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Suppressing effects of micro-vibration for MTF measurement of high-resolution electro-optical satellite payload in an optical alignment ground facility

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OPTICS EXPRESS 2023年第3期31卷 4942-4953页

作者： Kim, Shinwook Youk, Youngchun Korea Aerosp Res Inst Satellite Payload R&D Div 169-84 Gwahak Ro Daejeon 16984 South Korea

Sensitivity to micro-vibration generated in an optical alignment ground facility increases with the optical aperture of the electro-optical payload mounted on the remote sensing satellite. The micro-vibration distorts the edge spread function (ESF) and changes the modulation transfer function (MTF) value during MTF measurements. Here, an ESF reconstruction network (ESFNet) is proposed to reconstruct the ESF distorted by micro-vibration. A proxy ground-truth ESF dataset for stable training of the proposed ESFNet via a supervised learning method is introduced. The proposed method is robust against both overfitting and underfitting for distorted parts of the ESF caused by micro-vibration. Experiments using ESF obtained in the facility with real micro-vibration show that the measurement error of MTF is around 0.02% when the ESFs are reconstructed using the proposed ESFNet.

关键词： Atmospheric turbulence Digital imaging Imaging noise Modulation transfer function reconstruction algorithms Remote sensing

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Features and Properties of Single-Pixel Imaging Using Speckle Patterns Generated by Multi-Core Fiber

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IEEE ACCESS 2023年 11卷 55326-55333页

作者： Yamaguchi, Ryuta Ikeda, Kanami Koyama, Osanori Yamada, Makoto Osaka Prefecture Univ Grad Sch Engn Osaka 5998531 Japan Osaka Metropolitan Univ Grad Sch Engn Osaka 5998531 Japan

Single-pixel imaging (SPI) has recently drawn considerable attention as a new imaging technique. An SPI system using a multi-core fiber (MCF-SPI system) that we proposed has the potential to make the system very compact. This study is concerned with the features and reconstruction properties of MCF-SPI system. In this system, the reconstruction quality varies widely depending on the number and placement of cores. It is necessary to use reconstruction algorithms suitable for the system, considering the performance limitations of the patterns, to improve the output reconstruction quality. The features and properties of speckle patterns generated by MCFs with different core layouts and algorithms were investigated to improve the reconstruction performance based on numerical simulation. Four existing algorithms were compared under several conditions to evaluate the algorithms that improve reconstruction quality. Compressive sensing based on total variation is the most compatible algorithm for MCF-SPI. It was confirmed that the MCF-SPI system performs well in terms of imaging quality if a suitable core layout and algorithm for the application are set.

关键词： Image reconstruction Layout Entropy TV Imaging reconstruction algorithms Discrete cosine transforms Speckle Single-pixel imaging multi-core fiber image reconstruction compressive sensing

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Mask information-based gamma correction in fringe projection profilometry

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OPTICS EXPRESS 2023年第12期31卷 19478-19490页

作者： Song, Huixin Kong, Lingbao Fudan Univ Sch Informat Sci & Technol Shanghai Engn Res Ctr Ultraprecis Opt Mfg Shanghai 200433 Peoples R China

For fringe projection profilometry (FPP), the gamma effect of the camera and projector will cause non-sinusoidal distortion of the fringe patterns, leading to periodic phase errors and ultimately affecting the reconstruction accuracy. This paper presents a gamma correction method based on mask information. Since the gamma effect will introduce higher-order harmonics into the fringe patterns, on top of projecting two sequences of phase-shifting fringe patterns having different frequencies, a mask image is projected to provide enough information to determine the coefficients of higher-order fringe harmonics using the least-squares method. The true phase is then calculated using Gaussian Newton iteration to compensate for the phase error due to the gamma effect. It does not require projecting a large number of images, and only 2 x 3 phase shift patterns and 1 mask pattern minimum are required. Simulation and experimental results demonstrate that the method can effectively correct the errors caused by the gamma effect. & COPY;2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： Fringe projection Optical measurement Phase compensation Phase shift Phase unwrapping reconstruction algorithms

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Dual-wavelength off-axis digital holography in ImageJ: toward real-time phase retrieval using CUDA streams

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APPLIED OPTICS 2023年第22期62卷 5868-5874页

作者： Zhong, Zhi Song, Diyao Liu, Lei Chen, Xiaolei Shan, Mingguang Harbin Engn Univ Coll Informat & Commun Engn Harbin 150001 Heilongjiang Peoples R China Harbin Engn Univ Natl Key Lab Underwater Acoust Technol Harbin 150001 Peoples R China Beijing Inst Aerosp Control Devices Beijing 100853 Peoples R China

An ImageJ plug-in is developed to realize automatic real-time phase reconstruction for dual-wavelength digital holography (DH). This plug-in assembles the algorithms, including automatic phase reconstruction based on the division algorithm and post-processing. These algorithms are implemented and analyzed using a CPU and GPU, respectively. To hide the CPU-to-GPU data transfer latency, an optimization scheme using Compute Unified Device Architecture (CUDA) streams is proposed in ImageJ. Experimental results show that the proposed plug-in can perform faster reconstruction for dual-wavelength DH, resulting in frame rates up to 48 fps even for onemegapixel digital holograms on a normal PC. In other words, the proposed plug-in can realize real-time phase reconstruction for dual-wavelength digital holographic videos. & COPY;2023 Optica Publishing Group

关键词： Digital holographic imaging Digital image processing Image processing Off axis digital holography Phase retrieval reconstruction algorithms

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High precision 3D imaging with timing corrected single photon LiDAR

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OPTICS EXPRESS 2023年第15期31卷 24481-24491页

作者： Zhang, Cheng Wang, Yupeng Yin, Yongkai Sun, Baoqing Shandong Univ Sch Informat Sci & Engn Qingdao 266237 Peoples R China

Single photon light detection and ranging (LiDAR) is an important technique for high precision long distance three-dimensional (3D) imaging. However, due to the effects and native limitations of system components, there exists ranging errors when using LiDAR system. For the LiDAR system that requires trigger detector to provide synchronization signals, the fluctuation of laser pulse energy causes the change of the initial time of the constant threshold triggered timing module, and subsequently leads to the ranging error. In this paper, we build a dual SPADs LiDAR system to avoid the ranging error caused by the fluctuation of laser pulse energy. By adding a reference optical path, the flight time of signal photons is corrected by reference photons, so as to realize the correction of ranging. A series of experiments demonstrate that the proposed LiDAR system has the capability of high precision ranging and 3D imaging. The system achieves range of error of 0.15 mm and range resolution of 0.3 mm at a distance of 29 m.

关键词： Laser energy Light detection Optical components reconstruction algorithms Remote sensing Three dimensional imaging

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Development and verification of the signal to noise ratio for a layer of turbulence in a multi-layer atmosphere

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION 2023年第3期40卷 573-582页

作者： Hamilton, R. J. Hart, Michael Univ Arizona James C Wyant Coll Opt Sci 1630 E Univ Blvd Tucson AZ 85721 USA

Wide-field image correction in systems that look through the atmosphere generally requires a tomographic recon-struction of the turbulence volume to compensate for anisoplanatism. The reconstruction is conditioned by esti-mating the turbulence volume as a profile of thin homogeneous layers. We present the signal to noise ratio (SNR) of a layer, which quantifies how difficult a single layer of homogeneous turbulence is to detect with wavefront slope measurements. The signal is the sum of wavefront tip and tilt variances at the signal layer, and the noise is the sum of wavefront tip and tilt auto-correlations given the aperture shape and projected aperture separations at all non -signal layers. An analytic expression for layer SNR is found for Kolmogorov and von Karman turbulence models, then verified with a Monte Carlo simulation. We show that the Kolmogorov layer SNR is a function of only layer Fried length, the spatio-angular sampling of the system, and normalized aperture separation at the layer. In addi-tion to these parameters, the von Karman layer SNR also depends on aperture size, and layer inner and outer scales. Due to the infinite outer scale, layers of Kolmogorov turbulence tend to have lower SNR than von Karman layers. We conclude that the layer SNR is a statistically valid performance metric to be used when designing, simulating, operating, and quantifying the performance of any system that measures properties of layers of turbulence in the atmosphere from slope data.

关键词： Deformable mirrors Neural networks Point spread function reconstruction algorithms Visible light Wave front sensing

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Signal restoration algorithm for photoacoustic imaging systems

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BIOMEDICAL OPTICS EXPRESS 2023年第2期14卷 651-666页

作者： Hakakzadeh, Soheil Amjadian, Mohammadreza Zhang, Yachao Mostafavi, Seyed Masood Kavehvash, Zahra Wang, Lidai Sharif Univ Technol Elect Engn Dept Tehran Iran City Univ Hong Kong Dept Biomed Engn Kowloon Hong Kong Peoples R China Hong Kong Univ Sci & Technol Dept Chem & Biol Engn Kowloon Clear Water Bay Hong Kong Peoples R China

In a photoacoustic (PA) imaging system, the detectors are bandwidth-limited. There-fore, they capture PA signals with some unwanted ripples. This limitation degrades the resolution/contrast and induces sidelobes and artifacts in the reconstructed images along the axial direction. To compensate for the limited bandwidth effect, we present a PA signal restoration algorithm, where a mask is designed to extract the signals at the absorber positions and remove the unwanted ripples. This restoration improves the axial resolution and contrast in the reconstructed image. The restored PA signals can be considered as the input of the conventional reconstruction algorithms (e.g., Delay-and-sum (DAS) and Delay-multiply-and-sum (DMAS)). To compare the performance of the proposed method, DAS and DMAS reconstruction algorithms were performed with both the initial and restored PA signals on numerical and experimental studies (numerical targets, tungsten wires, and human forearm). The results show that, compared with the initial PA signals, the restored PA signals can improve the axial resolution and contrast by 45% and 16.1 dB, respectively, and suppress background artifacts by 80%.

关键词： Absorption coefficient Image quality Imaging systems Medical imaging Photoacoustic imaging reconstruction algorithms

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Dual-branch fusion model for lensless imaging

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OPTICS EXPRESS 2023年第12期31卷 19463-19477页

作者： Zhang, Yinger Wu, Zhouyi Xu, Yunhui Huangfu, Jiangtao Zhejiang Univ Lab Appl Res Electromagnet ARE Hangzhou 310027 Peoples R China Kunming Cotech Commun Informat Syst Co Kunming 650106 Peoples R China

A lensless camera is an imaging system that replaces the lens with a mask to reduce thickness, weight, and cost compared to a lensed camera. The improvement of image reconstruction is an important topic in lensless imaging. Model-based approach and pure data-driven deep neural network (DNN) are regarded as two mainstream reconstruction schemes. In this paper, the advantages and disadvantages of these two methods are investigated to propose a parallel dual-branch fusion model. The model-based method and the data-driven method serve as two independent input branches, and the fusion model is used to extract features from the two branches and merge them for better reconstruction. Two types of fusion model named Merger-Fusion-Model and Separate-Fusion-Model are designed for different scenarios, where Separate-Fusion-Model is able to adaptively allocate the weights of the two branches by the attention module. Additionally, we introduce a novel network architecture named UNet-FC into the data-driven branch, which enhances reconstruction by making full use of the multiplexing property of lensless optics. The superiority of the dual-branch fusion model is verified by drawing comparison with other state-of-the-art methods on public dataset (+2.95dB peak signal-to-noise (PSNR), +0.036 structural similarity index (SSIM), -0.0172 Learned Perceptual Image Patch Similarity (LPIPS)). Finally, a lensless camera prototype is constructed to further validate the effectiveness of our method in a real lensless imaging system.

关键词： Fusion Image quality Image reconstruction Imaging systems Neural networks reconstruction algorithms

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Resolution analysis on light-field particle image velocimetry

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION 2023年第4期40卷 729-740页

作者： Zhao, Zhou Yao, Chunhui Shi, Shengxian New, T. H. Shanghai Jiao Tong Univ Sch Mech Engn 800 Dongchuan Rd Shanghai 200240 Peoples R China Nanyang Technol Univ Sch Mech & Aerosp Engn 50 Nanyang Ave Singapore 639798 Singapore

With rapid developments in light-field particle image velocimetry (LF-PIV) based on single-camera, dual-camera, and dual-camera with Scheimpflug lenses, comprehensive quantitative analysis and careful evaluation of their theoretical spatial resolutions are essential to guide their practical applications. This work presents a framework for and better understanding of the theoretical resolution distribution of various optical field cameras with different amounts and different optical settings in PIV. Based on Gaussian optics principles, a forward ray-tracing method is applied to define the spatial resolution and provides the basis of a volumetric calculation method. Such a method requires a relatively low and acceptable computational cost, and can easily be applied in dual-camera/Scheimpflug LF-PIV configuration, which has hardly been calculated and discussed previously. By varying key optical parameters such as magnification, camera separation angle, and tilt angle, a series of volume depth resolution distributions is presented and discussed. By taking advantage of volume data distributions, a universal evaluation criterion based on statistics that is suitable for all three LF-PIV configurations is hereby proposed. With such a criterion, the pros and cons of the three configurations, as well as the effects of key optical parameters, can then be quantitatively illustrated and compared, thus providing useful guidance on the configuration and optical parameter selections in practical implementations of LF-PIV. (c) 2023 Optica Publishing Group

关键词： Cameras First order optics Laser velocimetry Plenoptic imaging reconstruction algorithms Spatial resolution

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Sequential RGB color imaging with a millimeter-scale monochrome camera with a rolling shutter

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APPLIED OPTICS 2023年第17期62卷 4496-4504页

作者： Anspach, Jordan Dickensheets, David L. Montana State Univ Elect & Comp Engn Dept Bozeman MT 59717 USA

Applications are growing for ultracompact millimeter-scale cameras. For color images, these sensors commonly uti-lize a Bayer mask, which can negatively and perceptibly have an impact on image resolution and quality, especially for low pixel-count submillimeter sensors. To alleviate this, we built a time-multiplexed RGB LED illumination system synchronized to the rolling shutter of a monochrome camera. The sequential images are processed and displayed as near real-time color video. Experimental comparison with an identical sensor with a Bayer color mask showed significant improvement in the MTF curves and to perceived image clarity. Trade-offs with respect to system complexity and color motion artifacts are discussed.

关键词： Image processing Image quality Real time implementation reconstruction algorithms Spectral imaging Tunable filters

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