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Solar eclipse skies and limb reddening

APPLIED OPTICS 2020年第21期59卷 F78-F84页

作者： Gedzelman, Stanley David CUNY City Coll Dept Earth & Atmospher Sci New York NY 10031 USA CUNY City Coll NOAA CREST Ctr New York NY 10031 USA

During solar eclipses the sunlit tops of cloud layers and arctic sea ice near the umbra appear salmon-brown when viewed from airplanes or satellites. Under these conditions, the clouds and atmosphere are illuminated by light restricted to the solar limb, which has effective radiating temperatures as low as 4000 K. The resulting limb reddening largely accounts for the color. A second-order scattering model is used to simulate the color of photographs of cloud tops taken from a flight during the 21 August 2017 eclipse and MODIS Aqua and Terra satellite "true color" images during the 2 July 2019 eclipse. These observed color changes provide data that has potential value in determining the vertical temperature profile of the solar photosphere. (C) 2020 Optical Society of America

关键词： Blackbodies image processing algorithms Light wavelength Optical depth Rayleigh scattering Visible light

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image restoration for synthetic aperture systems with a non-blind deconvolution algorithm via a deep convolutional neural network

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OPTICS EXPRESS 2020年第7期28卷 9929-9943页

作者： Hui, Mei Wu, Yong Li, Weiqian Liu, Ming Dong, Liquan Kong, Lingqin Zhao, Yuejin Beijing Inst Technol Sch Optoelect Beijing Key Lab Precis Optoelect Measurement Inst Beijing 100081 Peoples R China

Optical synthetic aperture imaging systems, which consist of in-phase circular submirrors, can greatly improve the spatial resolution of a space telescope. Due to the sub-mirrors' dispersion and sparsity, the modulation transfer function is decreased significantly compared to a fully filled aperture system, which causes obvious blurring and loss of contrast in the collected image. image restoration is the key to get the ideal clear image. In this paper, an appropriative non-blind deconvolution algorithm for image restoration of optical synthetic aperture systems is proposed. A synthetic aperture convolutional neural network (CNN) is trained as a denoiser prior to restoring the image. By improving the half-quadratic splitting algorithm, the image restoration process is divided into two subproblems: deconvolution and denoising. The CNN is able to remove noise in the gradient domain and the learned gradients are then used to guide the image deconvolution step. Compared with several conventional algorithms, scores of evaluation indexes of the proposed method are the highest. When the signal to noise ratio is 40 dB, the average peak signal to noise ratio is raised from 23.7 dB of the degraded images to 30.8 dB of the restored images. The structural similarity index of the results is increased from 0.78 to 0.93. Both quantitative and qualitative evaluations demonstrate that the proposed method is effective. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： image deconvolution image processing image processing algorithms Imaging systems Optical transfer functions Synthetic aperture imaging

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Athermalization of dual-waveband infrared systems containing diffractive optical elements via optical-digital joint design

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APPLIED OPTICS 2020年第4期59卷 1212-1216页

作者： Hu, Yang Cui, Qingfeng Sun, Lin Zhang, Bo Changchun Univ Sci & Technol Sch Optoelect Engn Changchun 130022 Peoples R China

Because of material limitations, achieving an athermal design for dual-waveband infrared systems is difficult. This study integrates single-layer diffractive elements to reduce the volume and weight of such a design and introduces optical-digital joint methods to eliminate the impact of low diffraction efficiency. To achieve athermalization, temperature polychromatic integral diffraction efficiency and temperature integral wavelength weight are incorporated in the point spread function (PSF) model. Influence of low diffraction efficiency is eliminated via subsequent algorithm processing. Accordingly, athermal design and processing of a cooled dual-waveband infrared system is achieved and verified via experimental results. (C) 2020 Optical Society of America

关键词： Diffraction efficiency Diffractive optical elements image processing image processing algorithms image quality Infrared systems

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Spatial frequency-based angular behavior of a short-range flicker-free MIMO-OCC link

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APPLIED OPTICS 2020年第33期59卷 10357-10368页

作者： Teli, Shivani Rajendra Zvanovec, Stanislav Perez-Jimenez, Rafael Ghassemlooy, Zabih Czech Tech Univ Fac Elect Engn Dept Electromagnet Field Prague 16627 Czech Republic Univ Las Palmas Gran Canaria IDeTIC Las Palmas Gran Canaria 35001 Spain Northumbria Univ Fac Engn & Environm Opt Commun Res Grp Newcastle Upon Tyne NE1 7RU Tyne & Wear England

In this paper, we provide a solution based on spatial frequency f(sf) to study the angular behavior of a flicker-free, short-range indoor multiple-input multiple-output (MIMO) optical camera communications (OCC) link. We focus on the experimental investigation of OCC's performance for the transmitters (Txs) [i.e., light-emitting diode (LED) based arrays] located at the same and different distances from the receiver (Rx) with the off-axis rotation angle theta. We have used two 8 x 8 distributed LED arrays and a commercial low-cost complementary metal-oxide-semiconductor (CMOS) Raspberry Pi camera with the rolling-shutter capturing mode as the Tx and Rx, respectively. The image and the respective communications link quality metrics are measured in terms of the peak signal-to-noise ratio (PSNR) and the rate of successfully received bits with respect to f(sf) for different camera shutter speeds (SS). A CMOS image sensor noise characterization is carried in terms of the signal-to-noise ratio (SNR) and PSNR. The proposed study provides a 100% success rate in data reception at the optimum theta of 50 degrees at lower captured values of f(sf), which is projected onto the image sensor in the form of pixels. Moreover, the effect of channel saturation over f(sf) is studied with respect to theta and SS and we show that, for theta exceeding the optimum value along transmission range, the f(sf) area of the Txs reduces to less than similar to 50% of the captured Tx units at theta of 0 degrees, where no data can be fully recovered. (C) 2020 Optical Society of America

关键词： High speed photography image processing algorithms image sensors Imaging noise Quadrature amplitude modulation Spatial frequency

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Improving the visible light communication localization system using Kalman filtering with averaging

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2020年第11期37卷 A130-A138页

作者： Shawky, Eman El-Shimy, Mohamed Mokhtar, Amr El-Badawy, El-Sayed A. Shalaby, Hossam M. H. Alexandria Univ Fac Engn Elect Engn Dept Alexandria 21544 Egypt Egypt Japan Univ Sci & Technol E JUST Dept Elect & Commun Engn Alexandria 21934 Egypt

Two techniques are proposed for improving the accuracy of localization estimation in indoor visible light communication systems, namely, averaging and Kalman filtering with averaging schemes. In the averaging technique, the receiver position is estimated using the received signal strength (RSS) indication method multiple times (e.g., N samples), and the acquired estimations are averaged over all samples. To further improve the localization, the Kalman filtering algorithm is adopted to estimate the received power over N samples, followed by applying the RSS technique on the average received power. The proposed techniques are analyzed mathematically, considering the effects of both line-of-sight (LOS) and first-reflection from non-LOS propagations. The performance of the proposed techniques is determined by evaluating the positioning errors in a typical room. The results are compared to that of the traditional RSS system. Simulation results reveal that an improvement of about 33.3% in the average positioning error is achievable when using the averaging scheme as compared to that of the traditional RSS scheme. This improvement increases to 72.2% when adopting the proposed Kalman filtering scheme. (C) 2020 Optical Society of America

关键词： image processing algorithms Optical signals Optical wireless communication Phase measurement Visible light Visible light communications

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Three-dimensional collagen fiber mapping and tractography of human uterine tissue using OCT

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BIOMEDICAL OPTICS EXPRESS 2020年第10期11卷 5518-5541页

作者： McLean, James P. Fang, Shuyang Gallos, George Myers, Kristin M. Hendon, Christine P. Columbia Univ Dept Elect Engn New York NY 10027 USA Columbia Univ Dept Mech Engn New York NY 10027 USA Columbia Univ Irving Med Ctr Dept Anesthesiol New York NY 10032 USA

Automatic quantification and visualization of 3-D collagen fiber architecture using Optical Coherence Tomography (OCT) has previously relied on polarization information and/or prior knowledge of tissue-specific fiber architecture. This study explores image processing, enhancement, segmentation, and detection algorithms to map 3-D collagen fiber architecture from OCT images alone. 3-D fiber mapping, histogram analysis, and 3-D tractography revealed fiber groupings and macro-organization previously unseen in uterine tissue samples. We applied our method on centimeter-scale mosaic OCT volumes of uterine tissue blocks from pregnant and non-pregnant specimens revealing a complex, patient-specific network of fibrous collagen and myocyte bundles. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： High speed imaging image processing image processing algorithms image quality Second harmonic generation Three dimensional imaging

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Diagnosis of liquid-gas mixed sprays in the near-field region using femtosecond laser induced supercontinuum imaging method

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OPTICS EXPRESS 2020年第3期28卷 3298-3304页

作者： Wang, Mingxin Tan, Wenjiang Si, Jinhai Zheng, Yipeng Huang, Zhenqiang Xi An Jiao Tong Univ Key Lab Phys Elect & Devices Minist Educ Shannxi Key Lab Informat Photon TechSch Elect Sc Xianning Xilu 28 Xian 710049 Peoples R China

Direct femtosecond shadowgraphy and supercontinuum (SC)-illumination imaging methods for diagnosing liquid-gas mixed sprays in the near-field region of spray nozzles were compared. Some big spray structures can be captured using femtosecond shadowgraphy which can freeze the motion of the sprays. But the speckles caused by the interference of multi-scattered photons erode the edges of ligaments and conceal many fine droplets. SC-illumination imaging can not only freeze the motion of the sprays but also significantly suppressing the speckles, presenting a more realistic spray pattern. Based on the SC imaging technology, the effects of various factors such as flow ratio of gas to liquid (GLR), total flow and nozzle size on the spray were studied. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： Digital image processing image processing algorithms image quality Imaging systems Imaging techniques Speckle patterns

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Reconstruction of high-resolution 6 x 6-mm OCT angiograms using deep learning

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BIOMEDICAL OPTICS EXPRESS 2020年第7期11卷 3585-3600页

作者： Gao, Min Guo, Yukun Hormel, Tristan T. Sun, Jiande Hwang, Thomas S. Jia, Yali Oregon Hlth & Sci Univ Casey Eye Inst Portland OR 97239 USA Shandong Normal Univ Sch Informat Sci & Engn Jinan 250358 Peoples R China Oregon Hlth & Sci Univ Dept Biomed Engn Portland OR 97239 USA

Typical optical coherence tomographic angiography (OCTA) acquisition areas on commercial devices are 3x3- or 6x6-mm. Compared to 3x3-mm angiograms with proper sampling density, 6x6-mm angiograms have significantly lower scan quality, with reduced signal-to-noise ratio and worse shadow artifacts due to undersampling. Here, we propose a deep-learning-based high-resolution angiogram reconstruction network (HARNet) to generate enhanced 6x6-mm superficial vascular complex (SVC) angiograms. The network was trained on data from 3x3-mm and 6x6-mm angiograms from the same eyes. The reconstructed 6x6-mm angiograms have significantly lower noise intensity, stronger contrast and better vascular connectivity than the original images. The algorithm did not generate false flow signal at the noise level presented by the original angiograms. The image enhancement produced by our algorithm may improve biomarker measurements and qualitative clinical assessment of 6x 6-mm OCTA. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： image enhancement image processing image processing algorithms image quality image reconstruction Retinal nerve fiber layer

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Detection of visual defects on rotationally symmetric objects

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS image SCIENCE AND VISION 2020年第10期37卷 1583-1594页

作者： Smid, Petr Havranek, Vitezslav Ivanov, Georgi Palacky Univ FZU Inst Phys Joint Lab Opt Czech Acad Sci 17 Listopadu 12 Olomouc 77146 Czech Republic Acad Sci Czech Republ Inst Phys 17 Listopadu 12 Olomouc 77146 Czech Republic Palacky Univ Joint Lab Opt 17 Listopadu 12 Olomouc 77146 Czech Republic Palacky Univ Olomouc Inst Phys Acad Sci Czech Republ Fac Sci 17 Listopadu 12 Olomouc 77146 Czech Republic

The paper describes a method using digital image processing in the detection of vaguely defined visual defects on objects symmetric with respect to a rotation axis. Automotive wheels and hubcaps, fans, turbines, symmetrical ceramic goods, merchandise, etc., are examples of such objects. The method uses the object's surface symmetry to identify areas that do not meet the requirement for the symmetry. The method is based on the brightness comparison of areas of the object's surface under test corresponding to each other with respect to the object's rotational symmetry. The area containing a defect is located through the difference between its brightness and average brightness of the all symmetric areas. The reliability of the method requires opaque and not too broken surfaces with solitary defects that do not overlap when the object is rotated. The method is advantageous for larger defects. Minimum defect size is limited by segmentation of the object and its production tolerances. Uniform illumination is another prerequisite for the reliable detection of the defects. This work focuses on testing the method and determination of the optimum brightness difference characterizing the defect. Next, limitations of the method are analyzed, especially the relationship between the uncertainty of the object shape, the camera resolution, and the minimum size of the detected defect. (C) 2020 Optical Society of America

关键词： Digital image processing Holographic interferometry image processing algorithms Laser beams LED lenses Phase shift

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Procedure for detecting the shape and size of defects on metallic substrates under composite repairs using shearography

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APPLIED OPTICS 2020年第27期59卷 8089-8097页

作者： Felipe, Diego Staub Benedet, Mauro Fantin, Analucia Vieira Willemann, Daniel Pedro Fonseca Martins, Fabiana Dias Fampa Seabra D'Almeida, Ana Lucia Soares, Sergio Damasceno Goncalves Jr, Armando Albertazzi Lenzi, Arcanjo Univ Fed Santa Catarina 5053 Univ Campus Florianopolis SC Brazil Univ Estado Santa Catarina 2007 Itacorubi Florianopolis SC Brazil CENPES Petrobras Rio De Janeiro RJ Brazil

This paper presents a numerical-experimental procedure to characterize through-holes with arbitrary shapes present on metallic substrates under composite material sleeves using pulsed laser shearography and dynamic excitation combined to the finite element method. The so-called fitting process consists of matching experimental and numerical results in order to determine the shape and dimensions of the holes under the composite repair, or even quantify defects between layers of the composite laminate. The results show that the technique is capable of characterizing, in the worst case, the geometry of a hole with 83% accuracy and its respective area with a maximum error of approximately 20%. The advantageous results achieved in this research show that the fitting process can be very useful for real applications in the oil and petroleum industry. (C) 2020 Optical Society of America

关键词： Composite materials image processing algorithms Industrial optical metrology Interferometry Michelson interferometers Pulsed operation

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