A multiple-image cryptographic authentication scheme based on phase-only holograms is proposed in this paper. First, computer-generated holograms of original images to be authenticated are encoded to phase-only holograms using the Floyd-Steinberg error diffusion algorithm. Second, each phase-only hologram image is randomly sampled as the sparse representation with the help of its random binary mask. Finally, the phase-only ciphertext containing the information of original images is obtained by integrating all sparse representations using their binary masks. The existence of each original image can be verified by calculating the nonlinear correlation map between it and its corresponding decrypted result. High security level of this cryptosystem can be achieved by considering random binary masks as secret keys. This work provides an effective alternative for the related research based on computer-generated holograms.
An optical image encryption method is proposed based on Fourier single-pixel imaging and iterated phase retrieval algorithm. First, a binary barcode image containing two groups of horizontal strips is randomly generated and used as the target image in the single-pixel imaging process. Second, considering the barcode image as the amplitude constraint, the original plaintext image is encoded to two phase-only masks using a designed phase retrieval algorithm in Fresnel domain, and these masks are applied as secret keys. Finally, the barcode image is encrypted to a series of measurements using two-step phase shift Fourier single-pixel imaging as the ciphertext. Differing other methods, the original image is not directly imaged and encoded into the ciphertext. Even the ciphertext is obtained by a cracker, only the barcode image may be further discovered. Due to two phase-only masks as secret keys, the security level of the cryptosystem can be enhanced greatly. The simulated results verify the feasibility of the proposed method, and this work provides an effective alternative for the related research.
With the development of privacy protection, reversible data hiding methods in encrypted image have drawn extensive research interest. Among them, a new method is proposed based on embedding prediction errors, i.e., EPE-based method, where secret information is embedded in the encrypted most significant bit plane. Not only the original image can be recovered with high quality but also the payload can reach close to 1 bit per pixel (bpp). However, there are potential errors in the process of extracting secret data, because most significant bits of a part of pixels are used as flags to mark prediction error location. In this paper, a reversible data hiding method in encrypted image with high capacity is proposed by combining most significant bit prediction with least significant bit compression. At first, most significant bit of each pixel is predicted and a location map of prediction errors in the original image is generated. In the same time, the original image is encrypted using a stream cipher method. Then, the location map is embedded into the vacated space generated with compressing least significant bits and the secret data is embedded into most significant bits of a part of pixels without prediction errors. In this way, the marked encrypted image is obtained. Finally, the original image can be recovered without any error and the secret information can be extracted correctly from the marked encrypted image. Experimental results show that the proposed method has better performance than EPE-based and other methods.
A single-channel color image encryption method is proposed based on iterative phase iterative process in quaternion Fourier transform domain. First, three components of the plain color image is confused respectively by using cat map. Second, the confused components are combined into a pure quaternion image, which is encode to the phase only function by using an iterative phase retrieval process. Finally, the phase only function is encrypted into the gray scale ciphertext with stationary white noise distribution based on the chaotic diffusion, which has camouflage property to some extent. The corresponding plain color image can be recovered from the ciphertext only with correct keys in the decryption process. Simulation results verify the feasibility and effectiveness of the proposed method.
A double-image encryption scheme is proposed based on an asymmetric technique, in which the encryption and decryption processes are different and the encryption keys are not identical to the decryption ones. First, a phase-only function (POF) of each plain image is retrieved by using an iterative process and then encoded into an interim matrix. Two interim matrices are directly modulated into a complex image by using the convolution operation in the fractional Fourier transform (FrFT) domain. Second, the complex image is encrypted into the gray scale ciphertext with stationary white-noise distribution by using the FrFT. In the encryption process, three random phase functions are used as encryption keys to retrieve the POFs of plain images. Simultaneously, two decryption keys are generated in the encryption process, which make the optical implementation of the decryption process convenient and efficient. The proposed encryption scheme has high robustness to various attacks, such as brute-force attack, known plaintext attack, cipher-only attack, and specific attack. Numerical simulations demonstrate the validity and security of the proposed method.
MEMS are tiny mechanical devices that are built onto semiconductor chips and are measured in micrometers and
nanometers. Testing of MEMS device is an important part in carrying out their functional assessment and reliability
analysis. Development of systems based on digital holography (DH) for MEMS inspection and characterization is
presented in this paper. Two DH reflection systems, table-top and handheld types, are developed depending on the
MEMS measurement requirements and their capabilities are presented. The methodologies for the systems are
developed for 3D profile inspection and static & dynamic measurements, which is further integrated with in-house
developed software that provides the measurement results in near real time. The applications of the developed systems
are demonstrated for different MEMS devices for 3D profile inspection, static deformation/deflection measurements and
vibration analysis. The developed systems are well suitable for the testing of MEMS and Microsystems samples, with
full-field, static & dynamic inspection as well as to monitor micro-fabrication process.
Camera calibration is the most important step for stereovision measuring system, which affects the accuracy and stability of the measuring system directly. In order to compute the intrinsic and extrinsic parameters of camera, at least seven feature points should be extracted from the calibration board, and the world coordinates of these points should be consistent with their camera coordinates. In this paper, a special planar board utilizing the circular blobs of different sizes is used, and the correspondence between world and image coordinates of these feature points could be built
automatically. Based on an existing algorithm that is used for single camera calibration, the intrinsic and lens radial
distortion parameters can be computed with several image pairs of the planar board that are captured by two cameras in
different orientations as well as the initial orientation and location of cameras. In order to improve the accuracy of object
reconstruction, the bundle adjustment algorithm is further used to optimize the orientation and location of camera.
Experiment results demonstrate the efficiency of proposed method.
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