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

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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Vehicle positioning scheme based on particle filter assisted single LED visible light positioning and inertial fusion

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OPTICS EXPRESS 2023年第5期31卷 7742-7752页

作者： He, Jing Liu, Yang Hunan Univ Coll Comp Sci & Elect Engn Changsha 410082 Peoples R China

Visible light positioning (VLP) can provide high positioning accuracy based on existing lighting facilities, which gives it great potential for intelligent transportation system (ITS). However, in real scenarios, the performance of visible light positioning is limited by outage problem caused by the sparse distribution of light emitting diode (LED) and time cost of the positioning algorithm. In this paper, a particle filter (PF) assisted single LED VLP (SL-VLP) and inertial fusion positioning scheme is proposed and experimentally demonstrated. It improves the robustness of VLP in sparse LED scenarios. In addition, the time cost and the positioning accuracy at different outage rates and speeds are investigated. The experimental results show that, by using the proposed vehicle positioning scheme, it can achieve the mean positioning error is 0.09 m, 0.11 m, 0.15 m and 0.18 m at 0, 5.5%, 11% and 22% of SL-VLP outage rate, respectively.

关键词： CMOS cameras image processing algorithms image sensors Light detection Positioning equipment Visible light

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Single-shot and phase-shifting digital holographic microscopy using a 2-D grating

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OPTICS EXPRESS 2016年第9期24卷 9480-9488页

作者： Yang, Taeseok Daniel Kim, Hyung-Jin Lee, Kyoung J. Kim, Beop-Min Choi, Youngwoon Korea Univ Sch Biomed Engn Seoul 136701 South Korea Korea Univ Dept Phys Seoul 136701 South Korea

We demonstrate digital holographic microscopy that, while being based on phase-shifting interferometry, is capable of single-shot measurements. A two-dimensional (2-D) diffraction grating placed in a Fourier plane of a standard in-line holographic phase microscope generates multiple copies of a sample image on a camera sensor. The identical image copies are spatially separated with different overall phase shifts according to the diffraction orders. The overall phase shifts are adjusted by controlling the lateral position of the grating. These phase shifts are then set to be multiples of pi/2. Interferograms composed of four image copies combined with a parallel reference beam are acquired in a single shot. The interferograms are processed through a phase-shifting algorithm to produce a single complex image. By taking advantage of the higher sampling capacity of the in-line holography, we can increase the imaging information density by a factor of 3 without compromising the imaging acquisition speed. (C) 2016 Optical Society of America

关键词： Diffraction gratings Holographic microscopy image processing image processing algorithms Phase shift Phase shifting interferometry

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Robust motion-free and error-correcting method of estimating the focal length of a lens

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APPLIED OPTICS 2017年第2期56卷 342-353页

作者： Reza, Syed Azer Anjum, Arslan Lahore Univ Management Sci Dept Elect Engn DHA Phase 2Sect U Lahore 54792 Pakistan Masdar Inst Sci & Technol Dept Elect Engn & Comp Sci Abu Dhabi U Arab Emirates

This paper presents a motion-free technique to characterize the focal length of any spherical convex or concave lens. The measurement test-bench uses a Gaussian laser beam, an electronically controlled variable focus lens (ECVFL), a digital micro-mirror device (DMD), and a standard photo-detector (PD). The method requires measuring beam spot sizes for different focal length settings of the ECVFL and using the measurement data to obtain a focal length estimate through an iterative least-squares-based curve-fitting algorithm. The method is also shown to overcome potential measurement errors that arise due to inaccurate placement of optical components on the test-bench as well as unknown principal plane locations of asymmetric lens samples such as plano-convex lenses. Contrary to the commercially deployed and other proposed methods of focal length characterization, this method does not involve any bulk mechanical motion of optical elements. This approach eliminates measurement errors due to gradual mechanical wear and tear and improves measurement repeatability by minimizing mechanical hysteresis. The compact and fully automated method delivers fast, repeatable, and reliable measurements, which we believe makes it ideal for deployment in industrial lens production units and characterizing lenses used in sensitive imaging systems and various other optical experiments and systems. Measured focal lengths are within the 1% manufacturer-provided tolerance values showing excellent agreement between theory and experiments. We also demonstrate measurement robustness by rectifying discrepancies between known and actual separation distances on the measurement test bench. (C) 2017 Optical Society of America

关键词： image processing algorithms Imaging systems Optical components Optical elements Optical systems Optical testing

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Theoretical model for en face optical coherence tomography imaging and its application to volumetric differential contrast imaging

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BIOMEDICAL OPTICS EXPRESS 2023年第7期14卷 3100-3124页

作者： Tomita, Kiriko Makita, Shuichi Fukutake, Naoki Morishita, Rion Abd El-Sadek, Ibrahim Mukherjee, Pradipta Lichtenegger, Antonia Tamaoki, Junya Bian, Lixuan Kobayashi, Makoto Mori, Tomoko Matsusaka, Satoshi Yasuno, Yoshiaki Univ Tsukuba Computat Opt Grp Tsukuba Japan Nikon Inc Tokyo Japan Damietta Univ Fac Sci Dept Phys Dumyat Egypt Med Univ Vienna Ctr Med Phys & Biomed Engn Vienna Austria Univ Tsukuba Inst Med Dept Mol & Dev Biol Tsukuba Japan Univ Tsukuba Fac Med Clin Res & Reg Innovat Tsukuba Japan

A new formulation of the lateral imaging process of point-scanning optical coherence tomography (OCT) and a new differential contrast method designed by using this formulation are presented. The formulation is based on a mathematical sample model called the dispersed scatterer model (DSM), in which the sample is represented as a material with a spatially slowly varying refractive index and randomly distributed scatterers embedded in the material. It is shown that the formulation represents a meaningful OCT image and speckle as two independent mathematical quantities. The new differential contrast method is based on complex signal processing of OCT images, and the physical and numerical imaging processes of this method are jointly formulated using the same theoretical strategy as in the case of OCT. The formula shows that the method provides a spatially differential image of the sample structure. This differential imaging method is validated by measuring in vivo and in vitro samples.

关键词： Digital image processing image processing image processing algorithms Imaging techniques Interference microscopy Three dimensional imaging

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Perceptually uniform color space for image signals including high dynamic range and wide gamut

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OPTICS EXPRESS 2017年第13期25卷 15131-15151页

作者： Safdar, Muhammad Cui, Guihua Kim, Youn Jin Luo, Ming Ronnier Zhejiang Univ State Key Lab Modern Opt Instrumentat Hangzhou 310027 Zhejiang Peoples R China COMSATS Inst Informat Technol Dept Comp Sci Sahiwal 57000 Pakistan Wenzhou Univ Sch Phys & Elect Informat Engn Wenzhou 325035 Peoples R China Huawei Technol Co Ltd Shanghai 201206 Peoples R China Univ Leeds Sch Design Leeds LS2 9JT W Yorkshire England

A perceptually uniform color space has been long desired for a wide range of imaging applications. Such a color space should be able to represent a color pixel in three unique and independent attributes (lightness, chroma, and hue). Such a space would be perceptually uniform over a wide gamut, linear in iso-hue directions, and can predict both small and large color differences as well as lightness in high dynamic range environments. It would also have minimum computational cost for real time or quasi-real time processing. Presently available color spaces are not able to achieve these goals satisfactorily and comprehensively. In this study, a uniform color space is proposed and its performance in predicting a wide range of experimental data is presented in comparison with the other state of the art color spaces. (C) 2017 Optical Society of America

关键词： CIE color spaces Color difference Color spaces image processing image processing algorithms image quality

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Compact and lightweight panoramic annular lens for computer vision tasks

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OPTICS EXPRESS 2022年第17期30卷 29940-29956页

作者： Gao, Shaohua Sun, Lei Jiang, Qi Shi, Hao Wang, Jia Wang, Kaiwei Bai, Jian Zhejiang Univ State Key Lab Modern Opt Instrumentat Hangzhou 310027 Peoples R China Swiss Fed Inst Technol Comp Vis Lab CH-8092 Zurich Switzerland Zhejiang Univ Natl Engn Res Ctr Opt Instrumentat Hangzhou 310058 Peoples R China

We propose a focal power distribution theory for the design of a compact panoramic annular lens (PAL) system based on Petzval sum correction. The system has a large field of view (FoV) of 360 degrees x(25 degrees-100 degrees). Its total length is 29.2 mm and weight is only 20 g. The proposed compact PAL system achieves large FoV and loose tolerances while maintaining small volume and low cost. It solves the shortcomings of traditional PAL systems that cannot be mounted on miniaturized portable devices due to their large volume and weight. We equip the compact PAL system with a novel and customized image enhancement model: PAL-Restormer to achieve better imaging quality. The produced images are further evaluated in various panoramic environment perception tasks. Extensive experiments show the promising potential of our proposed compact PAL system for the applications in wearable devices and mobile robots. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： image enhancement image processing image processing algorithms image quality Optical systems Spherical lenses

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Plasmon-assisted terahertz imaging inside metal-filled media

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OPTICS EXPRESS 2009年第19期17卷 16456-16464页

作者： Maraghechi, P. Straatsma, C. Liu, Z. Zhao, V. Elezzabi, A. Y. Univ Alberta Dept Elect & Comp Engn Ultrafast Opt & Nanophoton Lab Edmonton AB T6G 2V4 Canada

We present the application of THz plasmonics in imaging dielectric objects embedded in metal-filled media. By exploiting the time domain information from the transmitted pulse, signatures of the objects were observed. To enhance the low quality images acquired through THz time domain spectroscopy, a super-resolution image processing technique was applied. It is shown that pulse arrival time and phase magnitude information compared to the integrated instantaneous power of the transmitted pulse provides more detailed images of the embedded object. (C) 2009 Optical Society of America

关键词： image processing image processing algorithms Imaging systems Imaging techniques Terahertz imaging Terahertz spectroscopy

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Speckle-suppressed full-field imaging through a scattering medium using a supercontinuum

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OPTICS EXPRESS 2016年第23期24卷 26338-26343页

作者： Zheng, Yipeng Si, Jinhai Tan, Wenjiang Ren, Yu Hu Tong, Junyi Hou, Xun Xi An Jiao Tong Univ Sch Elect & Informat Engn Key Lab Phys Elect & Devices Shannxi Key Lab InformatPhoton TechMinist Educ Xianning Xilu 28 Xian 710049 Peoples R China Xian Univ Technol Dept Appl Phys Xian 710048 Peoples R China

We demonstrate speckle-suppressed full-field imaging through a scattering medium using incoherent supercontinuum (SC) illumination. The patterns in images obtained using SC illumination were found to be more easily identifiable than those in images acquired using coherent direct laser illumination due to the speckle suppression. Even when the optical depth reached 12.3, the patterns remained identifiable. As one of the potential applications, we also demonstrated the imaging for a high-pressure diesel spray using SC illumination. (C) 2016 Optical Society of America

关键词： Digital image processing image processing algorithms Imaging systems Optical depth Speckle noise Speckle patterns

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Definition of an error map for DoFP polarimetric images and its application to retardance calibration

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OPTICS EXPRESS 2022年第6期30卷 9534-9547页

作者： Le Teurnier, Benjamin Li, Ning Boffety, Matthieu Goudail, Francois Univ Paris Saclay Lab Charles Fabry Inst Opt Grad Sch CNRS F-91127 Palaiseau France Northwestern Polytech Univ Sch Automat Xian 710072 Peoples R China

With the recent development of division of focal plane (DoFP) polarization sensors, it is possible to perform polarimetric analysis of a scene with a reduced number of acquisitions. One drawback of these sensors is that polarization estimation can be perturbed by the spatial variations of the scene. We thus propose a method to compute a map that indicates where polarization estimation can be trusted in the image. It is based on two criteria: the consistency between the intensity measurements inside a super-pixel and the detection of spatial intensity variations. We design both criteria so that a constant false alarm rate can be set. We demonstrate the benefit of this method to improve the precision of dynamic retardance calibration of DoFP-based full Stokes imaging systems. (C) 2022 Optics Publishing Group under the terms of the Optics Open Access Publishing Agreement

关键词： Calibration Edge detection image processing algorithms Imaging systems Polarimetric imaging Polarization

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