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Automated calibration of multi-camera-projector structured light systems for volumetric high-speed 3D surface reconstructions

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OPTICS EXPRESS 2018年第25期26卷 33278-33304页

作者： Deetjen, Marc E. Lentink, David Stanford Univ Dept Mech Engn Stanford CA 94305 USA

It is challenging to calibrate multiple camera-projector pairs for multi-view 3D surface reconstruction based on structured light. Here, we present a new automated calibration method for high-speed multi-camera-projector systems. The method uses printed and projected dot patterns on a planar calibration target, which is moved by hand in the calibration volume. Calibration is enabled by automated image processing and bundle-adjusted parameter optimization. We determined the performance of our method by 3D reconstructing a sphere. The accuracy is -0.03 +/- 0.09 % as a percentage of the diameter of the calibration volume. Applications include quality control, autonomous systems, engineering measurements, and motion capture, such as the preliminary 3D reconstruction of a bird in flight we present here. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： Camera calibration image processing image processing algorithms Reconstruction algorithms Stray light Three dimensional image processing

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Approach for recognizing and tracking beacon in inter-satellite optical communication based on optical flow method

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OPTICS EXPRESS 2018年第21期26卷 28080-28090页

作者： Wang, Qiang Yu, Siyuan Tan, Liying Ma, Sing Harbin Inst Technol Natl Key Lab Tunable Laser Technol Harbin 150001 Heilongjiang Peoples R China

In inter-satellite laser communication systems, accurate positioning of the beacon is essential for establishing a steady laser communication link. For inter-satellite optical communication, the main factor affecting the acquisition and tracking of the beacon is the background noise, such as stellar background light. In this study, we considered the effect of the background noise on a beacon in inter-satellite optical communication and proposed a new recognition algorithm for the beacon, which uses the optical flow vector obtained from the image data. We verified the feasibility of this method by performing simulation analysis and experiments. Both simulation and experiments showed that the new algorithm could accurately obtain the position of the centroid of the beacon under the effect of the background light. Furthermore, considering the identification probability of a light spot through the background light, the locating accuracy of the new algorithm was higher than that of the conventional gray centroid algorithm. Therefore, this new approach would be beneficial for the design of satellite-to-ground optical communication systems. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： image processing image processing algorithms Laser beams Laser communications Optical flow Systems design

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Speckle noise reduction in optical coherence tomography images based on edge-sensitive cGAN

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BIOMEDICAL OPTICS EXPRESS 2018年第11期9卷 5129-5146页

作者： Ma, Yuhui Chen, Xinjian Zhu, Weifang Cheng, Xuena Xiang, Dehui Shi, Fei Soochow Univ Sch Elect & Informat Engn Suzhou 215006 Peoples R China Soochow Univ State Key Lab Radiat Med & Protect Suzhou 215123 Peoples R China Minjiang Univ Collaborat Innovat Ctr IoT Technol & Intelligent Fuzhou 350108 Fujian Peoples R China

Speckle noise in optical coherence tomography (OCT) impairs both the visual quality and the performance of automatic analysis. Edge preservation is an important issue for speckle reduction. In this paper, we propose an end-to-end framework for simultaneous speckle reduction and contrast enhancement for retinal OCT images based on the conditional generative adversarial network (cGAN). The edge loss function is added to the final objective so that the model is sensitive to the edge-related details. We also propose a novel method for obtaining clean images for training from outputs of commercial OCT scanners. The results show that the overall denoising performance of the proposed method is better than other traditional methods and deep learning methods. The proposed model also has good generalization ability and is capable of despeckling different types of retinal OCT images. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： Anisotropic diffusion image analysis image processing algorithms image quality Speckle noise Speckle reduction

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Hybrid method for speckle noise reduction in digital holography

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS image SCIENCE AND VISION 2019年第12期36卷 D14-D22页

作者： Dong, Jun Jia, Shuhai Yu, Hongqiang Xi An Jiao Tong Univ Sch Mech Engn Dept Instrument Sci & Technol Xian 710049 Peoples R China

In digital holography, the inherited speckle noise degrades imaging quality due to the coherent laser source. To overcome this problem, a hybrid method for speckle noise reduction is presented by combining a novel angular diversity approach with the block-matching and 3D filtering (BM3D) algorithm. A serial of holograms is first captured by the proposed recording approach, and then the image with high signal-to-noise ratio is obtained by averaging multiple reconstructed intensity images. Finally, the residual noise in the averaged image is further eliminated by the BM3D filtering algorithm. The speckle noise is significantly suppressed, and a nearly speckle-free image can be obtained. Experimental results demonstrate the effectiveness of the proposed method. (c) 2019 Optical Society of America

关键词： Digital image processing image processing algorithms image quality Speckle noise Speckle patterns Speckle reduction

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Algorithm for detecting artificial objects against natural backgrounds

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JOURNAL OF OPTICAL TECHNOLOGY 2018年第6期85卷 338-342页

作者： Pronin, S., V Russian Acad Sci IP Pavlov Inst Physiol St Petersburg Russia

This paper describes an algorithm for distinguishing between images of two classes of objects: artificial and natural. An approximation to the image is generated using graphical elements similar to the receptor fields of neurons in the primary visual cortex (Zone VI). We show that the approximation-error distribution for natural-object images lies at higher values of the approximation error than that for artificial-object images. This difference makes it possible to detect artificial objects against natural backgrounds. (C) 2018 Optical Society of America

关键词： Bandpass filters image processing algorithms image recognition Nonlinear spatial filtering Spatial frequency Visual system

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AIKYATAN: mapping distal regulatory elements using convolutional learning on GPU

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BMC BIOINFORMATICS 2019年第1期20卷 488-488页

作者： Fang, Chih-Hao Theera-Ampornpunt, Nawanol Roth, Michael A. Grama, Ananth Chaterji, Somali Purdue Univ Dept Ag & Biol Engn W Lafayette IN 47907 USA Prince Songkla Univ Coll Comp Bangkok Thailand Google Inc Mountain View CA USA

Background: The epigenomics data deluge can leverage sophisticated ML techniques for functionally annotating the regulatory non-coding genome. The challenge lies in selecting the appropriate classifier for the specific functional annotation problem, within the bounds of the hardware constraints and the model's complexity. In our system Aikyatan, we annotate distal epigenomic regulatory sites, e.g., enhancers. Specifically, we develop a binary classifier that classifies genome sequences as distal regulatory regions or not, given their histone modifications' combinatorial signatures. This problem is challenging because the regulatory regions are distal to the genes, with diverse signatures across classes (e.g., enhancers and insulators) and even within each class (e.g., different enhancer sub-classes). Results We develop a suite of ML models, under the banner Aikyatan, including SVM models, random forest variants, and deep learning architectures, for distal regulatory element (DRE) detection. We demonstrate, with strong empirical evidence, deep learning approaches have a computational advantage. Plus, convolutional neural networks (CNN) provide the best-in-class accuracy, superior to the vanilla variant. With the human embryonic cell line H1, CNN achieves an accuracy of 97.9% and an order of magnitude lower runtime than the kernel SVM. Running on a GPU, the training time is sped up 21x and 30x (over CPU) for DNN and CNN, respectively. Finally, our CNN model enjoys superior prediction performance vis-'a-vis the competition. Specifically, Aikyatan-CNN achieved 40% higher validation rate versus CSIANN and the same accuracy as RFECS. Conclusions Our exhaustive experiments using an array of ML tools validate the need for a model that is not only expressive but can scale with increasing data volumes and diversity. In addition, a subset of these datasets have image-like properties and benefit from spatial pooling of features. Our Aikyatan suite leverages diverse epigenomic d

关键词： Support vector machines (SVM) Random forest (RF) Deep neural networks (DNN) ConvNets (CNN) image processing algorithms Distal regulatory elements Enhancers Silencers Epigenomics ROC curves Graphics processing units (GPU) Hyperparameter tuning NIH roadmap epigenomics

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Toward omnidirectional and automated imaging system for measuring oceanic whitecap coverage

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS image SCIENCE AND VISION 2018年第4期35卷 515-521页

作者： Al-Lashi, Raied S. Webster, Merlin Gunn, Steve R. Czerski, Helen Univ Leeds Fac Math & Phys Sci Sch Food Sci & Nutr Leeds W Yorkshire England Univ Southampton Fac Phys Sci & Engn Sch Elect & Comp Sci Southampton Hants England UCL Fac Engn Sci Dept Mech Engn London England

Accurate measurements of the oceanic whitecap coverage from whitecap images are required for better understanding the air - gas transfer and aerosol production processes. However, this is a challenging task because the whitecap patches are formed immediately after the wave breaks and are spread over a wide area. The main challenges in designing a whitecap-imaging instrument are the small field of view of the camera lens, processing large numbers of images, recording data over long time periods, and deployment difficulties in stormy conditions. This paper describes the design of a novel high-resolution optical instrument for imaging oceanic whitecaps and the automated algorithm processing the collected images. The instrument was successfully deployed in 2013 as part of the HiWINGS campaign in the North Atlantic Ocean. The instrument uses a fish-eye camera lens to image the whitecaps in wide angle of view (180 degrees).

关键词： Camera calibration image processing image processing algorithms image quality image resolution Imaging techniques

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Hyperspectral database of fruits and vegetables

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS image SCIENCE AND VISION 2018年第4期35卷 B256-B266页

作者： Ennis, Robert Schiller, Florian Toscani, Matteo Gegenfurtner, Karl R. Univ Giessen Dept Psychol Otto Behaghel Str 10 D-35394 Giessen Germany

We have built a hyperspectral database of 42 fruits and vegetables. Both the outside (skin) and inside of the objects were imaged. We used a Specim VNIR HS-CL-30-V8E-OEM mirror-scanning hyperspectral camera and took pictures at a spatial resolution of similar to 57 px/deg by 800 pixels at a wavelength resolution of similar to 1.12 nm. A stable, broadband illuminant was used. images and software are freely available on our webserver (http://***/GHIFVD;pronounced "gift"). We performed two kinds of analyses on these images. First, when comparing the insides and outsides of the objects, we observed that the insides were lighter than the skins, and that the hues of the insides and skins were significantly correlated (circular correlation = 0.638). Second, we compared the color distribution within each object to corresponding human color discrimination thresholds. We found a significant correlation (0.75) between the orientation of ellipses fit to the chromaticity distributions of our fruits and vegetables with the orientations of interpolated MacAdam discrimination ellipses. This indicates a close relationship between sensory processing and the characteristics of environmental objects. (c) 2018 Optical Society of America

关键词： Color spaces Color vision Hyperspectral imaging image processing algorithms Spectral imaging Visual system

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Multidispersed bubble-size measurements by interferometric particle imaging at scattering angles of 90° and 45°

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APPLIED OPTICS 2018年第36期57卷 10496-10504页

作者： Zhang, Hongxia Wang, Xiaolei Sun, Jinlu Jia, Dagong Liu, Tiegen Tianjin Univ Coll Precis Instrument & Optoelect Engn Tianjin 300072 Peoples R China Tianjin Univ Key Lab Optoelect Informat Technol Minist Educ Tianjin 300072 Peoples R China

Measurements of multidispersed bubble diameter are important in hydraulics, biology, and other such fields. Interferometric particle imaging (IPI) systems are used to measure the bubble diameter. In geometric approximation, the scattering angle cannot be greater than 2 arccos m. We propose a universal method for calculating the bubble diameter at wide scattering angles and use an IPI system to measure the bubble-size distribution at 90 degrees and 45 degrees. The particle size distributions measured at two angles are consistent with each other. The results of this study indicate that this method is suitable for measuring the bubble-size distribution. (C) 2018 Optical Society of America

关键词： Fourier transforms High power lasers image processing algorithms Particle scattering Scattering Spatial frequency

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Research on high-resolution imaging technology based on light field manipulation for a lenslet-based plenoptic camera

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APPLIED OPTICS 2018年第33期57卷 9877-9886页

作者： Liu, Xincheng Ma, Haotong Ren, Ge Qi, Bo Xie, Zongliang Chu, Junqiu Bai, Junjie Chinese Acad Sci Key Lab Opt Engn Chengdu 610209 Sichuan Peoples R China Chinese Acad Sci Inst Opt & Elect Chengdu 610209 Sichuan Peoples R China Univ Chinese Acad Sci Beijing 100039 Peoples R China

In this paper, an aberration correction method for an extended target is proposed to solve the problem of the lenslet-based plenoptic camera not imaging clearly under the influence of aberrations. We propose a light field manipulation method to improve performance of the light field imaging system. The principle of this method is that the sub-aperture images extracted from the raw light field image are offset when the light field imaging system is affected by aberrations, and the symmetrical arrangement of the sub-aperture image array is destroyed. By repairing the symmetrical arrangement of the sub-aperture image array, the influence of phase aberrations on the imaging system can be eliminated, and the resolution of the plenoptic camera can be improved. We use an image correlation algorithm to process the sub-aperture images of the plenoptic camera, calculate and compensate each sub-aperture image's displacement caused by aberrations, and restore the symmetrical arrangement of the sub-aperture image array;then, a corrected high-resolution refocused image can be generated. In particular, this method uses only the raw light field information obtained by the plenoptic camera in a single exposure, without adding other hardware devices. Furthermore, it takes the extended target itself as the reference image, so the ideal position need not be calibrated in advance. Also, the parallax information of the sub-aperture images is retained, and the method is simple and easy to use. Numerical simulation and experimental results show that the technology proposed in this paper can work well for high-resolution imaging of a plenoptic camera with phase aberrations. This method can be potentially applied to analyze lens aberration, media-induced image distortion such as water turbulence in underwater imaging, and atmospheric turbulence in remote imaging. It may have important application prospects in the fields of astronomical object detection, remote sensing, etc. (C) 2018 Optical

关键词： Atmospheric turbulence image metrics image processing algorithms Imaging systems Laser guide stars Underwater imaging

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