2021

• Record 337 of
  
  Title:Pixel-wise ordinal classification for salient object grading
  
  Author(s):Liu, Yanzhu(1); Wang, Yanan(2); Kong, Adams Wai Kin(1)
  Source: Image and Vision Computing  Volume: 106  Issue:   DOI: 10.1016/j.imavis.2020.104086  Published: February 2021  
  Abstract:Driven by business intelligence applications for rating attraction of products in shops, a new problem — salient object grading is studied in this paper. In computer vision, plenty of salient object detection approaches have been proposed, while most existing studies detect objects in a binary manner: salient or not. This paper focuses on a new problem setting that requires detecting all salient objects and categorizing them into different salient levels. Based on that, a pixel-wise ordinal classification method is proposed. It consists of a multi-resolution saliency detector which detects and segments objects, an ordinal classifier which grades pixels into different salient levels, and a binary saliency enhancer which sharpens the difference between non-saliency and all other salient levels. Two new image datasets with salient level labels are constructed. Experimental results demonstrate that, on the one hand, the proposed method provides effective salient level predictions and on the other hand, offers very comparable performance with state-of-the-art salient object detection methods in the traditional problem setting. © 2020 Elsevier B.V.
  Accession Number: 20210109710833
• Record 338 of
  
  Title:Design analysis and test verification of a rigid-flexible, dual-mode coupling support structure for space-based rectangular curved prisms
  
  Author(s):Jia, Xin-Yin(1,2); Wang, Fei-Cheng(1); Li, Li-Bo(1); Zhang, Zhao-Hui(1); Liu, Jia(1); Hu, Bing-Liang(1)
  Source: Applied Optics  Volume: 60  Issue: 25  DOI: 10.1364/AO.431394  Published: September 1, 2021  
  Abstract:In view of the functional requirements of high reliability and stability support of optical components of space remote sensors, a rigid-flexible, dual-mode coupling support structure for space-based rectangular curved prisms (SRCPs) was designed. In-depth studies of the support principle and engineering realization of theSRCPs and optimization of the flexible adhesive structure were performed. Static and dynamic simulations were conducted on the mirror subassembly by means of finite element analysis, and test verification was also performed. The tests revealed that the surface shape error of the mirror subassembly after mechanical testing was 0.021λ, the displacement of the mirror body was 0.008 mm, the inclination angle was∼0.8'', the mass of the mirror subassembly was 4.79 kg, the fundamental frequency was 283 Hz, and the maximum amplification of the total rms acceleration was 4.37. All indexes were superior to those of the design requirements. On this basis, bonding tests and mechanical tests of a rectangular curved prism reflector, a rectangular curved prism, and a rectangular plane reflector employing this proposed support structure were continued. The test results verified the reliability, stability, and universal applicability of the proposed rigid-flexible, dual-mode peripheral bonding support structure. © 2021 Optical Society of America.
  Accession Number: 20213510838944
• Record 339 of
  
  Title:Effect of pupil matching of cold shield on the fringe contrast of long-wave infrared spatial heterodyne spectroscopy
  
  Author(s):Han, Bin(1,2); Feng, Yutao(1); Zhang, Zhaohui(1); Wu, Junqiang(1); Wu, Yang(1,2); Sun, Jian(1); Wang, Pengchong(1); Chang, Chenguang(1); Li, Juan(1); Zhao, Yudi(1); Hu, Bingliang(1)
  Source: Applied Optics  Volume: 60  Issue: 29  DOI: 10.1364/AO.439482  Published: October 10, 2021  
  Abstract:Matching the cold shield with the exit pupil of the fringe-imaging system of long-wave infrared (LWIR) spatial heterodyne spectroscopy (SHS) damages illumination uniformity of the interferogram and affects the fringe contrast, which is a significant parameter for LWIR SHS. The optical models of the fringe-imaging system considering and not considering the pupil matching of the cold shield are built to illustrate the effect on the fringe contrast. Simulations based on the optical design software ASAP are conducted to verify the fringe contrast loss for field-widened LWIR SHS. The result shows that the pupil matching of the cold shield decreases the fringe contrast of LWIR SHS and field-widened LWIR SHS by 0.049% and 0.053%, respectively, and the fringe contrast loss increases with the degree of deviation from the telecentric condition of the fringe-imaging system. © 2021 Optical Society of America.
  Accession Number: 20214111005981
• Record 340 of
  
  Title:Laser-induced fluorescence and its effect on the damage resistance of fluoride-containing phosphate-based glasses
  
  Author(s):Li, Shengwu(1,2); Yang, Yanqiang(3); Song, Yunfei(3); Wan, Rui(1,2); Ma, Yuan(1,2); Peng, Bo(1,2); Zhang, Guangwei(4); Wang, Pengfei(1,2)
  Source: Ceramics International  Volume: 47  Issue: 9  DOI: 10.1016/j.ceramint.2021.01.181  Published: May 1, 2021  
  Abstract:A series of multi-component fluoride-containing phosphate-based glasses prepared in a reducing atmosphere showed improved resistance to high-energy ultraviolet (UV) laser-induced damage and strong laser-induced fluorescence (LIF) within the glass bulk. The UV optical absorption, photoluminescence, and fluorescence decay properties of these glasses were investigated to explore the defect-related LIF mechanism and its underlying effect on the glasses’ laser-induced damage threshold (LIDT). Seven laser wavelengths ranging from 253 nm to 532 nm were used to excite the LIF, and two characteristic fluorescence bands peaking at approximately 414 nm and 780–800 nm occurred in all three types of glasses. The LIF band at 414 nm was attributed to PO3-EC defects in the second harmonic frequency (2ω) absorptive glass and third harmonic frequency (3ω) transparent glass, but Fe2+ ions in the fundamental frequency (1ω) absorptive glass. A later fluorescence band at 780–800 nm occurred due to POHC defects in the 2ω absorptive and 3ω transparent glasses and Fe3+ ions in the 1ω absorptive glass. A detailed study on the dynamic decay processes of two additional dominant fluorescence peaks at 450 nm and 780 nm under 266 nm excitation revealed the potential effect of LIF on LIDT improvement. The relatively longer LIF lifetime, higher LIF intensity, and larger LIF peak area corresponded with and contributed to a higher LIDT, especially in the 3ω transparent glass with a low UV absorption coefficient. This study provides strong evidence for the prior hypothesis between strong LIF and LIDT. © 2021 Elsevier Ltd and Techna Group S.r.l.
  Accession Number: 20210509855597
• Record 341 of
  
  Title:Calibration Method for Structural Parameters and Assembly Error of Light Field Camera
  
  Author(s):Yuan, Suochao(1,2); Li, Ming(1,2); Da, Zhengshang(1)
  Source: Zhongguo Jiguang/Chinese Journal of Lasers  Volume: 48  Issue: 20  DOI: 10.3788/CJL202148.2004001  Published: October 25, 2021  
  Abstract:Objective: A light field camera that is capable of capturing four-dimensional light field information through a single shot can be realized by inserting a microlens array in front of the sensor of a traditional camera. It has great potential to play important roles in many applications such as 3D measurement, flow field velocimetry, and wavefront sensing. To obtain the image information, the captured light-field information shall be decoded. The decoding process is largely based on the structural parameters of the light field camera, including the distance between the microlens array and sensor and the pitch of the microlens array. Because of the errors introduced during the manufacturing and assembling processes, using the nominal values of these parameters are not recommended; calibration of the true values and assembly errors are desired. Several studies have been conducted on the calibration of light field cameras. However, most of these studies follow the framework of the calibration method used for traditional cameras, where a complicated imaging model is built and the unknown parameters are searched using an optimization algorithm. The complexity of procedures in such methods makes them difficult to implement. Based on optical test principles, a new calibration method using simpler calibration models is proposed, which enables fast calibration. Methods: The proposed calibration method comprises two parts: calibration with the main lens and calibration without the main lens. The calibrations of structural parameters are accomplished when the main lens is mounted, and the calibration model is based on the relation that the exit pupil of the main lens is imaged by the microlens. A uniform light source is used to illuminate the pupil of the main lens to obtain calibration images. The distance between the microlens array and sensor and the pitch of the microlens array are treated as two optimized variables of an optimization model and are calculated by searching the optimal values. The calibration of assembly errors is accomplished when the main lens is removed, and the calibration model is based on the imaging feature of the microlens for object points at infinity. A collimated beam is used to illuminate the microlens array to obtain calibration images. Rotation and tilt errors are obtained by analyzing the geometry of the spot array in calibration images. Results and Discussions A self-constructed light field camera is calibrated using the proposed method. The distance between the microlens array and sensor, for which the nominal value is 2.1300 mm, is calibrated to be 2.2738 mm. The pitch of the microlens array, for which the nominal value is 0.3000 mm, is calibrated to be 0.3001 mm. Furthermore, the distance between the microlens array and exit pupil of the main lens is calculated to be 47.7058 mm (Table 1). The rotation error between the microlens array and sensor is calibrated to be 0.1785°, which shall be corrected according to formula (2), and the pitch of microlens array is calculated to be 0.3001 mm by extracting the distance between adjacent spot centroids on the calibration image. The tilt error between the microlens array and sensor is 0.0083° and 0.0047° along the row and column directions of the sensor, respectively, and the distance between the microlens array and sensor is calculated to be 2.2719 mm based on equation (11). The relative deviation of the calibration values of the distance between the microlens array and sensor obtained from the two different methods is 0.84%. Based on the calibration data, reconstruction of the light field is executed and the rotation error is corrected. Compared with the reconstructed images before calibration, the quality of reconstructed images after calibration improved (Fig.10). Conclusions: To solve the problem of calibration of structural parameters and assembly errors of light field cameras, a calibration method based on optical test principles is proposed. A uniform light source is used to illuminate the optical pupil of the main lens, and the array of images of the optical pupil on the sensor is used for calculating the structural parameters, including the pitch of the microlens array and the distance between the microlens array and sensor. The assembly errors can be calibrated with the main lens removed and the microlens array illuminated directly by a collimated light beam. The calibration images captured for assembly error calibration can also be used for estimating the structural parameters through simple geometric analysis, which can serve as comparisons for the calibration results obtained from the method with the main lens mounted. Experiment results show that the calibrated and nominal values of structural parameters agree well with each other, indicating that the proposed calibration method is feasible. © 2021, Chinese Lasers Press. All right reserved.
  Accession Number: 20214711193946
• Record 342 of
  
  Title:Tilt error correction of minitype theodolite's vertical shaft based on angular contact ball bearings
  
  Author(s):Li, Xiangyu(1,2); Peng, Bo(1,2); Jiang, Bo(1); Ruan, Ping(1)
  Source: Hongwai yu Jiguang Gongcheng/Infrared and Laser Engineering  Volume: 50  Issue: 12  DOI: 10.3788/IRLA20210172  Published: December 25, 2021  
  Abstract:The design of minitype theodolite's vertical shaft which based on angular contact ball bearings usually refer to similar model for estimation and analogy. This method can effectively improve the design efficiency as well as endowing the vertical shaft a better engineering practicability. However, these experience-based designs hardly reach the best options, hence leaves room for optimizing and improvements. The vertical shaft of a small theodolite was studied from tilt error correction. The shaft optimization parameters were determined based on the physical model. Then the design parameters of bearing outer end ring were optimized by using finite element analysis. At the same time, the selection of bearing fit clearance's design parameter values were analyzed through tilt error theoretical modeling. Meanwhile, the biaxial perpendicularity errors of this small theodolite with and without optimizing were both detected after partial load hoisting. The result shows that the biaxial perpendicularity error of optimized theodolite is lower with an approximate value of 6", compared unoptimized theodolite with an approximate value of 20". Tilt error of the rear vertical shaft is less than that before optimizing. The rationality and effectiveness of this optimization method mentioned are verified. Copyright ©2021 Infrared and Laser Engineering. All rights reserved.
  Accession Number: 20220211449112
• Record 343 of
  
  Title:Surface response correction method of light intensity detector in high energy laser measurement
  
  Author(s):Xue, Fang(1,2); Chen, Yongquan(1); Duan, Yaxuan(1); Lin, Hui(1); Da, Zhengshang(1)
  Source: Hongwai yu Jiguang Gongcheng/Infrared and Laser Engineering  Volume: 50  Issue:   DOI: 10.3788/IRLA20210215  Published: October 25, 2021  
  Abstract:In order to reduce the influence of the non-uniformity of the surface response of the intensity detector on the near field parameter measurement for the high-energy laser inertial confinement fusion device (ICF), a correction method for the non-uniformity of the light-intensity detector surface response in the near-field parameter measurement of the high-energy laser was proposed. Theoretically, a multi-point calibration linear correction model based on the high-energy laser near-field spatial evaluation factor was deduced, and a non-uniformity automatic correction device on surface response for high-uniformity linear output light intensity detector was designed and built. In order to verify the effectiveness of the proposed method, the surface response non-uniformity of a certain type of scientific-grade CCD was corrected. The surface response modulation degree of the detector was reduced from 1.42 to 1.08, and the contrast was reduced from 0.014 to 0.004. Compared with the two-point calibration method, the uniformity of the light intensity detector after correction using the proposed method in this article was greatly improved. The results show that this method can provide an effective technical means for the correction of the uniformity of the surface response of the light intensity detector in the parameter measurement of the high-energy laser ICF device in my country. © 2021, Editorial Board of Journal of Infrared and Laser Engineering. All right reserved.
  Accession Number: 20214511111286
• Record 344 of
  
  Title:A Pose Measurement Algorithm of Space Target Based on Monocular Vision and Accuracy Analysis
  
  Author(s):Dong, Yongying(1); Zhang, Gaopeng(2); Chang, Sansan(2); Zhang, Zhi(2); Li, Yanjie(3)
  Source: Guangzi Xuebao/Acta Photonica Sinica  Volume: 50  Issue: 11  DOI: 10.3788/gzxb20215011.1112003  Published: November 25, 2021  
  Abstract:Aiming at the low efficiency of traditional orthogonal iterative algorithm, an improved orthogonal iterative algorithm is proposed to measure the pose of space objects based on monocular vision. Firstly, based on the traditional orthogonal iterative algorithm, the translation vector in the iterative process was eliminated. The initial value of the rotation matrix was solved by using the parallel perspective model instead of the weak perspective projection model, so as to accelerate the solution process of the orthogonal iterative algorithm. Secondly, simulation experiments are used to study the effects of the extraction accuracy of the imaging point, the accuracy of three-dimensional coordinate of the space feature point, the calibration accuracy of the camera principal point, the calibration accuracy of the camera focal length and the number of space feature points on the accuracy and efficiency of the algorithm. Based on the results of the simulation experiments, Taguchi method is used to quantitatively analyze the influence of each factor on the accuracy of the algorithm, and find out the factor that has the greatest influence on the accuracy of the improved orthogonal iteration algorithm. Finally, the performance of the proposed improved orthogonal iteration algorithm is tested by the physical experiments. The physical experiments prove that the proposed method is accurate, and takes shorter run time than that of traditional orthogonal iteration algorithm. Based on the results of the orthogonal experiment, the accuracy of the improved orthogonal iteration algorithm could meet different demand of different space task by controlling the different influence factors. © 2021, Science Press. All right reserved.
  Accession Number: 20215011322023
• Record 345 of
  
  Title:SAHS detection using contact-free MZI-BCG sensor
  
  Author(s):Jiang, Xinning(1); Xu, Wei(2,3); Yu, Cheung Chuen(4); Sun, Wenye(5); Dong, Bo(6); Yu, Changyuan(7,8); Zhao, Wei(2,3,9); Wang, Yishan(2,3,9)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 11894  Issue:   DOI: 10.1117/12.2601391  Published: 2021  
  Abstract:Real-Time SAHS events detection system during sleep is proposed and investigated based on contact-free Mach-Zehnder Interferometer ballistocardiograph (MZI-BCG) senor, which is placed under the mattress. The breath activity influences the optical phase difference of the MZI which is demodulated with 3∗3 optical coupler. In this paper, three SAHS events are successfully detected, including OSAS (Obstructive sleep apnea syndrome), CSAS (Central sleep apnea syndrome) and MSAS (Mixed sleep apnea syndrome). The proposed system is simple, cost-effective and non-invasive, which has great potential application in home monitoring © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
  Accession Number: 20215211394018
• Record 346 of
  
  Title:Semi-supervised LDA Based Method for Similarity Distance Metric Learning
  
  Author(s):Deng, Ren(1); Chen, Yaxuan(2); Han, Ruilin(1); Xiao, Han(1); Li, Xijie(3)
  Source: ACM International Conference Proceeding Series  Volume:   Issue:   DOI: 10.1145/3459955.3460606  Published: March 17, 2021  
  Abstract:In recent years, computer vision technology has drawn much attention of people and been applied into many fields of human's living. Data classification/identification is a key task in computer vision. The similarity distance metric learning based method is wildly used to compare the similar positive pairs from dissimilar negative pairs. However, there are more and more challenging computer vision task have been proposed. Traditional similarity distance metric learning methods are fail to metric the similarity of these task due to the drastic variation of feature caused by illumination, view angle, pose and background changes. Thus, the existing methods are unable to learn effective and complete patterns to describe the appearance change of individuals. To overcome this problem, we proposed a novel semi-supervised (Linear Discriminant Analysis) LDA based method for similarity distance metric learning. The proposed method first learn a metric projection with traditional LDA method. The then test data are identified with the potential positive pairs to fine-turning the metric model by forcing the identified data to be close to the center of positive training data pairs. Finally, the proposed method are compared to some classic metric learning algorithms to demonstrate its effectiveness and accuracy. © 2021 ACM.
  Accession Number: 20213310759591
• Record 347 of
  
  Title:Pneumonia image classification based on convolutional neural network
  
  Author(s):Xiong, Feng(1); He, Di(1); Liu, Yujie(1); Qi, Meijie(1); Zhang, Zhoufeng(2); Liu, Lixin(1,2)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 12057  Issue:   DOI: 10.1117/12.2606413  Published: 2021  
  Abstract:Chest X-ray is the commonly used method to diagnose pneumonia. How to correctly interpret the image information is always the main challenge faced by doctors. Convolution Neural Network (CNN) is a popular deep learning algorithm with excellent image recognition performance, and has been used widely in automatic recognition and diagnosis of medical images. This paper studies the classification of normal and pneumonia with more than 5000 chest X-ray images by employing three CNN models of VGG16, VGG19 and Inception V3. The performances of each model for classification was evaluated and compared. © 2021 COPYRIGHT SPIE.
  Accession Number: 20215211375378
• Record 348 of
  
  Title:Influence of spectral characteristics of light sources on measuring space camera modulation transfer function
  
  Author(s):Liu, Shang-Kuo(1,2); Wang, Tao(1); Li, Kun(1); Cao, Kun(1); Zhang, Xi-Bin(1); Zhou, Yan(1); Zhao, Jian-Ke(1); Yao, Bao-Li(1)
  Source: Wuli Xuebao/Acta Physica Sinica  Volume: 70  Issue: 13  DOI: 10.7498/aps.70.20201575  Published: July 5, 2021  
  Abstract:Modulation transfer function (MTF) measurement is a major means to evaluate the imaging quality of a space camera. The influence caused by the spectral characteristic of light source on the MTF results is not negligible, because the transmittance and color aberration of optical systems, and quantum efficiency of the space camera detectors are all spectrally related. Thus, MTF results tested by different light sources are different from each other. To address this problem, we propose a method to analyze the influence of spectral characteristics of light sources on measuring the MTF of space cameras. In addition, the devices and methods are designed to calibrate the spectral response and monochrome point spread function (PSF) of space camera. A Sigma lens (focal length: 1000mm, F number: 5.6) and a Cannon EOS 5DSR camera (pixel size: 4.14 μm) are combined into an experimental space camera, whose spectral response is calibrated with a monochromator (Omno30300, NBeT) and a spectral radiometer (FieldSpec, ASD). We calibrate the monochrome PSF of the Sigma lens with the same monochromator and a CCD (PIXIS 1024, Princeton Instruments, pixel size: 13 μm) micro-measuring system (20X objective). During the calibration of spectral response and monochrome PSF, the same collimator (focus: 5000 mm, F number: 10) is used. With using the proposed method and those calibrating data, we compute the theoretical values of the MTF of a space camera measured separately with five different light sources. The results indicate that MTF measured by a xenon lamp is greatly different from those MTFs measured by the other four light sources. Comparisons of those theoretically calculated MTFs, separately, show that the MTF measured by a tungsten halogen lamp is greater than the MTF measured by a xenon lamp at each spatial frequency. The deviation between those two lamps reaches a maximum value of 0.075 in the medium-high frequency zone. Furthermore, in order to verify those theoretical conclusions, a platform including a collimator and the previous space camera is constructed. The MTFs measured by a tungsten halogen lamp and a xenon lamp are computed with the slanted-edge method respectively. The results demonstrate that the distributions and deviations of the MTFs tested by those two lamps are identical to those theoretical results at each spatial frequency, with the maximum deviation being 0.057. The theoretical and experimental results demonstrate that the suggested method can accurately calculate the influence of spectral characteristics of light sources on measuring MTF of space cameras. The proposed method can also be adopted to investigate the influence of spectral characteristics of light sources on MTF of optical systems in the design or test stages. © 2021 Chinese Physical Society.
  Accession Number: 20213410814836