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Central and peripheral refraction measured by a novel double-pass instrument

BIOMEDICAL OPTICS EXPRESS 2023年第6期14卷 2608-2617页

作者： Christaras, Dimitrios Tsoukalas, Spyridon Papadogiannis, Petros Boerjeson, Harlie Volny, Moa Lundstroem, Linda Artal, Pablo Ginis, Harilaos Diestia Syst 77-79 Platonos str Athens 14401 Greece Athens Eye Hosp Dept Res 44 Vouliagmenis Ave Glifadha 17631 Greece Royal Inst Technol Dept Appl Phys S-11421 Stockholm Sweden Univ Murcia Lab Opt Campus EspinardoEdif 34 Murcia 30100 Spain

A novel double-pass instrument and its data analysis method for the measurement of central and peripheral refraction is presented and validated in a group of healthy subjects. The instrument acquires in-vivo, non-cycloplegic, double-pass, through-focus images of the eye's central and peripheral point-spread function (PSF) using an infrared laser source, a tunable lens and a CMOS camera. The through-focus images were analyzed to determine defocus and astigmatism at 0 & DEG;and 30 & DEG;visual field. These values were compared to those obtained with a lab-based Hartmann-Shack wavefront sensor. The two instruments provided data showing good correlation at both eccentricities, particularly in the estimation of defocus.

关键词： Crystalline lens image processing algorithms image quality Infrared lasers Refractive anomalies Refractive surgery

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Process control of laser conduction welding by thermal imaging measurement with a color camera

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APPLIED OPTICS 2005年第32期44卷 6841-6848页

作者： Bardin, F Morgan, S Williams, S McBride, R Moore, AJ Jones, JDC Hand, DP Heriot Watt Univ Sch Engn & Phys Sci Edinburgh EH14 4AS Midlothian Scotland BAE Syst Adv Technol Ctr Bristol BS34 7QW Avon England

Conduction welding offers an alternative to keyhole welding. Compared with keyhole welding, it is an intrinsically stable process because vaporization phenomena are minimal. However, as with keyhole welding, an on-line process-monitoring system is advantageous for quality assurance to maintain the required penetration depth, which in conduction welding is more sensitive to changes in heat sinking. The maximum penetration is obtained when the surface temperature is just below the boiling point, and so we normally wish to maintain the temperature at this level. We describe a two-color optical system that we have developed for real-time temperature profile measurement of the conduction weld pool. The key feature of the system is the use of a complementary metal-oxide semiconductor standard color camera leading to a simplified low-cost optical setup. We present and discuss the real-time temperature measurement and control performance of the system when a defocused beam from a high power Nd:YAG laser is used on 5 mm thick stainless steel workpieces. (c) 2005 Optical Society of America.

关键词： High power diode lasers High power lasers image processing algorithms Laser materials processing Laser welding Thermal infrared imaging

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Accuracy improvement of demodulating the stress field with StressUnet in photoelasticity

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APPLIED OPTICS 2022年第29期61卷 8678-8687页

作者： Zhao, Weiliang Zhang, Guanglei Li, Jiebo Beihang Univ Inst Med Photon Beijing Adv Innovat Ctr Biomed Engn Sch Biol Sci & Med Engn Beijing 100191 Peoples R China

Evaluating the stress field based on photoelasticity is of vital significance in engineering fields. To achieve the goal of efficiently demodulating stress distribution and to overcome the limitations of conventional methods, it is essen-tial to develop a deep learning method to simplify and accelerate the process of image acquisition and processing. A framework is proposed to enhance prediction accuracy. By adopting Resnet as the backbone, applying U-Net architecture, and adding a physical constraint module, our model recovers the stress field with higher structural similarity. Under different conditions, our model performs robustly despite complicated geometry and a large stress range. The results prove the universality and effectiveness of our model and offer an opportunity for instant stress detection. (c) 2022 Optica Publishing Group

关键词： image processing image processing algorithms image quality Medical image processing Optical elements Wave plates

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Comparative study of OCTA algorithms with a high-sensitivity multi-contrast Jones matrix OCT system for human skin imaging

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BIOMEDICAL OPTICS EXPRESS 2022年第9期13卷 4718-4736页

作者： Chen, Guoqiang Wang, Wen'ai Li, Yanqiu Beijing Inst Technol Sch Opt & Photon Key Lab Photoelect Imaging Technol & Syst Minist Educ China 5 South Zhongguancun St Beijing 100081 Peoples R China Beijing Inst Technol Inst Engn Med 5 South Zhongguancun St Beijing 100081 Peoples R China

The multi-contrast Jones matrix OCT (JMT) system can not only improve the tissue -specific contrast but also enhance the sensitivity of detecting flow, which is gaining increasing attention. However, for the JMT system, there is currently a lack of studies evaluating and guiding the selection of suitable angiography algorithms to map the most appealing quality of angiograms for clinical use. In this paper, by a homemade high-sensitivity multi-contrast JMT system based 200 kHz swept source, the performance of two complex-signal-based OCTA methods that are insensitive to phase instability and one amplitude-signal-based OCTA method are compared for in-vivo imaging of human skin qualitatively and quantitatively. Six metrics, including vascular connectivity, image contrast-to-noise ratio, image signal-to-noise ratio, vessel diameter index, blood vessel density, and processing time, are assessed. The results show that the vascular networks processed by all OCTA methods and the texture of skin could be visualized simultaneously and markedly. Additionally, the complex-signal-based OCTA methods successfully suppress phase instabilities and even outperform the amplitude-signal-based OCTA algorithm in some indicators. This paper has a certain guiding significance for selecting an appropriate angiography algorithm and expanding the application field with this system.(c) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： image processing algorithms image quality Imaging techniques In vivo imaging Low coherence interferometry Polarimetric imaging

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Using a visual-attention model when solving problems of autonomous navigation of mobile robots

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JOURNAL OF OPTICAL TECHNOLOGY 2010年第11期77卷 684-689页

作者： Pimenov, V. Yu. St Petersburg State Univ St Petersburg Russia

This paper proposes a model of a visual-attention system and a technique for using it when solving problems of the autonomous navigation of mobile robotic complexes. An analysis is given of known algorithms for localization and mapping of the medium in order to determine factors that affect their operating rate. A model of a visual-attention system is used in order to choose limited regions of input images for processing by localization algorithms and for constructing a map of the medium;this makes it possible to provide the necessary image-processing speed. The results of simulated experiments confirm that the proposed visual-attention model is effective. (C) 2010 Optical Society of America.

关键词： algorithms Analytical techniques High throughput optics image processing image processing algorithms Vision modeling

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Generating vivid colors on red-green-blue-white electronic-paper display

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APPLIED OPTICS 2008年第25期47卷 4491-4500页

作者： Kwak, Youngshin Park, Juyong Park, Du-Sik Park, Jae Byung Samsung Elect SAIT Display Proc Grp Yongin 446712 Gyunggi Do South Korea Samsung Elect LCD Business Flexible Display Lab Giheung South Africa

Color characteristics of an RGBW (red, green, blue, white) electrophoretic display (EPD) prototype developed by Samsung Electronics are analyzed. EPD shows strong crosstalk between subpixels because of both the fringe field between subpixels and the scattering phenomena at the display surface. An RGB-to-RGBW color-decomposition algorithm optimized to EPD characteristics is developed that compensates for color deterioration due to the fringe field and scattering phenomena. For the four-color-decomposition algorithm, white is added to the primary colors to enhance the reflectance of the vivid colors while minimizing chroma loss. The psychophysical experimental result shows that images rendered with the algorithms developed in this study are preferred more than 90% of the time over those rendered with algorithms from previous studies. This research proves that, in spite of the limited physical property of EPD, the color quality can be improved dramatically through the use of well-designed color-rendering algorithms. (C) 2008 Optical Society of America.

关键词： Cathode ray tubes Color rendering Digital imaging image processing algorithms image quality In field scattering

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Phase imaging microscopy under the Gabor regime in a minimally modified regular bright-field microscope

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OPTICS EXPRESS 2021年第26期29卷 42738-42750页

作者： Mico, Vicente Trindade, Karina Angel Picazo-Bueno, Jose Univ Valencia Dept Opt & Optometria & Ciencias Vis C Doctor Moliner 50 Burjassot 46100 Spain

Quantitative phase imaging (QPI) is nowadays a powerful tool for visualization and analysis of biological processes. QPI is usually attained from specifically designed optical microscopes retrieving phase information in a quantitative way. In this paper we report on an extremely simple, low cost and compact way to update a standard bright-field microscope with coherent sensing capabilities. It is based on the in-line Gabor holography concept and only needs to replace the illumination broadband source of the regular microscope with a coherent one. The proposed methodology is completed by the recording of a digital in-line Gabor hologram instead of regular imaging conditions and by the numerical processing of the recorded hologram to finally achieve QPI. The selection of the defocus distance is critical to finally achieve high quality phase imaging, so calibration considering phase and amplitude test targets is presented for the proper definition of such defocus distance. In addition, the selected configuration is experimentally validated using different samples (microbeads, cheek cells and alive spermatozoa). All the experiments are implemented in a regular Olympus BX-60 upright microscope using a 20X 0.46NA objective lens. The proposed method shows how to convert a regular microscope into a holographic one with probably the minimum needed modifications and with the main limitation coming from the Gabor imaging conditions (weak diffractive samples and twin image presence). (C) 2021 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： Digital image processing image processing algorithms image quality Imaging systems Optical microscopy Wave front sensing

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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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Durham adaptive optics real-time controller

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APPLIED OPTICS 2010年第32期49卷 6354-6363页

作者： Basden, Alastair Geng, Deli Myers, Richard Younger, Eddy Univ Durham Dept Phys Durham DH1 3LE England

The Durham adaptive optics (AO) real-time controller was initially a proof of concept design for a generic AO control system. It has since been developed into a modern and powerful central-processing-unit-based real-time control system, capable of using hardware acceleration (including field programmable gate arrays and graphical processing units), based primarily around commercial off-the-shelf hardware. It is powerful enough to be used as the real-time controller for all currently planned 8m class telescope AO systems. Here we give details of this controller and the concepts behind it, and report on performance, including latency and jitter, which is less than 10 mu s for small AO systems. (C) 2010 Optical Society of America

关键词： Atmospheric turbulence Deformable mirrors image processing algorithms image quality Infrared astronomy Laser guide stars

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Employment of Fizeau fringe disintegration to magnify small phase variations

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2020年第11期37卷 A62-A68页

作者： Wahba, Hamdy H. Ramadan, Wael A. El-Tawargy, Ahmed S. Damietta Univ Fac Sci Phys Dept New Damietta Ciiy 34517 Egypt Taif Univ Phys Dept Fac Sci At Taif 21974 Al Haweiah Saudi Arabia

When an object produces a small phase variation not less than the minimum phase variation detectable by the used system and more than the system's noise, the object is considered as a tiny (or small) object. The measurement of interferometric phase differences evolved from a tiny optical phase object has gained attention in recent years due to its usefulness in accurate detection of nanometric dimensions. In the current work, a Fizeau wedge interferometer is used as an aberrationless method to amplify phase variations of a tiny object. The phase object is inserted between the two semi-reflecting/partially transmitting plates making a smallwedge angle in between. The fast Fourier transformation (FFT) spectrum of the obtained interferograms is characterized by some frequency equidistant peaks. The number of these peaks is related to the number of the interfered rays and each peak represents a set of two-beam interferences. We applied a mask to select one of these peaks and reproduced its corresponding optical phase map via employing inverse fast Fourier transformation. The produced map contains the magnified phase variation with a magnification factor equal to 2 times the selected peak's order. Experimental verification of two different phase object samples to amplify their phase variations with different amplification factors is performed. An integrated magnified phase by the object is calculated to test the validity of the proposed method. It is found that the magnification according to the selection of different FFT peaks is a little bit deviated from the expected magnification factors which is referred to ignoring refraction of the optical rays by the object. In spite of these deviations, good results are obtained. (C) 2020 Optical Society of America

关键词： Fizeau interferometry Holographic recording materials image processing algorithms Interferometry Phase measurement Ray tracing

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