Showing papers by "Xiang Peng published in 2017"

Ciphertext-only attack on optical cryptosystem with spatially incoherent illumination: from the view of imaging through scattering medium.

Abstract: Security analysis is important and necessary for a new cryptosystem. In this paper, we evaluate the security risk of the optical cryptosystem with spatially incoherent illumination from the view of imaging through scattering medium and then demonstrate that it is vulnerable to ciphertext-only attack. The proposed ciphertext-only attack method relies on the optical memory effect for speckle correlations, which reveals a fact that the ciphertext's autocorrelation is essentially identical to the plaintext's own autocorrelation. Furthermore, by employing of an improved dynamic hybrid input-output phase-retrieval algorithm, we show that a plaintext image can be directly reconstructed from the autocorrelation of its corresponding ciphertext without any prior knowledge about the plaintext or the phase keys. Meanwhile, the theory analysis and experiment results will also be provided to verify the validity and feasibility of our proposed ciphertext-only attack method. To the best of our knowledge, this is the first time to report optical cryptanalysis from the point of view of imaging through scattering medium and we believe this contribution will open up an avenue to deepen the investigation of optical cryptosystems.

Phase-3D mapping method developed from back-projection stereovision model for fringe projection profilometry.

Abstract: Two major methods for 3D reconstruction in fringe projection profilometry, phase-height mapping and stereovision, have their respective problems: the former has low-flexibility in practical application due to system restrictions and the latter requires time-consuming homogenous points searching. Given these limitations, we propose a phase-3D mapping method developed from back-projection stereovision model to achieve flexible and high-efficient 3D reconstruction for fringe projection profilometry. We showed that all dimensional coordinates (X, Y, and Z), but not just the height coordinate (Z), of a measured point can be mapped from phase through corresponding rational functions directly and independently. To determine the phase-3D mapping coefficients, we designed a flexible two-step calibration strategy. The first step, ray reprojection calibration, is to determine the stereovision system parameters; the second step, sampling-mapping calibration, is to fit the mapping coefficients using the calibrated stereovision system parameters. Experimental results demonstrated that the proposed method was suitable for flexible and high-efficient 3D reconstruction that eliminates practical restrictions and dispenses with the time-consuming homogenous point searching.

Simple and flexible phase compensation for digital holographic microscopy with electrically tunable lens.

Abstract: In a digital holographic microscopy (DHM) system, different microscope objectives (MOs) will introduce different phase distortions and thus lead to measurement errors. To address this problem, we present a simple and flexible method to compensate all phase distortions by introducing an electrically tunable lens (ETL) in the reference arm for a DHM system with multiple MOs. By exactly controlling the external currents of the ETL, we can change the reference wave front to match the wave front introduced by different MOs without complex alignment or additional numerical postprocessing manipulations. This method is suitable for quantitative real-time phase imaging especially when it refers to multiple MOs. To demonstrate the validity and effectiveness of our scheme, we did a series of simulations and carried out some real experiments with two different MOs (4× and 10×).

Improved performance of multi-view fringe projection 3D microscopy.

Abstract: Fringe projection 3D microcopy (FP-3DM) plays an increasingly important role in micro manufacturing and measurement. In recent decades, research on FP-3DM has made considerable progress. Nevertheless, some disadvantages arising from the limited depth of field, local specular reflection and occlusion still exist and need to be further addressed. In this paper, a multi-view FP-3DM (MVFP-3DM) is presented. Four imaging branches with the Scheimpflug condition and one vertical projection branch are deployed to establish the system. The system is described with a general imaging model, which is independent of the system configuration. In system calibration, the edge of binary fringe is used to locate the benchmark, which takes advantage of the fact that the edge will keep its position whether it is in focus or out of focus. Furthermore, a group of experiments prove that our proposed MVFP-3DM system can extend measurable range in depth, improve precision in 3D reconstruction and reduce occlusion.

Off-axis tilt compensation in common-path digital holographic microscopy based on hologram rotation.

Abstract: We present a simple and effective compensation method for the off-axis tilt in common-path digital holographic microscopy (CPDHM) by introducing a rotating operation on the hologram. The proposed method mainly requires a digital reference hologram (DRH), which is a rotated version of the original one; it is assumed to be easy to obtain by rotating the specimen's hologram 180°. In this way, the off-axis tilt could be removed by subtracting the retrieved phase of DRH from the retrieved phase of the original hologram, but without any complex spectrum centering judgment, fitting procedures, or prior knowledge of the system. This highly automatic and efficient performance makes our approach available for real-time quantitative phase imaging (QPI), although it limits the field of view (FOV) of the specimen. Some experimental results of microlens array and phase plate demonstrate the feasibility and effectiveness of the proposed method.

Automatic and rapid whole-body 3D shape measurement based on multinode 3D sensing and speckle projection

Abstract: Automatic and rapid whole-body 3D shape measurement has attracted extensive attention in recent years and been widely used in many fields. Rapid 3D reconstruction, automatic 3D registration, and dedicated system layout are critical factors to enable an excellent 3D measurement system. In this paper, we present an automatic and rapid whole- body 3D measurement system that is based on multinode 3D sensors using speckle projection. A rapid algorithm for searching homologous point pairs is suggested, which takes advantage of the optimized projective rectification and simplified subpixel matching techniques, leading to an improved time efficiency of 3D reconstruction. Meanwhile, a low-cost automatic system with a flexible setup and an improved calibration strategy are proposed, where system parameters of each node sensor can be simultaneously estimated with the assistance of a cubic and a planar target. Furthermore, an automatic range data registration strategy by employing two aided cameras is investigated. Experiment results show that the presented approach can realize automatic whole-body 3D shape measurement with high efficiency and accuracy.

Optical Cryptanalysis Method Using Wavefront Shaping

Abstract: Optical techniques for information security have drawn a lot of attention in recent years. The development of cryptanalysis strategies will also have a positive promotion for the cryptosystems themselves. However, most of the present publications on cryptanalysis of optical cryptosystems are focusing only on theoretical analysis but not on experimental verification. In this paper, a practical optical cryptanalysis method using wavefront shaping is proposed. Considering that the confusion and diffusion of information in the optical cryptosystem are actually caused by scattering effect of random phase mask(s), the proposed method employs a point source function and the feedback-based optimization algorithm, which can obtain an equivalent key of the optical cryptosystem. In such a way, the confusion and diffusion of the random phase mask(s) in the cryptosystem could be removed successfully. To the best of our knowledge, this is the first time the attack strategy from the perspective of wavefront shaping can be seen, and one of the biggest advantages is that it could get an equivalent key of the cryptosystem without deducing its original keys.

Double-image optical encryption method with high safety intensity and decryption method thereof

Abstract: The present invention relates to a double-image optical encryption method. The method comprises: two images P1(x, y) and P2(x, y) to be encrypted are respectively taken as an amplitude and a phase to combine a complex amplitude plaintext P(x, y) which clings to a random phase template M0(x, y) and is arranged at the input plane of an optical 4f system; a plane wave generated by a beam of the coherent light is employed to vertically irradiate the input plane of the system, three different random phase templates M1(u, v), M2(u, v) and M3(u, v) are respectively arranged at a frequency spectrum surface at three exposures for applying different frequency domain phase modulation, and the three corresponding intensity graphs I1(x, y), I2(x, y) and I3(x, y) are recorded on an output plane to be taken as the system cryptographs. The present invention further provides a decryption method corresponding to the double-image optical encryption method. The method comprises: providing the initial conjecture of the complex amplitude plaintext; and employing the corrected GS iteration phase retrieval algorithm to perform iteration processing with preset times of the initial conjecture to obtain the plaintext so as to extract two secret images. The double-image optical encryption method with high safety intensity and the decryption method thereof can greatly improve the safety of the encryption method.

Multi-level key generating method based on dual-beam interference and user hierarchical authentication method

Abstract: The invention relates to a multi-level key generating method based on dual-beam interference and a hierarchical authentication method. The generating method comprises the following steps: saving at least two standard reference images; selecting a random pure phase distribution function to serve as a phase lock; coding each of the at least two standard reference images into a sparse phase distribution corresponding to an input plane by an iterative phase recovery processing process; and overlaying the at least two obtained sparse phase distributions according to different quantities to obtain phase keys of different authentication levels. The hierarchical authentication method comprises the following steps: acquiring interference field strength distributions of the phase lock and the phase keys on an output plane; calculating an interference field strength distribution and non-linear correlation distributions of the at least two standard reference images by a non-linear correlation algorithm; and taking the quantity of the standard reference images in which remarkable nonlinear correlation peaks relative to the interference field strength distribution appear as the authorization levels of the phase keys.

Portable 3D scanning system based on an inertial sensor

Abstract: Portable 3D scanning systems are increasingly used in many applications at present as a result of its high flexibility, portability and high efficiency. Iterative closest points method is widely used for multi-view measurement results registration. However, there are many restrictions for portable system, the alignment often depends on landmarks on object surface or object features, in some applications, it may not achieve satisfactory expectations. In this paper, we propose to conduct the registration based on pose estimation from a low cost inertial sensor, which will increase the measurement effectiveness. Test result demonstrates that the method is feasible. With attitude information inside the system, the measurement device does not need external support information and has good prospects for application.

Method and apparatus for obtaining equivalent key of random phase coding-based optical encryption system

Abstract: The present invention relates to a method and apparatus for obtaining the equivalent key of the random phase coding-based optical encryption system. The apparatus includes a point light source structure, an optical 4f structure, a pure phase space light modulator and a feedback control device. According to the apparatus, the phase modulation parameter of the pure phase space light modulator is adjusted, so that the light intensity of the center of an output surface image can be maximum, and the phase modulation parameter is adopted as the equivalent key of the optical encryption system. According to the method, modulation is completed through the apparatus. With the method and apparatus adopted, the equivalent key of the optical encryption system parameter can be obtained simply, and cost is low.

Speckle-correlation-based ciphertext-only attack on the double random phase encoding scheme

Abstract: The speckle correlation technique is applied to ciphertext-only attack (COA) on optical cryptosystem based on double random phase encoding. According to the inherent merits of speckle correlation, we have revealed a fact that the ciphertext’s autocorrelation is essentially identical to the plaintext’s own autocorrelation. Then, a plaintext image can be directly reconstructed from the autocorrelation of its corresponding ciphertext by employing a iterate phase-retrieval algorithm. This could then lead to a potential security flaw because an unauthorized user could directly retrieve the plaintext from an intercepted ciphertext by performing proposed COA approach. Meanwhile, a series of numerical simulations will also be provided to verify the validity and feasibility of our proposed COA method.

Sub secret key generation method and decryption or authentication method for optical threshold coding

Abstract: The invention relates to a sub secret key generation method and decryption or authentication method for optical threshold coding. The generation method that is used for generating three sub secret keys in pure phase distribution for plaintext image information or authentication image information and using any two sub secret keys for recovering the plaintext image information or realizing successful authentication comprises: plaintext information or authentication image information is coded by using a phase retrieval algorithm to an initial first sub secret key, second sub secret key, and third sub secret key; and phase updating is carried out on the initial first sub secret key, second sub secret key, and third sub secret key by using a sub secret key authentication image for verifying sub secret key legality, thereby obtaining a final first sub secret key, second sub secret key, and third sub secret key that include the sub secret key authentication image information. Therefore, sub secret key counterfeiting can be prevented. The methods can be realized by using the simple optical system, so that realization becomes simple.

Comparison of active, passive and adaptive phase error compensation methods using a universal phase error model

Abstract: Nonlinear intensity response, namely gamma effect, of the projector-camera setup introduces phase error in phase-shifting profilometry. This paper presents a comparison of three phase error compensation methods: active, passive and adaptive, using a universal phase error model. The active method calibrates a gamma factor to modify the projected fringe patterns; the passive method implement an iterative procedure to work out an optimal phase map; the adaptive method compensate phase error based on Hilbert transform without any auxiliary conditions. Comparison Experiments were implemented in three and four phase-shifting steps, which demonstrated that the active method provided an excellent performance regardless the phase-shifting step, yet the passive method might fail when the phase error was large; the adaptive method could be in the same level as the passive method in four phase-shifting step.

3D Models to Educated Museum Interactive Exhibition with Computing Techniques

Abstract: The use of 3D scanner for the digitalization of 3D objects of cultural heritage is now an established approach. This paper aims at contributing to a better understanding of the emergence of new ideas in exhibition and education with such an approach. Researcher takes advantage of 3D optical technology cooperate with digital museum exhibition, the procedure of 3D scanning has been demonstrated in this research paper. Then, we create a mobile application which concentrate interactive design, computer technique in image tracking algorithm, and virtual model with 3D optical technology. The aim of research in virtual museum opens up a new area for the museum education and interaction. The results we obtain allow us to devise methods for enhancing creativity.

Phase error compensation method and apparatus

Abstract: A phase error compensation method and apparatus. The method comprises: acquiring a stripe sequence diagram via a phase-shifting profilometry measuring system (S101); transforming the stripe sequence diagram from a spatial domain into a Hilbert transform domain based on Hilbert transform (S102); respectively solving phases for the stripe sequence diagrams of the spatial domain and the Hilbert transform domain based on a least square phase-shifting method, and obtaining a spatial domain phase diagram and a Hilbert transform domain phase diagram (S103); and averaging the spatial domain phase diagram and the Hilbert transform domain phase diagram, obtaining an average phase, and performing phase error compensation by utilizing the average phase (S104). The present invention has a self-compensation mechanism, does not need additional supplementary conditions, and satisfies high-speed, high-precision and high-universality three-dimensional digital imaging and measuring requirements based on phase-shifting profilometry.

Selection of F/number in lattice design for stitching inferferometry of aspheric surface

Abstract: Subaperture stitching interferometry has been proven to be a promising method for precision metrology of aspheric surfaces. However, due to the aspheric departure, selection of F/number of the transmission sphere for aspheres is more complicated than spheres or flats. This paper proposed an optimization method to determine the maximum subaperture width based on the slope resolution of the standard interferometer. With it, the transmission sphere is selected with an optimal F/number. On the basis of the transmission sphere and overlap rate, we not only can ensure the fringes of off-axis subapertures are resolvable by the interferometer, but also can minimize the number of subapertures required to cover the full aperture of the surface. Finally, some numerical examples are given to illustrate the procedure, and also to verify the validity of our proposed method.