Binary encoding method to encrypt Fourier-transformed information of digital images

An encoding method is used to encrypt the Fourier-transformed information of a hidden (covert) digital image in an overt image, while the Fourier-transformed information must be encoded with binary codes. All of the pixels in an overt image are classified into five groups that are called identification, type, tracing, dimension, and information codes. Identification codes are used to judge if the overt image contains codes that belong to the proposed encoding method or not; type codes are used to judge the encoding type; tracing codes are used to judge the encoding trace; dimension codes are used to judge the size of the hidden information; and information codes are used to decode the hidden information. Applying the proposed encoding method is rather easy, and host images corresponding to overt images are not needed for decoding work. The experiment has demonstrated four types of encoding for the proposed encoding method to reconstruct covert images without any distortion or only with a little distortion.     

Hybrid encoding method by assembling the magic-matrix scrambling method and the binary encoding method in image hiding

The magic-matrix scrambling method and the binary encoding method are combined to form a hybrid encoding method for hiding digital covert images. For this hybrid encoding method, a covert image is encoded into a host image to form an overt image. First, the magic-matrix scrambling method is used to rearrange all the pixels of the covert image by using a specified magic matrix modified from a magic square to form a scrambled matrix. Then, all the pixels of the scrambled matrix are denoted by binary data. Finally, the binary data are encoded into the host image to form the overt image. The pixels of the overt image contain nine groups of codes used for decoding the covert image, i.e. identification codes, covert-image dimension codes, scrambling-time codes, magic-square dimension codes, corner codes, shifting codes, arrangement codes, graylevel codes, and information codes. The overt image and the host image look almost the same for eyes. Furthermore, the covert image can be decoded directly from the overt image without using the host image. The most important feature is that the decoded covert image is identical to the original covert image, i.e. there is no distortion in the decoding work.     

Encrypting image by assembling the fractal-image addition method and the binary encoding method

The fractal-image addition method and the binary encoding method are assembled to form a hybrid method for encrypting a digital covert image. For this hybrid method, a host image is used to create an overt image with the information of the covert image. First, the fractal-image addition method is used to add some fractal images and the covert image to form an image-mixing matrix. Then, all the pixel values of the image-mixing matrix are transferred into binary data. Finally, the binary data are encoded into the host image to create an overt image. The pixels of the overt image contain eight groups of codes used for reconstructing the covert image. The eight groups of codes are identification codes, row amount codes, covert-image dimension codes, fractal-image amount codes, starting-pixel codes, character amount codes, character codes, and information codes. The overt image and the host image look almost the same for eyes. Furthermore, the covert image can be directly reconstructed from the overt image without using the host image. The most important feature is that the reconstructed covert image is identical to the original covert image, i.e. there is no distortion in the decoding work.     

基于DMD的哈达玛变换成像光谱仪中交错编码像素点的研究

近年来在哈达玛变换成像光谱仪研究领域中最重要的技术革新在于数字微镜器件在这种光谱仪中的应用,但同时也带来了一些相应的技术问题需要克服。详细的描述和分析了由于数字微镜器件在哈达玛变换光谱仪中的应用导致的编码图像上的部分像素点出现的一种交错编码现象;这种特殊的像素点,编码过程不符合哈达玛变换,在光谱复原过程中需要特殊处理。针对这种交错编码像素点,提出了一种标识方法和解码方法。实验中,向光谱仪中导入一束激光并充满整个视场,在编码的激光图像中确定交错编码像素点的位置。然后变换编码模板上哈达玛编码码道的空间位置,采集两组针对目标的编码图像,通过观察编码图像上一个像素点的灰度值组成的列向量中非零常量与零元素的个数,可以分辨它是否是一个交错编码像素点。其中一组编码图像上交错编码像素点光谱曲线可以通过对另一组编码图像上相应位置的像素点进行哈达玛反变换得到。实线结果证明了这一方法的可行性。     

A New Quantum Gray-Scale Image Encoding Scheme

In this paper, a new quantum images encoding scheme is proposed. The proposed scheme mainly consists of four different encoding algorithms. The idea behind of the scheme is a binary key generated randomly for each pixel of the original image. Afterwards, the employed encoding algorithm is selected corresponding to the qubit pair of the generated randomized binary key. The security analysis of the proposed scheme proved its enhancement through both randomization of the generated binary image key and altering the gray-scale value of the image pixels using the qubits of randomized binary key. The simulation of the proposed scheme assures that the final encoded image could not be recognized visually. Moreover, the histogram diagram of encoded image is flatter than the original one. The Shannon entropies of the final encoded images are significantly higher than the original one, which indicates that the attacker can not gain any information about the encoded images.     

Multifactor authentication reinforces optical security

A new optical method to obtain multifactor image encoding and authentication is proposed. The encoded complex-amplitude image function fulfills the general requirements of invisible content, extreme difficulty in copying or counterfeiting, and real-time automatic verification. This optical technique is attractive for high-security purposes that require multifactor reliable authentication. A demonstration using a combination of biometric images and key codes is provided. Retina images, which are very effective for authentication, are used as biometric signals. To the best of our knowledge, this is the first report on combined multiple signal encoding and simultaneous AND authentications for optical security reinforcement.     

On a predictive scheme for colour image quantization

In this paper we proposed an improved colour image quantization scheme based on predictive coding. Since the neighbouring colour pixels are quite similar in most colour images, the similarity among the encoded pixels is exploited. In the proposed scheme the encoded distinct neighbouring colours are collected to form a smaller state-palette. If the closest colour in the state-palette is quite similar to the current encoding colour pixel, the index of the closest colour in the state-palette is recorded. Otherwise, the closest colour in original colour palette for the current encoding colour pixel is searched and the corresponding index is recorded. The experimental results show that the proposed method achieves good image qualities while requiring much lower bit rates for colour image compression.     

A blind image detection method for information hiding with double random-phase encoding

In this paper, a blind image detection method based on a statistical hypothesis test for information hiding with double random-phase encoding (DRPE) is proposed. This method aims to establish a quantitative criterion which is used to judge whether there is secret information embedded in the detected image. The main process can be described as follows: at the beginning, we decompose the detected gray-scale image into 8 bit planes considering it has 256 gray levels, and suppose that a secret image has been hidden in the detected image after it was encrypted by DRPE, thus the lower bit planes of the detected image exhibit strong randomness. Then, we divide the bit plane to be tested into many windows, and establish a statistical variable to measure the relativity between pixels in every window. Finally, judge whether the secret image exists in the detected image by operating the t test on all statistical variables. Numerical simulation shows that the accuracy is quite satisfactory, when we need to distinguish the images carrying secret information from a large amount of images.     

Double-image self-encoding and hiding based on phase-truncated Fourier transforms and phase retrieval

We propose a method to encrypt two covert images into an overt image based on phase-truncated Fourier transforms and phase retrieval. In this method, the two original images are self-encoded in the manner that one of the two images is directly separated into two phase masks (PMs) and used as keys for encryption, and then multiplied by a PM which is generated by using phase retrieval algorithm. At last, the whole encryption process is completed by a Fourier transform operation. In the decryption process, the image without a separation and the two PMs used as keys for encryption are all treated as encoded data. The cryptosystem is asymmetric which means the keys for encryption are different from those for decryption. Numerical simulations are presented to show the viability and good performance of the proposed method.     

半色调编码计算全息图的数字水印方法

提出一种新的基于信息光学的数字水印方法。该方法将水印信息隐藏于半色调编码的计算全息图之中。通过相位复原技术将需隐藏的水印信息编码为相位函数嵌入在复波前中,其振幅定义为宿主图像,通过计算全息记录复波前并对全息图进行半色调编码完成水印信息的嵌入。水印的提取过程只需对含有水印信息的半色调图像进行光学或数字的傅里叶变换即可完成。并给出了算法有效性的理论分析和仿真实验结果。结果证明这种水印技术对于各种数字图像处理操作具有很高的稳健性,且半色调编码图的二值特性使嵌入水印具有很强的抗打印、抗复印、抗扫描的能力。     

Cross-talk free image encryption and watermarking by digital holography and random composition

In previous image watermarking methods an encoded host image and a watermark image are usually directly added, consequently the two images have cross-talk in the decryption step. To eliminate this effect, we propose a novel method based on digital holography, in which all the image pixels of the two sets of holograms resulted from two hidden images are rearranged and integrated into one set of composite holograms with a random scattering matrix (RSM). In decryption the use of this matrix can ensure the exact retrieval of each hologram, and then the perfect reconstruction of each image without cross-talk noise can be achieved. The feasibility of this method and its robustness against occlusion and additional noise are verified by computer simulations with phase-shifting interferometry and double random-phase encoding technique. This approach is suitable for both two- and three-dimensional images, and the additional RSM as a key provides a much higher level of security.     

Analysis and study of the interlaced encoding pixels in Hadamard transform spectral imager based on DMD

The key innovation in Hadamard transform spectral imager (HTSI) introduced recently is the use of digital micro-mirror device (DMD) to encode spectral information. However, because the size of individual micro-mirrors does not match the detector pixel size or for other unavoidable errors in the optical design and the system assembling, an interlaced encoding phenomenon appears on some pixels of the encoded images obtained from the detector. These interlaced encoding pixels are not encoded based on Hadamard transform, so they should be processed specially in spectrum recovery. This paper analyzes the interlaced encoding phenomenon and proposes a positioning method and a decoding method for the interlaced encoding pixels on the encoded images. In our experiment, we direct a beam of laser into our HTSI and fill the entire field of view; by observing the column vector, which is made up of the gray values of a pixel on the encoded images from the detector in sequence, the interlaced encoding pixels can be distinguished easily and a coefficient is obtained simultaneously, which denotes the ratio of the area between the left part and the right part of the interlaced encoding pixel. By substituting the coefficient and the encoded gray values of the interlaced pixel into its encoding equation, we can recover the spectral elements of the interlaced pixel with ease. By comparing the spectral curve of the interlaced encoding pixels recovered by the method mentioned in this paper and the spectral curves of its two adjacent pixels, we find the decoding results are quite effective.     

A least squares quantization table method for direct reconstruction of MR images with non-Cartesian trajectory

The direct Fourier transform method is a straightforward solution with high accuracy for reconstructing magnetic resonance (MR) images from nonuniformly sampled k-space data, given that the optimal density compensation function is selected and the underlying magnetic field is sufficiently uniform. The computation however is very time-consuming, making it impractical especially for large-size images. In this paper, the least squares quantization table (LSQT) method is proposed to accelerate the direct Fourier transform computation, similar to the recently proposed methods such as using look-up table (LUT) or equal-phase-line (EPL). With LSQT, all the image pixels are first classified into several groups where the Lloyd-Max quantization scheme is used to ensure the minimal classification error. The representative value of each group is stored in a small-size LSQT in advance to reduce the computational load. The pixels in the same group receive the same contribution, which is calculated only once for each group instead of for each pixel, resulting in the reduction of computation because the number of groups is far smaller than the number of pixels. Finally, each image pixel is mapped into the nearest group and its representative value is used to reconstruct the image. The experimental results show that the LSQT method requires far smaller memory size than the LUT method and fewer multiplication operations than the LUT and EPL methods. Moreover, the LSQT method can perform large-size reconstructions that achieve comparable or higher accuracy as compared to the EPL and gridding methods when the appropriate parameters are given. The inherent parallel structure also makes the LSQT method easily adaptable to a multiprocessor system.     

利用不确定性提高击中击不中变换的抗畸变能力

对用于目标识别技术的形态学击不中变换进行了分析,引入不确定和模式的概念使得容易受到畸变干扰的像素点对判别结果的作用降低,得到联合排序多值击中击不中变换,从而在不损失图像信息的前提下,提高了目标识别的抗畸变能力,并且具有在输入图像和参考模板之间进行精确匹配的能力。基于非相干相关器,利用新颖的多值互补编码方法,实现了二值图像的联合序多值击中击不中变换,达到了较好的实验结果。     

基于空-谱约束的中餐馆过程混合模型高光谱图像聚类方法

高光谱图像分类是高光谱研究的重要内容,也是许多其他应用的前提。针对传统高光谱图像分类仅考虑光谱信息而忽略空间信息的问题,对距离依赖的中餐馆模型(distance dependent Chinese restaurant process, ddCRP)进行改进,提出一种基于空-谱约束的中餐馆过程混合模型(spatial-spectral Chinese restaurnt process, ssCRP)用于高光谱图像聚类。该模型充分考虑像素邻域的空间和光谱信息,并将其统一纳入模型的建模及求解过程中,得到一般基于像素的聚类方法无法实现的效果,可在一定程度上满足高光谱图像聚类分析的需求。首先,为利用高光谱图像的空间和光谱信息,定义基于像素空间距离和光谱角的指数衰变函数作为像素间相似性的度量。然后,在考虑像素相似性的基础上利用基于餐桌的构造形式为每个像素确定所在的餐桌。最后,对每张餐桌分配一道菜作为聚类类别,从而达到聚类的目的。利用航空可见-近红外成像光谱仪AVIRIS高光谱影像评估该模型性能,实验结果表明：ssCRP模型可较好地实现高光谱图像的自动聚类,与传统的K-means和ISODATA方法相比,该模型结果斑块规整,“椒盐效应”得到抑制,具有较高的空间一致性,分类精度高,其总体精度达到63.57%,Kappa系数为0.632 3,能很好反映真实地物分布。同时,分类结果的地物间边界清晰,能很好保持图像边缘。     

Triple image encryption scheme in fractional Fourier transform domains

We proposed a triple image encryption scheme by use of fractional Fourier transform. In this algorithm, an original image is encoded in amplitude part and other two images are encoded into phase information. The key of encryption algorithm is obtained from the difference between the third image and the output phase of transform. In general case, random phase encoding technology is not required in the proposed algorithm. Moreover, all information of images is preserved in theory when image are decrypted with correct key. The optical implementation of the algorithm is presented with an electro-optical hybrid structure. Numerical simulations have demonstrated the efficiency and the security of this algorithm. Based on this scheme a multiple image algorithm is expanded and designed.     

基于RGB图像传输的双随机相位加密隐藏技术

提出了一种通过彩色宿主图像隐藏双随机相位编码信息的方法.将需隐藏的原始信息,经双随机相位编码,压缩后按一定的编码规则隐藏在宿主图像(RGB图像)的低位.在提取隐藏图像过程中直接对携带隐藏信息的融合图像进行处理,不需要利用原始RGB宿主图像,且重构图像的质量较好,不受原始宿主图像的影响.在此基础上对因原始隐藏信息在编码、存储、传输过程中对融合图象和重构图象的影响做了分析,并在MATLAB环境中对分析结果做了模拟验证.结果表明,该方法可以得到非常好的重构图象.     

Multiple-image hiding based on interference principle

A method for hiding multiple images into one image is presented. The method is based on interference principle and double random phase mask method. A uniform plane wave interferes with two beams of light wave carrying information of two encrypted images on an output plane. The obtained interference distribution image contains information of two encrypted images. By using frequency spectrum center shift technique, the two encrypted images can be recovered successfully. Then, the interference distribution is encoded into an index matrix through a host image. The optical encryption system parameters and the host image can all be used as encryption keys, which make encrypted image information safer. Numerical simulation indicates that the method can encrypt more information into one image and reconstruct the encryption image information successfully.     

基于空间二进制编码的3 D形貌测量方法

介绍了一种基于空间二进制编码的非接触３ Ｄ 形貌测量方法。它用一台ＬＣＤ 投影仪对被测物体表面进行空间编码,再用一台ＣＣＤ 摄像机获取物体编码信息,最后用三角法原理从摄像机图像中获取三维形貌数据。提出了基于三角法的空间二进制码的重要特性,描述了高效编码的构造方法。用这个构造方法构造出一个完全数字化的７ 位字长的二进制编码。基于这种编码的３ Ｄ 形貌测量方法在被测物体表面非常不连续和非构造的环境下取得了良好的测量结果。     

Multifocus image fusion scheme using focused region detection and multiresolution

To solve the fusion problem of the multifocus images of the same scene, a novel algorithm based on focused region detection and multiresolution is proposed. In order to integrate the advantages of spatial domain-based fusion methods and transformed domain-based fusion methods, we use a technique of focused region detection and a new fusion method of multiscale transform (MST) to guide pixel combination. Firstly, the initial fused image is acquired with a novel multiresolution image fusion method. The pixels of the original images, which are similar to the corresponding initial fused image pixels, are considered to be located in the sharply focused regions. By this method, the initial focused regions can be determined, and the techniques of morphological opening and closing are employed for post-processing. Then the pixels within the focused regions in each source image are selected as the pixels of the fused image; meanwhile, the initial fused image pixels which are located at the focused border regions are retained as the pixels of the final fused image. The fused image is then obtained. The experimental results show that the proposed fusion approach is effective and performs better in fusing multi-focus images than some current methods.