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    Wyświetlanie 1-9 z 9
    Tytuł:
    Image encryption algorithm based on rear-mounted phase mask and random decomposition
    Autorzy:
    Yadav, Shivani
    Singh, Hukum
    Powiązania:
    https://bibliotekanauki.pl/articles/2086758.pdf
    Data publikacji:
    2022
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    fractional Fourier transform
    random decomposition
    rear-mounted phase mask
    SVD
    singular value decomposition
    Opis:
    To escalate the image encryption a new method has been devised which includes double random phase encoding (DRPE) using rear phase masking and random decomposition (RD) technique stranded on fractional Fourier transform. Here, asymmetric cryptographic system is developed in fractional Fourier transform (FrFT) mode using two random phase masks (RPM) and a rear mounted phase mask. In the projected scheme a colored image is decomposed into R, G and B channels. The amplitude of each channel is normalized, phase encoded and modulated using RPM. The modulated R, G and B channels of the colored image are individually transformed using FrFT to produce corresponding encrypted image. The proposed scheme is authorized on grayscale image also. The norm behind the development of the suggested scheme has been elaborated by carrying out cryptanalysis on system based on the RD. The method helps in escalations of the protection of double random phase encoding by cumulating the key length and the parameter amount, so that it vigorously can be used against various attacks. The forte of the suggested cryptographic system was verified using simulations with MATLAB 7.9.0 (R2008a). The efficiency of the suggested scheme includes the analysis using singular value decomposition (SVD), histogram and correlation coefficient.
    Źródło:
    Optica Applicata; 2022, 52, 2; 195--212
    0078-5466
    1899-7015
    Pojawia się w:
    Optica Applicata
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Experimental study of an anomalous hollow beam with orbital angular momentum
    Autorzy:
    Lu, Xingyuan
    Zhao, Chengliang
    Hoenders, Bernhard J.
    Yang, Yuanjie
    Cai, Yangjian
    Powiązania:
    https://bibliotekanauki.pl/articles/173518.pdf
    Data publikacji:
    2019
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    anomalous hollow beam
    orbital angular momentum
    focused intensity
    Fourier transform
    Opis:
    Anomalous hollow beam has potential applications in the optical trapping and free space optical communications, etc. It is noted that, thus far, although a large number of studies have been carried out in this field, most of them are theoretical studies and only quite a few cases have experimental results. Here, we experimentally study the generating of anomalous hollow beam carrying orbital angular momentum, and measure its topological charge. We show that the number of dark rings in the Fourier transform of intensity patterns is equal to the topological charge. The experimental results agree well with the simulations.
    Źródło:
    Optica Applicata; 2019, 49, 2; 217-226
    0078-5466
    1899-7015
    Pojawia się w:
    Optica Applicata
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Deflectometry for phase retrieval using a composite fringe
    Autorzy:
    Liu, T.
    Zhou, C.
    Liu, Y
    Si, S
    Lei, Z.
    Powiązania:
    https://bibliotekanauki.pl/articles/173892.pdf
    Data publikacji:
    2014
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    wavefront measurement
    fringe analysis
    phase retrieval
    fast Fourier transform (FFT)
    multifrequency heterodyne principle
    Opis:
    An improved deflectometry for wavefront measurement using a composite fringe is proposed to reduce the projection fringes and improve the accuracy. The single composite fringe contains four fringes in different directions. It goes through the tested objects and then is captured by a CCD camera. Two high frequency orthogonal fringe patterns and two single period orthogonal fringe patterns can be obtained from the composite fringe by fast Fourier transform. The unwrapping of the wrapped phase of the high frequency fringe is accomplished by the corresponding single period fringe using a heterodyne method. The wavefront is reconstructed by the integration of partial derivatives. Using only one fringe, the proposed method is more applicable to dynamic wavefront measurement. The experimental results demonstrate that the proposed method can retrieve the complex wavefronts more accurately.
    Źródło:
    Optica Applicata; 2014, 44, 3; 451-461
    0078-5466
    1899-7015
    Pojawia się w:
    Optica Applicata
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    High-security image encryption by multiplexing phase encoding in domains of dual optical transforms
    Autorzy:
    Li, Zhihui
    Gao, Bin
    Pan, Xiaoou
    Li, Linlin
    Wang, Chenxuan
    Zuo, Weizhuo
    Ji, Yu
    Liu, Shutian
    Liu, Zhengjun
    Powiązania:
    https://bibliotekanauki.pl/articles/27310099.pdf
    Data publikacji:
    2023
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    extended fractional Fourier transform
    geometric operations
    random phase encoding
    Opis:
    A novel optical image encryption is proposed based on multiplexing of the random phase encoding with shift and rotation operations in domains of two transforms, extended fractional Fourier transform (eFrFT) and Fresnel transform. The original image is subjected to eFrFT with the action of the random phase mask. The mask is shifted and rotated to enhance the security of this encryption method. The image obtained from eFrFT is entered into Fresnel diffraction by the use of the phase mask to obtain the final encrypted image. We plan for the phase keys to be multiplexed in order to decrease the amount of keys that need to be stored in an application. Here, the displacement, rotation angle, and wavelength in this system can be used as additional keys to improve the security and reliability of the encryption system. Numerical experiments are conducted to verify the effectiveness and security of the method. The findings demonstrate that the keys are sufficiently sensitive for high security.
    Źródło:
    Optica Applicata; 2023, 53, 3; 447--466
    0078-5466
    1899-7015
    Pojawia się w:
    Optica Applicata
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Spectral analysis for tilted fiber Bragg gratings in the corrosion detection for concrete structure
    Autorzy:
    Kwong, Kok Zee
    Udos, Waldo
    Lim, Kok-Sing
    Lee, Foo Wei
    Tan, Chee Ghuan
    Samion, Muhamad Zharif
    Ahmad, Harith
    Powiązania:
    https://bibliotekanauki.pl/articles/2172827.pdf
    Data publikacji:
    2022
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    tilted fibre Bragg grating
    optical spectral analysis
    Fourier transform
    corrosion
    steel bar
    Opis:
    An effective corrosion monitoring technique is sought after by the engineers for assessing the steel bar corrosion at the early stage for the maintenance and repair works, especially in the corrosive environments, such as coastal and marine. In this work, tilted fiber Bragg grating (TFBG) with the optical sensor is employed in corrosion monitoring of a reinforced concrete structure. Taking advantage of the high sensitivity of TFBG cladding resonance wavelengths to the change in the surrounding medium, the sensor is mounted on the steel bar that is embedded in a concreted block during an accelerated corrosion process. The acquired transmission spectrum of the TFBG during the procedure is digitally processed using Fourier Transform to produce an index that is sensitive to the generated corrosion product surrounding the TFBG sensor. This eases the analysis of the sophisticated TFBG transmission spectra. The generated index can be used as an indicator (indicator J ) for the corrosion process of the embedded steel bar in the concrete structure. This indicator J can act as an indicator to describe the corrosion activity and corrosion level at a specific point of the steel bar in concrete structures.
    Źródło:
    Optica Applicata; 2022, 52, 3; 429--439
    0078-5466
    1899-7015
    Pojawia się w:
    Optica Applicata
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Deblurring approach for motion camera combining FFT with α-confidence goal optimization
    Autorzy:
    Huang, Lve
    Wu, Lushen
    Xiao, Wenyan
    Peng, Qingjin
    Powiązania:
    https://bibliotekanauki.pl/articles/174045.pdf
    Data publikacji:
    2020
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    image deblurring
    fast motion camera
    confidence goal optimization
    fast Fourier transform
    high-railway defect detection
    Opis:
    Sharp images ensure success in the object detection and recognition from state-of-art deep learning methods. When there is a fast relative motion between the camera and the object being imaged during exposure, it will necessarily result in blurred images. To deblur the images acquired under the camera motion for high-quality images, a deblurring approach with relatively simple calculation is proposed. An accurate estimation method of point spread function is firstly developed by performing the Fourier transform twice. Artifacts caused by image direct deconvolution are then reduced by predicting the image boundary region, and the deconvolution model is optimized by an α-confidence statistics algorithm based on the greyscale consistency of the image adjacent columns. The proposed deblurring approach is finally carried out on both the synthetic-blurred images and the real-scene images. The experiment results demonstrate that the proposed image deblurring approach outperforms the existing methods for the images that are seriously blurred in direction motion.
    Źródło:
    Optica Applicata; 2020, 50, 2; 185-198
    0078-5466
    1899-7015
    Pojawia się w:
    Optica Applicata
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    A method for probing the refractive index change in photorefractive crystals
    Autorzy:
    Fu, M.
    Gao, C.
    Wang, X.
    Cui, Y.
    Dai, S
    Powiązania:
    https://bibliotekanauki.pl/articles/174913.pdf
    Data publikacji:
    2013
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    Fourier transform profilometry
    refractive index change
    photorefractive effect
    Opis:
    A method for probing refractive index changes in photorefractive crystals using an interferometric technique and digital image processing was proposed. Based on equal thickness interference in LiNbO3 crystal and Fourier transform profilometry, we obtained phase value changes in interferograms induced by a photorefractive effect, and further calculated refractive index changes. The maximal values for extraordinary light (e-light) and ordinary light (o-light) are 6.6×10–4 and 1.2×10–4, respectively.
    Źródło:
    Optica Applicata; 2013, 43, 4; 731-737
    0078-5466
    1899-7015
    Pojawia się w:
    Optica Applicata
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Improved method for phase wraps reduction in profilometry
    Autorzy:
    Du, G.
    Wang, M.
    Zhou, C.
    Si, S.
    Li, H.
    Lei, Z.
    Li, Y.
    Powiązania:
    https://bibliotekanauki.pl/articles/173793.pdf
    Data publikacji:
    2017
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    phase unwrapping
    zero-padding
    Fourier transform
    carrier-frequency
    profilometry
    Opis:
    In order to completely eliminate, or greatly reduce the number of phase wraps in 2D wrapped phase map, Gdeisat and co-workers proposed an algorithm, which uses shifting the spectrum towards the origin. But the spectrum can be shifted only by an integer number, meaning that the phase wraps reduction is often not optimal. In addition, Gdeisat’s method will take much time to make the Fourier transform, inverse Fourier transform, select and shift the spectral components. In view of the above problems, we proposed an improved method for phase wraps elimination or reduction. First, the wrapped phase map is padded with zeros, the carrier frequency of the projected fringe is determined by high resolution, which can be used as the moving distance of the spectrum. And then realize frequency shift in spatial domain. So it not only can enable the spectrum to be shifted by a rational number when the carrier frequency is not an integer number, but also reduce the execution time. Finally, the experimental results demonstrated that the proposed method is feasible.
    Źródło:
    Optica Applicata; 2017, 47, 2; 295-306
    0078-5466
    1899-7015
    Pojawia się w:
    Optica Applicata
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    One shot profilometry using iterative two-step temporal phase-unwrapping
    Autorzy:
    Du, G.
    Wang, M.
    Zhou, C.
    Si, S.
    Li, H.
    Lei, Z.
    Li, Y.
    Powiązania:
    https://bibliotekanauki.pl/articles/173912.pdf
    Data publikacji:
    2017
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    phase unwrapping
    composite fringe pattern
    Fourier transform
    two-step temporal phase-unwrapping
    Opis:
    This paper reviews two techniques that have been recently published for three-dimensional profilometry and proposes one shot profilometry using iterative two-step temporal phase-unwrapping by combining the composite fringe projection and the iterative two-step temporal phase unwrapping algorithm. In temporal phase unwrapping, many images with different frequency fringe pattern are needed to project, which would take much time. In order to solve this problem, Ochoa proposed a phase unwrapping algorithm based on phase partitions using a composite fringe. However, we found that the fringe order determined through the construction of phase partitions tended to be imprecise. Recently, we proposed an iterative two-step temporal phase unwrapping algorithm, which can achieve high sensitivity and high precision shape measurement. But it needs multiple frames of fringe images which would take much time. In order to take into account both the speed and accuracy of three-dimensional shape measurement, we get a new, and more accurate unwrapping method based on a composite fringe pattern by combining these two techniques. This method not only retains the speed advantage of Ochoa’s algorithm, but also greatly improves its measurement accuracy. Finally, the experimental evaluation is conducted to prove the validity of the proposed method.
    Źródło:
    Optica Applicata; 2017, 47, 1; 97-110
    0078-5466
    1899-7015
    Pojawia się w:
    Optica Applicata
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-9 z 9

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