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Oblique astigmatism and field curvature measured with light-field imaging

APPLIED OPTICS 2020年第31期59卷 9710-9714页

作者： Ferreira, Flavio P. Sousa, Marco A. Duarte, Moises A. S. Bret, Boris P. J. Nunes-Pereira, Eduardo J. Univ Minho Ctr Fis Univ Minho & Porto Campus Gualtar P-4710057 Braga Portugal Bosch Secur Syst Sistemas Seguranca SA Estr Nacl 109 IC 1 P-3880728 Aveiro Portugal Bosch Car Multimedia Portugal SA Rua Max Grunding 35 P-4705820 Braga Portugal Univ Minho Dept Fis Campus Gualtar P-4710057 Braga Portugal

The testing of astigmatism and field curvature of an optical system with light-field imaging is proposed. The method consists in measuring the depth map, obtained with a plenoptic camera, of the image of a test pattern formed by the optical system. To demonstrate the accuracy of the method, the virtual image formed by a piano-convex lens was tested. The resulting depth map was compared with the sagittal and tangential foci distances calculated with the Coddington theory. The proposed method could be applied to the quality testing of ocular optics, including eyeglasses, eyepieces, virtual reality goggles, and augmented reality devices. (C) 2020 Optical Society of America

关键词： Augmented reality image processing algorithms Optical aberrations Optical design Optical testing Virtual reality

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Optical topography of rough surfaces using vortex localization of fluorescent markers

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OPTICS LETTERS 2020年第16期45卷 4468-4471页

作者： Schovanek, Petr Bouchal, Petr Bouchal, Zdenek Palacky Univ Dept Opt 17 Listopadu 1192-12 Olomouc 77146 Czech Republic Meopta Optika Sro Kabelikova 1 Prerov 75002 Czech Republic Brno Univ Technol Fac Mech Engn Inst Phys Engn Tech 2 Brno 61669 Czech Republic Brno Univ Technol Cent European Inst Technol Purkynova 656-123 Brno 61200 Czech Republic

Measuring rough surfaces is challenging because the proven topographic methods are impaired by the adverse effects of diffuse light. In our method, the measured surface is marked by fluorescent nanobeads allowing a complete suppression of diffuse light by bandpass filtering. Light emitted by each fluorescent bead is shaped to a double-helix point spread function used for three-dimensional bead localization on the surface. This non-interferometric measurement of rough surface topography is implemented in a vibration resistant setup. The comparison of our method with vertical scanning interferometry shows that a commercial profiler is surpassed when ground glass surfaces with steep slopes are measured. (C) 2020 Optical Society of America

关键词： Bandpass filters Fluorescent markers Green fluorescent protein image processing algorithms Phase unwrapping Vibration

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Fast, sub-pixel accurate, displacement measurement method: optical and terahertz systems

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OPTICS LETTERS 2020年第24期45卷 6611-6614页

作者： Wan, Min Healy, John J. Sheridan, John T. Univ Coll Dublin Coll Architecture & Engn Sch Elect & Elect Engn Dublin 4 Ireland

A novel (to the best of our knowledge), fast method to measure in-plane object motion in 1D with sub-pixel accuracy which complements the correlation technique is proposed. The method is verified experimentally using both visible and terahertz images. The absolute sum of grey level accumulated change is used to quantify object motion. The method requires calibration for each target, but only addition and. subtraction operations. This results in a decrease of two orders of magnitude in the computation time. (C) 2020 Optical Society of America

关键词： Diode pumped lasers image processing algorithms image quality Optical measurement Ptychography Terahertz imaging

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Generative adversarial networks and faster-region convolutional neural networks based object detection in X-ray baggage security imagery

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OSA CONTINUUM 2020年第12期3卷 3604-3614页

作者： Kim, Jongchol Kim, Jiyong Ri, Jinmyong Univ Sci Dept Control Sci Pyongyang 999093 South Korea

X-ray images have now been widely used in public transportation security. However, the ever-increasing number of dangerous object types, along with the complexity of the baggage's contents, makes it unsuitable for clearly displaying various baggages and hazards on X-ray images obtained directly from the inspection system. This article aims to improve the detection of dangerous objects by proposing a data augmentation method for enriching the X-ray prohibited item images using a Generative Adversarial Networks(GANs) based approach. Using the improved GANs model, a new X-ray images were generated with better quality and diversity, and the performance of the proposed method was evaluated using FID(Frechet Inception Distance) score and Faster R-CNN (Region-based Convolutional Neural Network). Experimental results show that the new augmented X-ray security inspection image dataset can improve the detector performance. If other representative training datasets are utilized, we believe that our methodology could aid in the detection of other kinds of threat objects. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： image processing algorithms image quality Neural networks Object detection Vision modeling X ray imaging

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Parallel Fabry-Perot interferometers fabricated on multicore-fiber for temperature and strain discriminative sensing

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OPTICS EXPRESS 2020年第3期28卷 3190-3199页

作者： Zhang, Cong Fu, Songnian Tang, Ming Liu, Deming Huazhong Univ Sci & Technol Wuhan Natl Lab Optoelect Wuhan 430074 Peoples R China Huazhong Univ Sci & Technol Sch Opt & Elect Informat Wuhan 430074 Peoples R China

We experimentally demonstrate parallel Fabry-Perot interferometers (FP's) fabrication in multicore-fiber with individually variable cavity length, for the purpose of discriminative sensing of temperature and strain. First, we theoretically find that, in order to obtain a small condition number of sensitivity matrix, it is necessary to fabricate parallel FPIs with large cavity difference in single multicore fiber. Then, parallel FPIs are inscribed by femtosecond laser selective micro-holes drilling on the seven-core fiber facet, together with fiber fusion splicing process. By the use of image processing algorithm, individual core position is precisely locked, and then parallel FPIs can be obtained on arbitrary two cores of seven-core fiber. With the location of parallel micro-holes and duration time of fiber fusion splicing adjusted, parallel FPIs with different cavity length of 26 mu m and 61 mu m can be simultaneously obtained at the central core and surrounding core, respectively. Consequently, each FPI possesses different sensitivity towards environmental temperature and strain. Finally, a proof-of-concept experiment verifies that relative measurement errors of both temperature and strain discriminative sensing are less than 0.5% and 2.5%, respectively. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： Fabry Perot interferometers Femtosecond fiber lasers Hollow core fibers image processing algorithms Photonic crystal fibers Single mode fibers

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Real-time visible light positioning supporting fast moving speed

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OPTICS EXPRESS 2020年第10期28卷 14503-14510页

作者： Lin, Puxi Hu, Xubin Ruan, Yukui Li, Huaping Fang, Junjian Zhong, Yongchun Zheng, Huadan Fang, Junbin Jiang, Zoe Lin Chen, Zhe Jinan Univ Guangdong Prov Engn Technol Res Ctr VLC Guangzhou Municipal Key Lab Engn Technol VLC Guangzhou 510632 Peoples R China Jinan Univ Dept Optoelect Engn Guangzhou 510632 Peoples R China Peng Cheng Lab Cyberspace Secur Res Ctr Shenzhen 518055 Peoples R China Harbin Inst Technol Shenzhen 518055 Peoples R China

Real-time capability is a key factor which affects the practicality of an indoor positioning system significantly. While visible light positioning (VLP) is widely studied since it can provide indoor positioning functionality with LED illumination, the existing VLP systems still suffer from the high positioning latency and are not practical for mobile units with high moving speed. In this paper, a real-time VLP system with low positioning latency and high positioning accuracy is proposed. With the lightweight image processing algorithm, the proposed system can be implemented on low-cost embedded system and support real-time accurate indoor positioning for mobile units with a fast moving speed. Experimental results show that the proposed system implemented on a Raspberry Pi can achieve a positioning accuracy of 3.93 cm and support the moving speed up to 38.5 km/h. (c) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： image processing image processing algorithms image sensors LED lighting Ultrawideband signals Visible light

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Adaptive exposure control for image-based visual-servo systems using local gradient information

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS image SCIENCE AND VISION 2020年第1期37卷 56-62页

作者： Ding, Zhushun Chen, Xin Jiang, Zhe Tan, Cheng Natl Univ Def Technol Dept Aerospace & Engn Changsha 410073 Peoples R China Beijing Inst Aerosp Control Devices Beijing 100039 Peoples R China

We present anew method for automatic adjustment of camera exposure time for visual-servo systems. The proposed method can improve the robustness of image processing in a high-dynamic-range environment. In this paper, we evaluate an appropriate exposure time by computing the local gradient information of a target area, allowing a camera to capture images without losing target features under artificially adjusted illumination conditions. To validate the advantage of the proposed method, an evaluation is made using an off-the-shelf visual-servo system with a machine vision camera. The experimental results demonstrate the effectiveness of our method, which improves the performance of the target recognition algorithm. (C) 2019 Optical Society of America

关键词： image metrics image processing image processing algorithms image quality Liquid crystals Machine vision

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Automatic production of synthetic labelled OCT images using an active shape model

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IET image processing 2020年第15期14卷 3812-3818页

作者： Danesh, Hajar Maghooli, Keivan Dehghani, Alireza Kafieh, Rahele Islamic Azad Univ Sci & Res Branch Dept Biomed Engn Tehran Iran Isfahan Univ Med Sci Med Image & Signal Proc Res Ctr Sch Adv Technol Med Esfahan Iran Isfahan Univ Med Sci Sch Med Dept Ophthalmol Esfahan Iran

Limited labelled data is a challenge in the field of medical imaging and the need for a large number of them is paramount for the training of machine learning algorithms, as well as measuring the performance of image processing algorithms. The purpose of this study is to construct synthetic and labelled optical coherence tomography (OCT) data to solve the problems of having access to accurately labelled data and evaluating the processing algorithms. In this study, a modified active shape model is used which considers the anatomical features of available images such as the number and thickness of the layers as well as their associated brightness, the location of retinal blood vessels and shadow information with respect to speckle noise. The algorithm is also able to provide different data sets with the varying noise level. The validity of the proposed method for the synthesis of retinal images is measured by two methods (qualitative assessment and quantitative analysis).

关键词： blood vessels biomedical optical imaging optical tomography image segmentation image processing medical image processing learning (artificial intelligence) eye speckle modified active shape model available images retinal blood vessels retinal images automatic production synthetic labelled OCT images medical imaging machine learning algorithms image processing algorithms synthetic coherence tomography labelled optical coherence tomography accurately labelled data

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image-free real-time 3-D tracking of a fast-moving object using dual-pixel detection

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OPTICS LETTERS 2020年第17期45卷 4734-4737页

作者： Deng, Qiwen Zhang, Zibang Zhong, Jingang Jinan Univ Dept Optoelect Engn Guangzhou 510632 Peoples R China

Real-time 3-D tracking of a fast-moving object has found important applications in industry, traffic control, sports, biomedicine, defense, etc. However, it is difficult to adopt typical image-based object tracking systems in a fast-moving object tracking in real time and for a long duration, because reliable and robust image processing and analysis algorithms are often computationally exhausted, and limited storage and bandwidth can hardly fulfill the great demand of high-speed photography. Here we report an image-free 3-D tracking approach. The approach uses only two single-pixel detectors and a high-speed spatial light modulator for data acquisition. By illuminating the target moving object with six single-period Fourier basis patterns, the approach is able to analytically calculate the position of the object with the corresponding single-pixel measurements. The approach is low-cost, and data- and computation-efficient. We experimentally demonstrate that the proposed approach can detect and track a fast-moving object at a frame rate of 1666 frames per second by using a 10,000 Hz digital micromirror device. Benefiting from the wide working spectrum of single-pixel detectors, the reported approach might be applicable for hidden fast-moving object tracking. (C) 2020 Optical Society of America

关键词： Digital micromirror devices High speed photography image processing algorithms Spatial frequency Spatial light modulators Structured illumination microscopy

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How good is your metalens? Experimental verification of metalens performance criterion

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OPTICS LETTERS 2020年第14期45卷 3869-3872页

作者： Engelberg, Jacob Wildes, Talia Zhou, Chen Mazurski, Noa Bar-David, Jonathan Kristensen, Anders Levy, Uriel Hebrew Univ Jerusalem Ctr Nanosci & Nanotechnol Dept Appl Phys IL-91904 Jerusalem Israel Tech Univ Denmark Dept Hlth Technol DK-2800 Lyngby Denmark

A metric for evaluation of overall metalens performance is presented. It is applied to determination of optimal operating spectral range of a metalens, both theoretically and experimentally. This metric is quite general and can be applied to the design and evaluation of future metalenses, particularly achromatic metalenses. (C) 2020 Optical Society of America

关键词： Diffractive lenses image processing algorithms image quality Low light levels Optical design software Optical systems

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