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Optimization of stereoscopic imager performance by computer simulation of geometrical calibration using optical design software

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OPTICS EXPRESS 2019年第13期27卷 17819-17839页

作者： Gorevoy, Alexey, V Machikhin, Alexander S. Batshev, Vladislav, I Kolyuchkin, Vasiliy Ya Russian Acad Sci Sci & Technol Ctr Unique Instrumentat Lab Acoustoopt Spect 15 Butlerova Str Moscow 117342 Russia Natl Res Univ Moscow Power Engn Univ Inst Automat & Comp Engn Dept Elect Engn & Introscopy 14 Krasnokazarmermaya Str Moscow 111250 Russia Bauman Moscow State Tech Univ Dept Radioelect & Laser Technol 5 2 Ya Baumanskaya Str Moscow 105005 Russia

Stereoscopic imagers are widely used in machine vision for three-dimensional (3D) visualization as well as in non-destructive testing for quantitative characterization of cracks, delamination and other defects. Measurement capability in these systems is provided by a proper combination of the optical parameters and data processing techniques. Conventional approach to their design consists of two sequential stages: optical system design and optimization of calibration and image processing algorithms. Such two-stage procedure often complicates both the hardware and the software, and results in a time-ineffective design procedure and cost-ineffective solution. We demonstrate a more effective approach and propose to estimate errors of 3D measurements at the early optical design stage. We show that computer simulation using optical design software allows not only optimizing optical parameters of the imager but also choosing the most effective mathematical model of the system and the equipment necessary for calibration. We tested the proposed approach on the design of miniature prism-based stereoscopic system and analyzed the impact of various factors (aberrations, tolerances, etc.) as on the image quality, so on the quality of calibration and 3D measurements accuracy. The proposed joint design approach may be highly effective for various measurement systems and applications when both optical parameters and image processing algorithms are not defined in advance and are necessary to be optimized. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： Camera calibration Digital image processing image processing algorithms image quality Optical design software Optical systems

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Inverse synthetic aperture ladar autofocus imaging algorithm for micro-vibrating satellites based on two prominent points

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APPLIED OPTICS 2019年第25期58卷 6775-6783页

作者： Song, Zi-Qi Mo, Di Wang, Ning Li, Bing-Chen Shao, Yong-She Tan, Rong-Qing Univ Chinese Acad Sci Sch Elect Elect & Commun Engn Beijing 100049 Peoples R China Chinese Acad Sci Inst Elect Beijing 100190 Peoples R China

As an important imaging method for long-range satellite targets, inverse synthetic aperture ladar (ISAL) has the characteristics of high-resolution imaging and competitive detectability. Since the working wavelength of the ISAL is comparable to the micro-vibrations generated by mechanical moving components of satellites, which will cause image defocusing, motion compensation is of great significance. In this paper, an autofocus algorithm is proposed for estimating and compensating the phase error relating to both translational and rotational micro-vibrations. Comparing with non-parametric algorithms like phase gradient autofocus and parametric algorithms like contrast-based autofocus and entropy-based autofocus, the proposed one, which is based on two prominent points, is especially effective for the rotational phase error oscillating numbers of cycles. Simulations and experiments are conducted to validate the feasibility of the proposed algorithm. (C) 2019 Optical Society of America

关键词： Aperture synthesis image processing algorithms image quality Imaging techniques Power spectral density Synthetic aperture radar

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Full-spectrum denoising of high-SNR hyperspectral images

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS image SCIENCE AND VISION 2019年第3期36卷 450-463页

作者： Colom, Miguel Morel, Jean-Michel Univ Paris Saclay ENS Paris Saclay CNRS Ctr Math & Leurs Applicat F-94235 Cachan France

The high spectral redundancy of hyper/ultraspectral Earth-observation satellite imaging raises three challenges: (a) to design accurate noise estimation methods, (b) to denoise images with very high signal-to-noise ratio (SNR), and (c) to secure unbiased denoising. We solve (a) by a new noise estimation, (b) by a novel Bayesian algorithm exploiting spectral redundancy and spectral clustering, and (c) by accurate measurements of the interchannel correlation after denoising. We demonstrate the effectiveness of our method on two ultraspectral Earth imagers, IASI and IASI-NG, one flying and the other in project, and sketch the major resolution gain of future instruments entailed by such unbiased denoising. (C) 2019 Optical Society of America

关键词： Blackbodies Hyperspectral imaging image processing algorithms Material characterization Multispectral imaging Wavelet transforms

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Alignment strategy for an optomechanical image derotator using a laser Doppler vibrometer

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APPLIED OPTICS 2019年第24期58卷 6555-6568页

作者： Altmann, Bettina Betker, Tim Pape, Christian Reithmeier, Eduard Leibniz Univ Hannover Inst Measurement & Automat Control Nienburger Str 17 D-30167 Hannover Germany

When monitoring the condition of technical components, it is of particular interest to obtain information of the current condition of the component during operation. The main objectives are safety and machine efficiency. A special extension in this area is the derotator, since the derotator can be used to extend measuring methods designed for static components to rotating systems. In this paper, we present a new, to the best of our knowledge, approach to align a derotator using a laser Doppler vibrometer (LDV). When aligning the derotator, the optical axis must be coaxial with the rotating object to be measured. Current conventional approaches only ensure that the optical axis and the rotational axis intersect at the center of the measuring object. In our approach, a LDV is used to determine the angular deviation between the two axes, which cannot be determined by common methods. Our approach is easy to implement because the LDV is often already used in combination with the derotator as a measuring device. Experiments are carried out to show that this approach is feasible. In addition, several investigations are being performed to analyze how different parameters affect the result, creating reproducible conditions and deriving an alignment approach. By combining the approach developed in this work for determining a rotational deviation with common image-based approaches for determining a translational deviation of the axes, the derotator can be calibrated entirely. In this way, the quality of the measurement with the derotator can be further increased, as calibration errors can be reduced. (C) 2019 Optical Society of America

关键词： image processing image processing algorithms Light beams Metrological instrumentation Optical components Speckle patterns

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Assessment of VINO filters for correcting red-green Color Vision Deficiency

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OPTICS EXPRESS 2019年第13期27卷 17954-17967页

作者： Martinez-Domingo, Miguel A. Gomez-Robledo, Luis Valero, Eva M. Huertas, Rafael Hernandez-Andres, Javier Ezpeleta, Silvia Hita, Enrique Univ Granada Dept Opt Granada Spain

In our ongoing research on the effectiveness of different passive tools for aiding Color Vision Deficiency (CVD) subjects, we have analyzed the VINO 02 Amp Oxy-Iso glasses using two strategies: 1) 52 observers were studied using four color tests (recognition, arrangement, discrimination, and color-naming);2) the spectral transmittance of the lenses were used to model the color appearance of natural scenes for different simulated CVD subjects. We have also compared VINO and EnChroma glasses. The spectral transmission of the VINO glasses significantly changed color appearance. This change would allow some CVD subjects, above all the deutan ones, to be able to pass recognition tests but not the arrangement tests. To sum up, our results support the hypothesis that glasses with filters are unable to effectively resolve the problems related to color vision deficiency. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： Color spaces Color vision image processing algorithms Low light levels Standard observers Visual acuity

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Micrometric size measurement of biological samples using a simple and non-invasive transmission interferometric set up

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OPTICS EXPRESS 2019年第19期27卷 26251-26263页

作者： Frausto-Rea, Gloria De la Torre, Manuel H. Flores, J. Mauricio Silva, Luis Briones-R, Manuel Mendoza Santoyo, F. Ctr Invest Opt Unidad Aguascalientes Prol Constituc 607 Aguascalientes 20200 Ags Mexico Ctr Invest Opt Unidad Leon Loma Del Bosque 115 Guanajuato 37150 Mexico Inst Tecnol Jose Mario Molina Pasquel y Henriquez Libramiento Tec 5000 Lagos De Moreno 47480 Jalisco Mexico

An interferometer with a minimum of optical hardware is employed to measure invasiveness the size of biological samples. Nowadays, there are several techniques in microscopy that render high quality resolved images. For instance, consider optical microscopy that has been around for over a century and has since developed in different configurations such as: bright and dark field, phase contrast, confocal, polarized, and so on. However, only a few of these use interferometry to retrieve not only the sample's amplitude but also its phase. An interesting example of the latter is digital holography which normally uses a Mach Zehnder interferometer setup. In the research work reported here a transmission digital holographic interferometer designed with a simple and minimal optical hardware, that avoids the drawback of the small field of view present in classical optical microscopic systems, is used to measure the microscopic dimensions of pollen grains. This optical configuration can be manipulated to magnify and project the image of a semitransparent sample over a neutral phase screen. The use of a collimated beam through the sample prevents geometrical distortions for high magnification values. The measurements using this novel configuration have been validated using a standard precision pattern displacement specimen with certified dimensions. As proof of principle, microscopically characterized pollen grains are placed in the transmission set up in order to estimate their dimensions from the interferometrically retrieved optical phase. Results match and thus show a relation between the sample's size and the optical phase magnitude. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： image processing image processing algorithms image quality Multiphoton microscopy Near field microscopy Wavefront distortions

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Radiometric calibration methods for day/night whole sky imagers and extinction imagers

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APPLIED OPTICS 2019年第21期58卷 5663-5673页

作者： Shields, Janet E. Karr, Monette E. Univ Calif San Diego Scripps Inst Oceanog Marine Phys Lab 9500 Gilman Dr La Jolla CA 92093 USA

This paper discusses the new radiometric calibration methods and results that we have developed to apply to day/ night whole sky imager data and extinction imager data. Day/night whole sky imagers detect the presence and location of clouds and categorize them by opacity. The new day and night doud algorithms for these instruments are documented elsewhere, and these algorithms depend on the use of the new calibrations we have developed. In this paper, we document our calibration methods for determining the absolute radiance of the whole sky imager scene at each pixel in the images as well as the results of the calibrations. The extinction imagers are new systems we developed that determine beam transmittance and path extinction for horizontal paths through the atmosphere. These instruments and their algorithms are documented elsewhere, and they also depend on the new calibration results. The extinction imager algorithms only require relative radiances, as opposed to absolute radiances. The calibration steps for the two instruments are quite similar, and they include dark correction;linearity calibration, which corrects for nonlinearities in the signal versus flux relationship;absolute calibration (for the whole sky imager);and uniformity calibration, which corrects for pixel-to-pixel nonuniformities. These developments include methods for handling uniformity calibrations in a system using a fisheye lens and the calibration of both visible and short-wave IR systems. This paper presents both the new methods and results in support of the papers documenting the algorithms. (C) 2019 Optical Society of America

关键词： Atmospheric optics Extinction coefficients image processing algorithms Infrared systems Low light levels Radiometric calibration

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Precision optical path alignment system for point diffraction interferometer based on image information

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APPLIED OPTICS 2019年第14期58卷 3703-3711页

作者： Zhao, Zhuo Li, Bing Kang, Xiaoqin Chen, Lei Wei, Xiang Xi An Jiao Tong Univ State Key Lab Mfg Syst Engn 99 Yanxiang Rd Xian 710054 Shaanxi Peoples R China Xi An Jiao Tong Univ Int Joint Res Lab Micro Nano Mfg & Measurement Te Xian 710049 Shaanxi Peoples R China

In a point diffraction interferometer, the existence of alignment error between an objective convergent spot and a diffraction pinhole can lead to wavefront error and diffraction intensity reduction. Meanwhile, the contrast of the point diffraction interferograms probably decreases in this procedure. These changes will have significant influence on its inspection precision. A precise alignment system of an optical path for a point diffraction interferometer is proposed in this paper. First, diffraction theory is used to analyze the mathematical relationships of alignment error to diffraction wavefront error and numerical aperture and wavefront error to pinhole size. Then, according to the requirement, the scheme of an optical path alignment system is designed. In this stage, alignment images as well as intensities of a reflected and diffracted beam from the point diffraction plate will be acquired. In addition, an image processing algorithm for measuring alignment error is designed, and a mathematical model between quantities of measurement and control is constructed. Finally, implementation and experiment of this method are also introduced. Misalignment situations, including lateral translation, longitudinal defocus, and tilt error, are well eliminated, and the quality of interferograms is also improved. From the results, it can be concluded that the system is of desirable precision and efficiency. (C) 2019 Optical Society of America

关键词： Diffraction theory Extreme ultraviolet lithography image processing algorithms Optical elements Point diffraction interferometry Power spectral density

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47-kbit/s RGB-LED-based optical camera communication based on 2D-CNN and XOR-based data loss compensation

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OPTICS EXPRESS 2019年第23期27卷 33841-33847页

作者： Liu, Liqiong Deng, Rui Chen, Lian-Kuan Chinese Univ Hong Kong Dept Informat Engn Shatin Hong Kong Peoples R China

In an RGB-LED-based optical camera communication (OCC) system, the inter-symbol interference and inter-channel interference deteriorate the transmission performance considerably. In this paper, a two-dimensional CNN structure is proposed for data recovery by learning features between color channels and neighboring symbols in the rolling shutter based OCC system under random data transmission. Moreover, we further propose an XOR-based data loss compensation method to realize 21% data rate improvement by restoring the lost data during the transmission. A record-high data rate at 47 kbit/s has been experimentally achieved for an RGB-LED-based OCC system using a rolling shutter camera in a smartphone. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： Bit error rate Face recognition image processing algorithms Machine vision Neural networks Pattern recognition

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Improving reconstruction of speckle correlation imaging by using a modified phase retrieval algorithm with the number of nonzero-pixels constraint

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APPLIED OPTICS 2019年第2期58卷 473-478页

作者： Liao, Meihua Lu, Dajiang He, Wenqi Pedrini, Giancarlo Osten, Wolfgang Peng, Xiang Shenzhen Univ Coll Optoelect Engn Key Lab Optoelect Devices & Syst Educ Minist China Shenzhen Peoples R China Univ Stuttgart Inst Tech Opt Pfaffenwaldring 9 D-70569 Stuttgart Germany

Speckle correlation imaging (SCI) has been considered one of the most promising techniques for computational imaging through a scattering medium. However, the image quality is not always acceptable in conventional SCI, especially when a complex object is involved. In this work, a modified phase retrieval algorithm is introduced to significantly improve the imaging quality of SCI. In the proposed scheme, nonzero-pixel constraints, rather than the real and nonnegative constraints, are employed as the object domain constraints of the iterative algorithm in the image reconstruction process. Experimental results are presented to show the performance enhancement of this scheme, inclusive of less iterations, better image quality, and higher reliability, in comparison with the conventional SCI method. (C) 2019 Optical Society of America

关键词： image processing algorithms image quality Phase retrieval Scattering media Speckle patterns Zernike polynomials

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