方法.待加密的明文图像在多重离散菲涅耳衍射变换和相位密码板的共同作用下,变换为一个具有随机码特征的密文矩阵;衍射距离和相位密码板是主要的密钥.只有当所有密钥都正确时,才能成功地解密密文.结果表明,该加密算法能抵抗JPEG有损压缩、图像剪切、重度噪音污染和重采样等攻击,因此该法具有较强的鲁棒性;由于很难破解多重密钥,所以该算法具有极高的安全性.     

Color image encryption by using Arnold transform and color-blend operation in discrete cosine transform domains

A color image encryption algorithm is designed by use of Arnold transform and discrete cosine transform (DCT). The RGB components of the color image are scrambled by Arnold transform at the aspect of pixel sequence. The scrambled RGB components are exchanged and mixed randomly under the control of a matrix defined by random angle. DCT is employed for changing the pixel values of color image. In this encryption scheme the operations mentioned above are performed twice continuously. The parameters of Arnold transform and the random angle serve as the key of the color image encryption method. Some numerical simulations are made to test the validity and capability of the color encryption algorithm.     

Asymmetric optical cryptosystem for color image based on equal modulus decomposition in gyrator transform domains

An enhanced asymmetric cryptosystem for color image is proposed by using equal modulus decomposition (EMD) in the gyrator transform domains. In this scheme, the EMD is performed to create the effective trapdoor one-way function. Moreover, to enhance the security of the cryptosystem, the Baker mapping is considered and utilized for scrambling the RGB components of the color image. The parameters in the Baker mapping and gyrator transform can be served as the extra keys of the entire cryptosystem. Various types of attacks are considered in the robustness analysis experiments. Some numerical simulations are made to verify the validity and capability of the proposed color encryption algorithm.     

An optical image cryptosystem based on Hartley transform in the Fresnel transform domain

A novel method for image encryption and decryption based on Hartley transform in the Fresnel transform domain is presented. Different from the conventional method which requires lens to perform the Fourier transform for achieving Hartley transform, the proposed new optical architecture of Hartley transform is based on the Fresnel diffraction which requires no Fourier transform lenses. The position coordinate as well as the wavelength in the Fresnel transform is used as encoding keys that can ensure the sufficient information security. The main advantages of this proposed image security system are that it uses fewer optical devices and the decryption scheme is straightforward and more secure than the previous works.     

Compressive optical image watermarking using joint Fresnel transform correlator architecture

A new optical image watermarking technique based on compressive sensing using joint Fresnel transform correlator architecture has been presented. A secret scene or image is first embedded into a host image to perform optical image watermarking by use of joint Fresnel transform correlator architecture. Then, the watermarked image is compressed to much smaller signal data using single-pixel compressive holographic imaging in optical domain. At the received terminal, the watermarked image is reconstructed well via compressive sensing theory and a specified holographic reconstruction algorithm. The preliminary numerical simulations show that it is effective and suitable for optical image security transmission in the coming absolutely optical network for the reason of the completely optical implementation and largely decreased holograms data volume.     

Single-channel color image encryption using phase retrieve algorithm in fractional Fourier domain

A single-channel color image encryption is proposed based on a phase retrieve algorithm and a two-coupled logistic map. Firstly, a gray scale image is constituted with three channels of the color image, and then permuted by a sequence of chaotic pairs generated by the two-coupled logistic map. Secondly, the permutation image is decomposed into three new components, where each component is encoded into a phase-only function in the fractional Fourier domain with a phase retrieve algorithm that is proposed based on the iterative fractional Fourier transform. Finally, an interim image is formed by the combination of these phase-only functions and encrypted into the final gray scale ciphertext with stationary white noise distribution by using chaotic diffusion, which has camouflage property to some extent. In the process of encryption and decryption, chaotic permutation and diffusion makes the resultant image nonlinear and disorder both in spatial domain and frequency domain, and the proposed phase iterative algorithm has faster convergent speed. Additionally, the encryption scheme enlarges the key space of the cryptosystem. Simulation results and security analysis verify the feasibility and effectiveness of this method.     

Computer simulation of Fresnel diffraction from rectangular apertures and obstacles using the Fresnel integrals approach

In this paper, we describe a new computer simulation technique of generating Fresnel diffraction images from rectangular apertures of arbitrary dimensions by using Fresnel integrals instead of the more common fast Fourier transform methods. The simulation can be performed in almost any PC using the software MATLAB. Diffraction images can be generated for any wavelength of light and for any aperture–screen and aperture-source distances. Images for rectangular obstacles can also be simulated. Details of the algorithm and program are presented, as well as the interesting insights than can be gained from using the program. Finally, it is shown that the simulated images reduce to the simple Fraunhofer diffraction patterns for certain limiting situations.     

Optical color image encryption based on the wavelength multiplexing using cascaded phase-only masks in Fresnel transform domain

A novel technique, based on a modified Gerchberg–Saxton algorithm (MGSA) in the Fresnel-transform (FrT) domain, is proposed to encode a color image into three phase-only functions (POFs) for three separated channels: red (R), green (G), and blue (B). The decomposed three RBG channels can avoid the interference of crosstalks efficiently. In proposed decryption process, a color image can be promptly reconstructed by summing of the three decrypted RGB images after the created three POFs which are decrypted one by one. In this paper, all the created three POFs and the system parameters of FrT can be used as the keys for increasing security that are also demonstrated. The computer application simulations to the partial color encryption and decryption are given to validate the feasibility of the proposed scheme.     

基于分频域和菲涅耳域的光学图像加密方法

结合分数傅里叶变换及菲涅耳变换,在光学图像加密系统中分别具有多密钥性和无透镜性的优点,提出了基于分频域和菲涅耳域的光学图像加密方法。基于分数傅里叶变换的光学加密系统,引入菲涅耳变换及全息技术,使原有的加密系统在不增加光学元件的基础上提高了系统的安全性。理论分析和计算机仿真模拟证明了这种方法的可行性。     

A novel color image encryption scheme using alternate chaotic mapping structure

This paper proposes an color image encryption algorithm using alternate chaotic mapping structure. Initially, we use the R, G and B components to form a matrix. Then one-dimension logistic and two-dimension logistic mapping is used to generate a chaotic matrix, then iterate two chaotic mappings alternately to permute the matrix. For every iteration, XOR operation is adopted to encrypt plain-image matrix, then make further transformation to diffuse the matrix. At last, the encrypted color image is obtained from the confused matrix. Theoretical analysis and experimental results has proved the cryptosystem is secure and practical, and it is suitable for encrypting color images.     

级联菲涅尔衍射光学图像安全系统

计算机模拟验证了系统用于光学图像加密和隐藏的可行性.理论分析揭示了本系统面向应用的三个性质：相位分布的台阶数可以作为系统设计的自由度;增加系统衍射级次可以提高秘密图像的解密质量,但此时系统受到波长微变的影响也较显著;轴向位移也会产生噪音信号,其衍射距离越长,解密质量越差.     

用菲涅耳理论研究衍射光路可逆性

 用菲涅耳衍射理论研究了光栅及双光栅成像系统衍射光路的可逆性。首先用菲涅耳衍射理论分析单片光栅衍射光的复振幅分布,根据其复振幅分布的相位关系研究其可逆性;再根据单片光栅衍射光路所具有的结论来分析双光栅衍射成像效应的衍射光路可逆性,得到了光栅衍射光路及双光栅成像系统光路具有部分可逆性;应用衍射光路的部分可逆性诠释了双光栅成像效应的本质及光栅的汇合光谱特性是色散光谱特性的逆效应,并根据衍射光路具有部分可逆性的特性实现了图像处理。     

相位型波带板应用于大尺度X射线源成像的分析与模拟

针对大尺度物体的keV-X射线高分辨成像,分析了相位型菲涅耳波带板(FPZP)对物平面1mm区域内点源的成像,确定像的空间分布具有不变性,提出了一种FPZP对扩展光源成像的计算方法.使用这一方法,模拟了放大倍数为10的典型实验条件下最外环宽0.35 μm的FPZ对扩展单色光源的成像.结果表明,随着扩展光源尺度的增加,像的对比度降低.FPZP的负1级和0级衍射是导致像的背景增强和对比度降低的主要因素,并相应导致成像对物方的空间分辨能力下降.对于强度空间分布为正弦调制、对比度为1的1mm尺度方形光源,像的对比度低于0.4,物方分辨能力为0.75 μm.     

用菲涅耳衍射理论分析双光栅成像效应

从理论上对双光栅成像效应现象进行研究,分别从菲涅耳衍射理论和平面透射光栅的菲涅耳衍射公式出发,分析了物光波经过两个平行放置的平面透射光栅组成的系统衍射后的复振幅分布。分析结果表明,在理想状态下,当两个光栅的放置位置满足一定条件时,在第二个光栅后面可以观察到一个清晰的原物体图像。理论分析解释了两个光栅在双光栅成像效应中的作用,得到了双光栅成像效应发生时,两个光栅的空间频率、衍射光级数以及光栅放置位置之间的关系式,这与实验所得结果相一致。     

Image fusion by color texture extraction

In this paper, we present a method to extract shape and color information simultaneously of a colorful object by projecting sequentially sinusoidal fringe patterns onto object's surface. Distorted fringe patterns are captured by digital CCD color camera. It is applied the phase shifting method to evaluate the phase of the projected fringes. We obtain both topography details and color texture information.     

Diffracted wavefield by an arbitrary aperture from Maggi-Rubinowicz transformation: Fresnel approximation

The major purpose of this paper is to establish a general and explicit formula for calculating diffracted wavefield from Maggi-Rubinowicz transformation under Fresnel approximation. It is demonstrated that solution expression, always involves Fresnel integrals. The 2-D integration (Rayleigh-Sommerfeld or Helmholtz-Kirchhoff integral formulas) is so reduced to a 1-D integration over the rim of the aperture, with advantage of this approach in numerical evaluations.     

圆孔的菲涅耳衍射

得到了圆孔菲涅耳衍射光强分布的表达式,此式由贝塞尔函数的数列(或Lommel函数)给出,因此很容易利用普及的数学软件算出结果.并且利用CCD照相机量度了衍射光强分布,与运算的结果作了比较,也与Burch在1985报导的结果作了比较.