Search

Abstract A phase recovery method from a single fringe pattern with closed fringes is developed. The interferogram is first normalized and then rotated to create a new fringe pattern. Both interference images are multiplied which results in the sum of the cosines of the symmetric and asymmetric components of the phase respect to the rotating axis. If the original phase contains tilt and also possesses a high degree of symmetry respect to the rotating axis, the cosine of the asymmetric term will be composed of tilt and a small asymmetric term. In this case, the Fourier transform of the multiplication will be given by two high intensity peaks localized symmetrically respect to the origin and a broader lobule centered at the origin. The asymmetric component of the phase is then recovered with a Fourier method and used to calculate the phase of the original interferogram. The above procedure may serve as an alternative to other methods that works iteratively to recover the phase from a single interferogram with closed fringes as it is demonstrated in experimental and simulated data. [ABSTRACT FROM AUTHOR]

Abstract Optical imaging systems with extended depth of field based on wavefront coding can be used in many fields, which require more object information along the optical axis in a snapshot. When using the non-rotational symmetric phase masks such as cubic phase mask, the final images are usually restored by classical wiener restoration method. However, the existence of image artifacts in final restored images is a problem to be solved. We proposed a method to alleviate the image artifacts by processing two conjugate images, which are captured by image sensor before and after rotating the phase mask 180 degrees along the optical axis. Unlike the previous methods usually need to measure the point spread function or optical transfer function of the imaging system, we do not need to measure them anymore. Both the ZEMAX simulation and experiment verified our method. [ABSTRACT FROM AUTHOR]

This paper proposes a Hash based authentication scheme that employs equal modulus decomposition (EMD) and fractional joint transform correlator. An 8-bit grey scale image is separated into its constituent bit plane matrices. Each bit plane matrix is subjected to EMD encryption procedure employing numerically generated random phase mask (RPM) and amplitude mask (AM). The EMD encryption results into two complex functions, which are used for the generation of phase mask and amplitude mask for the next bit plane matrix. A two round EMD procedure is carried out to obtain an 8-bit intensity matrix which is Fourier transformed and its central frequency components are extracted to obtain a 256-bit Hash value. Numerical simulations have been carried out to validate the effectiveness and performance of the proposed scheme. [ABSTRACT FROM AUTHOR]

In this paper, we propose a simple, novel method to suppress background noise in confocal scanning fluorescence microscopy images with superoscillations. The proposed method retains high resolution, while completely removing superoscillation sidebands. Simulations of images from conventional confocal scanning microscopy, superoscillations, and the proposed method are presented, demonstrating its effectiveness. [ABSTRACT FROM AUTHOR]

We propose a method of topological charge number multiplexing based on the JTC encryption system to achieve multiple-image encryption. Using this method, multi-image can be encrypted into single ciphertext, and the original images can be recovered according to the authority level. The number of encrypted images is increased, moreover, the quality of decrypted images is improved. Results of computer simulation and initial experiment identify the validity of our proposed method. [ABSTRACT FROM AUTHOR]

An image multiplexing and authentication method based on the double-phase retrieval algorithm (DPRA) with the manipulations of wavelength and position in the Fresnel transform (FrT) domain is proposed in this study. The DPRA generates two matched phase-only functions (POFs) in the different planes so that the corresponding image can be reconstructed at the output plane. Given a number of target images, all the sets of matched POFs are used to generate the phase-locked system through the phase modulation and synthesis to achieve the multiplexing purpose. To reconstruct a target image, the corresponding phase key and all the correct parameters in the FrT are required. Therefore, the authentication system with high-level security can be achieved. The computer simulation verifies the validity of the proposed method and also shows good resistance to the crosstalk among the reconstructed images. [ABSTRACT FROM AUTHOR]

In optical encryption systems, speckle noise is one major challenge in obtaining high quality decrypted images. This problem can be addressed by employing a QR code based noise-free scheme. Previous works have been conducted for optically encrypting a few characters or a short expression employing QR codes. This paper proposes a practical scheme for optically encrypting and decrypting a gray-scale image based on QR codes for the first time. The proposed scheme is compatible with common QR code generators and readers. Numerical simulation results reveal the proposed method can encrypt and decrypt an input image correctly. [ABSTRACT FROM AUTHOR]

Fresnel diffraction of curved grating with the parabolic cylinder, the cylindrical surface or the elliptic cylinder profile, is studied theoretically and experimentally. The transmittance function of grating with the smaller curvature is expressed by Fourier series and the mathematic expression of the diffraction intensity in Fresnel region is deduced. The influence of the curvature of grating on the diffraction distribution is analysed theoretically. The simulation results show the longitudinal intensity distribution of curved grating takes on the divergence structure, and this structure gets clearer with increase of the curvature degree. The transverse distribution at Talbot distance deviates from the grating structure and the magnified image of grating appears at modified Talbot distance. One practical experiment is conducted and the experimental results verify these theoretic predictions. The work of this paper will be helpful for understanding the diffraction of curved grating and prompting the application of Talbot effect of grating in wave-front sense and optical encode. [ABSTRACT FROM AUTHOR]

We demonstrate an optical image encryption scheme using 3-D chaotic map based joint image scrambling and random encoding in gyrator domains. A novel image confusion approach that can well address the drawbacks of typical image permutation ciphers is developed to firstly shuffle the plaintext. Then the scrambled image is random phase encoded in the spatial domain and gyrator transform domain. A three-dimensional chaotic map is introduced to generate key stream elements. Simulations demonstrate that the cryptosystem has satisfactory cryptographic features and owns high robustness against noise perturbation as well as occlusion attack. [ABSTRACT FROM AUTHOR]

A set of active partially pixelated masks is designed to pick up appropriate images from a large number serial pictures or a three-dimensional computer numerical model for the natural three-dimensional display with smooth motion parallax. To realize the smooth three-dimensional display without view zone jumping, each subpixel at the boundary in the pixelated mask is subdivided into partial pixels. Each active partially pixelated mask can periodically shift according to the design requirement. With active partially pixelated masks in the liquid crystal panel combining with a precision lenticular lens array, the three-dimensional display with 500 views from captured serial pictures and 1200 views from a computer numerical model is demonstrated in 56° viewing angle, which is functionally equivalent to the holographic stereogram. The displayed depth is more than 40cm. The light intensity ripple with 18 active partially pixelated masks is decreased to 0.9% in the viewing zone. The screen size is 50.7cm×28.5cm. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we show that amplitude- and phase-truncation-based optical asymmetric cryptosystem is vulnerable to known-plaintext attack. The decryption keys are generated with the help of modified Gerchberg–Saxton phase retrieval algorithm from known-plaintext and ciphertext. With the help of the generated keys, the encrypted image, which is encrypted using encryption keys placed in either of the domains (Fourier, Fresnel, or fractional Fourier domain) is decrypted successfully. The vulnerability is proved through the results of computer simulation. [Copyright &y& Elsevier]

Abstract: An optical authentication technique based on interference image hiding system and phase-only correlation is proposed. In this method, some predefined complex images with different amplitudes and the same phase are respectively encoded into two phase-only masks according to the interference principle. This technique can easily generate different verification keys for different users, so it brings convenience for multi-user application. In the verification stage, both a sharp correlation peak and a significant image represented the identity of a user are generated simultaneously. Therefore, in addition to simple verification, this method can also recognize the identity of the user. Moreover, this technique can effectively avoid the verification key being forged by other person. All the performances and the feasibility of our proposed method are tested by numerical simulations. [Copyright &y& Elsevier]

Abstract: In recent years, a number of methods have been proposed in the literature for the encryption of two-dimensional information by using the fractional Fourier transform, but most of their encryptions are complex values and need digital hologram technique to record information, which is inconvenient for digital transmission. In this paper, we propose a new approach for image encryption based on the real-valuedness and decorrelation property of the reality-preserving multiple-parameter fractional Fourier transform in order to meet the requirements of the secure image transmission. In the proposed scheme, the original and encrypted images are respectively in the spatial domain and the reality-preserving multiple-parameter fractional Fourier transformed domain determined by the encryption keys. Numerical simulations are performed to demonstrate that the proposed method is reliable and more robust to blind decryption than several existing methods. [Copyright &y& Elsevier]

Abstract: The original hierarchical watermarking scheme for image tamper detection and recovery has simple computation and high performance precision which can achieve 2×2 subblock. However, four-scanning and blind attacks have been proposed recently on this scheme. We generalize these attacks and analyze the cause of security flaws. We think that it is promising to improve the original scheme''s security and keep its merit at the same time. In order to defeat these attacks, we develop an improved method to generate a block mapping sequence by sorting the chaotic sequence and add the chaotic encryption and permutation based on the exact content of each subblock to be the post-processing of the 3-tuple watermark. Our method uses the simple watermarking scheme and satisfies the performance requirements of fragile watermarking, such as high-precision tamper detection, localization and recovery. Theoretical analysis and computer simulation demonstrate that our proposed scheme is much more secure and can overcome possible attacks. [Copyright &y& Elsevier]

Abstract: A new double-image encryption method on the joint transform correlator using two-step-only quadrature phase-shifting digital holography, based on the calculated intensity of reference beam is proposed. The technique realizes the double-image encryption using one random phase encoding on the joint transform correlator; and only records two quadrature-phase holograms on CCD camera without recording reference-wave intensity or object-wave intensity. With the acquired reference-wave intensity from 2-D correlation coefficient and the keys known, the clear retrieved image can be obtained at high speed by certain algorithm. Its feasibility and validity were verified by a series of computer simulations. [Copyright &y& Elsevier]

Abstract: A novel double image encryption method is proposed by utilizing double pixel scrambling technique and random fractional Fourier domain encoding. One of the two original images is encoded into the phase of a complex signal after being scrambled by one matrix, and the other original image encoded into its amplitude after being scrambled by another matrix. The complex signal is then encrypted into stationary white noise by utilizing double random phase encoding in fractional Fourier domain. By applying the correct keys with fractional orders, the random phase masks and the pixel scrambling operation, the two original images can be retrieved without cross-talk. Numerical simulations have been done to prove the validity and the security of the proposed encryption method. [Copyright &y& Elsevier]

Abstract: A new method for image encryption based on optical coherent superposition and basic vector operations is proposed in this paper. In this encryption, the original image can be directly separated into two phase masks (PMs). One is a random phase mask (RPM) and the other is a modulation of the RPM by the original image. The mathematical calculation for obtaining the two PMs is quite simple and direct resulting from the simple principle of optical coherent superposition. The arbitrarily selected RPM can be treated as the encrypted result while the PM can be taken as the key for decryption. With this technique, the same encrypted result can be obtained for different images with the same size while the keys for decryption are different. The encryption can be performed digitally and the decryption can be performed optically or digitally. The security of the proposed method is discussed and computer simulation results are presented to verify the validity of proposed method. [ABSTRACT FROM AUTHOR]

Abstract: A wavefront reconstruction method by two-step generalized phase-shifting interferometry (GPSI) with blind phase shift extraction algorithm is verified by both the computer simulations and optical experiments. This method can retrieve complex object wave field by using two interferograms, the recorded object and reference wave intensities, and an unknown phase shift without additional processing. The simulations with irregular wavefronts have shown the effectiveness and high accuracy of this method for blind phase-shift extraction and wavefront reconstruction over a wide range of phase-shifts, while the optical experiments for both the direct and indirect objects have yielded satisfactory results with a higher resolution of reconstructed image than those reported recently. [Copyright &y& Elsevier]

Abstract: Our analysis reveals that the complex wave error caused by arbitrary phase-shift errors in generalized phase-shifting interferometry (PSI) with arbitrary frames and arbitrary phase shift design takes the common form: a linear combination of the correct complex wave and its conjugation. Consequently, the simple method of digital wave correction we proposed recently for standard PSI is extended to the generalized PSI of any algorithms. Computer simulations show that this method can depress both the amplitude error and the phase error simultaneously and significantly by 2–3 orders of magnitude for arbitrary irregular phase shift errors as large as up to 20% without the need of calibration or the knowledge of the actual phase shifts. [Copyright &y& Elsevier]