Adaptive topology learning of camera network across non-overlapping views

An adaptive topology learning approach is proposed to learn the topology of a practical camera network in an unsupervised way. The nodes are modeled by the Gaussian mixture model. The connectivity between nodes is judged by their cross-correlation function, which is also used to calculate their transition time distribution. The mutual information of the connected node pair is employed for transition probability calculation. A false link eliminating approach is proposed, along with a topology updating strategy to improve the learned topology. A real monitoring system with five disjoint cameras is built for experiments. Comparative results with traditional methods show that the proposed method is more accurate in topology learning and is more robust to environmental changes.

Speckle structured illumination endoscopy with enhanced resolution at wide field of view and depth of field

Structured illumination microscopy(SIM)is one of the most widely applied wide field super resolution imaging techniques with high temporal resolution and low phototoxicity.The spatial resolution of SIM is typically limited to two times of the diffraction limit and the depth of field is small.In this work,we propose and experimentally demonstrate a low cost,easy to implement,novel technique called speckle structured illumination endoscopy(SSIE)to enhance the resolution of a wide field endoscope with large depth of field.Here,speckle patterns are used to excite objects on the sample which is then followed by a blind-SIM algorithm for super resolution image reconstruction.Our approach is insensitive to the 3D morphology of the specimen,or the deformation of illuminations used.It greatly simplifies the experimental setup as there are no calibration protocols and no stringent control of illumination patterns nor focusing optics.We demonstrate that the SSIE can enhance the resolution 2–4.5 times that of a standard white light endoscopic(WLE)system.The SSIE presents a unique route to super resolution in endoscopic imaging at wide field of view and depth of field,which might be beneficial to the practice of clinical endoscopy.

Integral imaging-based tabletop light field 3D display with large viewing angle

Light field 3D display technology is considered a revolutionary technology to address the critical visual fatigue issues in the existing 3D displays.Tabletop light field 3D display provides a brand-new display form that satisfies multi-user shared viewing and collaborative works,and it is poised to become a potential alternative to the traditional wall and portable display forms.However,a large radial viewing angle and correct radial perspective and parallax are still out of reach for most current tabletop light field 3D displays due to the limited amount of spatial information.To address the viewing angle and perspective issues,a novel integral imaging-based tabletop light field 3D display with a simple flat-panel structure is proposed and developed by applying a compound lens array,two spliced 8K liquid crystal display panels,and a light shaping diffuser screen.The compound lens array is designed to be composed of multiple three-piece compound lens units by employing a reverse design scheme,which greatly extends the radial viewing angle in the case of a limited amount of spatial information and balances other important 3D display parameters.The proposed display has a radial viewing angle of 68.7°in a large display size of 43.5 inches,which is larger than the conventional tabletop light field 3D displays.The radial perspective and parallax are correct,and high-resolution 3D images can be reproduced in large radial viewing positions.We envision that this proposed display opens up possibility for redefining the display forms of consumer electronics.

Impact of random and scattered coincidences from outside of field of view on positron emission tomography/computed tomography imaging with different reconstruction protocols

Image quality in positron emission tomography(PET)is affected by random and scattered coincidences and reconstruction protocols.In this study,we investigated the effects of scattered and random coincidences from outside the field of view(FOV)on PET image quality for different reconstruction protocols.Imaging was performed on the Discovery 690 PET/CT scanner,using experimental configurations including the NEMA phantom(a body phantom,with six spheres of different sizes)with a signal background ratio of 4:1.The NEMA phantom(phantom I)was scanned separately in a one-bed position.To simulate the effect of random and scatter coincidences from outside the FOV,six cylindrical phantoms with various diameters were added to the NEMA phantom(phantom II).The 18 emission datasets with mean intervals of 15 min were acquired(3 min/scan).The emission data were reconstructed using different techniques.The image quality parameters were evaluated by both phantoms.Variations in the signal-to-noise ratio(SNR)in a 28-mm(10-mm)sphere of phantom II were 37.9%(86.5%)for ordered-subset expectation maximization(OSEM-only),36.8%(81.5%)for point spread function(PSF),32.7%(80.7%)for time of flight(TOF),and 31.5%(77.8%)for OSEM+PSF+TOF,respectively,indicating that OSEM+PSF+TOF reconstruction had the lowest noise levels and lowest coefficient of variation(COV)values.Random and scatter coincidences from outside the FOV induced lower SNR,lower contrast,and higher COV values,indicating image deterioration and significantly impacting smaller sphere sizes.Amongst reconstruction protocols,OSEM+PSF+TOF and OSEM+PSF showed higher contrast values for sphere sizes of 22,28,and 37 mm and higher contrast recovery coefficient values for smaller sphere sizes of 10 and 13 mm.

A novel trigger algorithm for wide-field-of-view imaging atmospheric Cherenkov technique experiments

The high-altitude detection of astronomical radiation(HADAR)experiment is a new Cherenkov observation technique with a wide field of view(FoV),aimed at observing the prompt emissions ofγ-ray bursts(GRBs).The bottleneck for this type of experiment can be found in determining how to reject the high rate of nightsky background(NSB)noise from random stars.In this work,we propose a novel method for rejecting noise,which considers the spatial properties of GRBs and the temporal characteristics of Cherenkov radiation.In space coordinates,the map between the celestial sphere and the fired photomultiplier tubes(PMTs)on the telescope's camera can be expressed as f(δ(i,j))=δ'(i',j'),which means that a limited number of PMTs is selected from one direction.On the temporal scale,a 20-ns time window was selected based on the knowledge of Cherenkov radiation.This allowed integration of the NSB for a short time interval.Consequently,the angular resolution and effective area at 100 GeV in the HADAR experiment were obtained as 0.2°and 10^(4)m^(2),respectively.This method can be applied to all wide-FoV experiments.

Dynamic measurement of beam divergence angle of different fields of view of scanning lidar

The laser beam divergence angle is one of the important parameters to evaluate the quality of the laser beam.It can not only accurately indicate the nature of the beam divergence when the laser beam is transmitted over a long distance,but also objectively evaluate the performance of the laser system.At present,lidar has received a lot of attention as a core component of environment awareness technology.Micro-electromechanical system(MEMS)micromirror has become the first choice for three-dimensional imaging lidar because of its small size and fast scanning speed.However,due to the small size of the MEMS micromirror,the lidar scanning system has a small field of view(FOV).In order to achieve a wide range of scanning imaging,collimating optical system and wide-angle optical system are generally added to the system.However,due to the inherent properties of the optical lens,it is impossible to perfect the imaging,so the effects of collimating and expanding the beam will be different at different angles.This article aims to propose a measurement system that dynamically measures the divergence angles of MEMS scanning lidar beams in different fields of view to objectively evaluate the performances of scanning lidar systems.

Monte-Carlo simulation of pinhole collimator of a small field of view gamma camera for small animal imaging

Needs in scintimammography applications,especially for small animal cardiac imaging,lead to develop a small field of view,high spatial resolution gamma camera with a pinhole collimator.However the ideal pinhole collimator must keep a compromise between spatial resolution and sensitivity.In order to design a pinhole collimator with an optimized sensitivity and spatial resolution,the spatial resolution and the geometric sensitivity response as a function of the source to collimator distance has been obtained by means of Monte-Carlo simulation for a small field of view gamma camera with a pinhole collimator of various-hole diameters.The results show that the camera with pinhole of 1 mm,1.5 mm and 2 mm diameter has respectively spatial resolution of 1.5 mm,2.25 mm and 3 mm and geometric sensitivity of 0.016%,0.022%and 0.036%,while the source to collimator distance is 3 cm.We chose the pinhole collimator with hole diameter size of 1.2 mm for our the gamma camera designed based on the trade-off between sensitivity and resolution.

Flexible reduced field of view magnetic resonance imaging based on single-shot spatiotemporally encoded technique

In many ultrafast imaging applications, the reduced field-of-view（r FOV） technique is often used to enhance the spatial resolution and field inhomogeneity immunity of the images. The stationary-phase characteristic of the spatiotemporallyencoded（SPEN） method offers an inherent applicability to r FOV imaging. In this study, a flexible r FOV imaging method is presented and the superiority of the SPEN approach in r FOV imaging is demonstrated. The proposed method is validated with phantom and in vivo rat experiments, including cardiac imaging and contrast-enhanced perfusion imaging. For comparison, the echo planar imaging（EPI） experiments with orthogonal RF excitation are also performed. The results show that the signal-to-noise ratios of the images acquired by the proposed method can be higher than those obtained with the r FOV EPI. Moreover, the proposed method shows better performance in the cardiac imaging and perfusion imaging of rat kidney, and it can scan one or more regions of interest（ROIs） with high spatial resolution in a single shot. It might be a favorable solution to ultrafast imaging applications in cases with severe susceptibility heterogeneities, such as cardiac imaging and perfusion imaging. Furthermore, it might be promising in applications with separate ROIs, such as mammary and limb imaging.

Structured scene modeling using micro stereo vision system with large field of view

This paper presents a method for structured scene modeling using micro stereo vision system with large field of view. The proposed algorithm includes edge detection with Canny detector, line fitting with principle axis based approach, finding corresponding lines using feature based matching method, and 3D line depth computation.

Design of three-dimensional imaging lidar optical system for large field of view scanning

Three-dimensional(3D)lidar has been widely used in various fields.The MEMS scanning system is one of its most important components,while the limitation of scanning angle is the main obstacle to improve the demerit for its application in various fields.In this paper,a folded large field of view scanning optical system is proposed.The structure and parameters of the system are determined by theoretical derivation of ray tracing.The optical design software Zemax is used to design the system.After optimization,the final structure performs well in collimation and beam expansion.The results show that the scan angle can be expanded from±5°to±26.5°,and finally the parallel light scanning is realized.The spot diagram at a distance of 100 mm from the exit surface shows that the maximum radius of the spot is 0.506 mm with a uniformly distributed spot.The maximum radius of the spot at 100 m is 19 cm,and the diffusion angle is less than 2 mrad.The energy concentration in the spot range is greater than 90%with a high system energy concentration,and the parallelism is good.This design overcomes the shortcoming of the small mechanical scanning angle of the MEMS lidar,and has good performance in collimation and beam expansion.It provides a design method for large-scale application of MEMS lidar.

Calibration of Camera with Large Field-of-View Based on Flexible Planar Target

For high precision calibration of camera with large field-of-view,massive calibration points will be needed if traditional methods are selected,which makes the calibration complex and time-consuming.In order to solve this problem,a calibration method based on flexible planar target is proposed.In this method,distortion factor is firstly acquired by the invariance of cross ratio,and existing feature points are adjusted with the distortion factor.Then,a large number of points that will be used for the calibration are constructed with the adjusted feature points.Simultaneously,Tsai method is modified so as to reduce the complexity of calibration,which makes the process linear.The simulation and real experiments show that the method proposed in this paper is simple,linear,accurate and robust,and the precision of this method is close to that of Tsai method using abundant points.The method can satisfy the requirement of high precision calibration for camera with large field-of-view.

Study of a millimeter-wave squint indirect holographic algorithm suitable for imaging with large field-of-view

In this paper a millimeter-wave （MMW） squint indirect holographic method is presented, which is suitable for imaging with a large field-of-view. The proposed system employs the squint operation mode to remove the background and twin- image interferences, which achieves a similar effect to off-axis holography but leaves out the large-aperture quasi-optical component. The translational scanning manner enables a large field of view and ensures the image uniformity, which is difficult to realize in off-axis holography. In addition, a corresponding imaging algorithm for the presented scheme is developed to reconstruct the image from the recorded hologram. Some imaging results on typical objects, obtained with electromagnetic simulation, demonstrate good performance of the imaging scheme and validate the effectiveness of the image reconstruction algorithm.

基于LabVIEW的大视场激光视频图像采集系统

针对激光视频图像采集过程中视角不足、图像呈现效果不佳问题,设计基于LabVIEW的大视场激光视频图像采集系统。该系统利用帧触发器和串行接口与摄像机相连,控制摄像机拍摄大视场激光视频图像;摄像机依据IEEE-1394总线协议将拍摄的大视场激光视频图像,传输到视频图像编码器内,利用该编码器对其实施压缩编码处理后,将大视场激光视频图像传输到视频图像处理器内;该处理器采用LabVIEW软件编程形式,将视频图像处理算法程序写入其中,通过运行该程序对激光视频图像进行亮度差异调整、图像配准等处理,将处理后的图像存储到存储器内,并利用USB控制器连接显示屏,为用户程序大视场激光视频图像采集结果。实验表明:该系统的中断时间为2.0 min左右,采集的激光视频图像水平视场角由48°增加到83°,且压缩激光视频图像帧频率波动区间为33 f/s-34 f/s,系统具备较强的应用效果。

宽波段大视角液晶偏振转换器研究进展

偏振转换器能够通过对入射光偏振态的动态调控间接实现几何相位型多功能光学器件光学响应特性的动态可调。基于液晶的偏振转换器具有调控效率高、调控面积大、紧凑化程度高等诸多优势,是目前应用较为广泛的偏振转换器。本文围绕偏振转换效率、工作波段、视场角3个核心参量,系统介绍了液晶偏振转换器最新的研究进展,分别给出了典型液晶偏振转换器和大视角宽波段液晶偏振转换器的详细结构和性能表现,同时介绍了液晶偏振转换器工作波段和视角的拓展方法。该项工作能够为液晶偏振转换器结构设计与应用提供必要的参考,同时为基于几何相位或新型相位调控模式的研究提供一些思路。

大口径爆炸激波管出口冲击波流场图像测量

为了获取大视场下爆炸冲击波的纹影图像以及冲击波与被测模型相互作用后的流场演化特征,开展了基于聚焦纹影的反射式高速纹影测试。利用激光光源和高反射膜建立了系统所需的光源输入,并通过简化刀口栅设计,实现了远距离大口径爆炸激波管出口冲击波流场图像演化特征以及与固体模型相互作用的高时空分辨特征。研究结果表明,设计的聚焦式反射纹影系统在80 m以上距离处获取了大口径大当量爆炸激波管出口处6 m×3 m视场的冲击波特征,以及与固体相互作用的高时空分辨图像和状态数据;相比传统聚焦纹影系统,该系统具有结构简单、可实现性强、测试距离远,覆盖视场大等特点;通过设计不同光源输入,探讨了激光光源在远距离拍摄中的优势;通过冲击波阵面与固体模型的相互作用特征,揭示了冲击波作用于被测固体模型后的形成、演化和绕流状态。该测量结果能够为武器装备在受到冲击波作用后的状态评估和响应特性分析提供直观的图像数据支撑。

大视场白光干涉测量系统及性能研究

基于国产化的2倍迈克尔逊型干涉物镜组,优选配置0.5倍适配镜,对白光LED照明光源进行带通滤波参数的仿真估算和实验性能比较,构建了整套大视场白光干涉精密测量装置系统并进行了实验测试,通过白光干涉轴向响应实验曲线确定了中心波长。实验结果表明:通过光谱滤波获得了较为理想的白光干涉轴向响应曲线;系统的水平最大视场达到了14 mm;高度为2.04μm和20.43μm的标准台阶样品的测量结果分别为2.05μm和20.47μm,10次测量重复精度(标准差)分别为12 nm和16 nm。对粗糙度样板、微机电系统传感结构和半导体晶圆膜层进行了实测,表明所研制的系统装置在三维光学无损精密检测领域的应用具有可行性。

一种双视场电视/激光测距接收共光路一体化机设计

设计了一款双视场电视与激光测距接收共光路一体化机。根据应用需求,首先对CMOS、雪崩管器件选型;其次对光学、机械、电气部分进行设计,采用共用前物镜组,并利用镀有光谱分光膜的分光镜以及中继镜组,实现电视双视场与激光接收的共光路光学系统设计,电视大视场用于搜索目标,电视小视场用于跟踪目标,激光测距接收单元用于接收激光回波;然后采用主镜筒与整机壳体一体化设计,并以整体铸造方式进行加工,提高一体机整体结构强度;最后采用双H桥电机启动芯片并联设计,提高运行额定电流,并根据限位开关检测结果,实现电机对传动部件的精准限位控制。对设计结果进行分析,结果表明:设计的一体机大/小视场像质良好、像面稳定,激光测距接收单元工作状态良好。

多镜面大视场主动光学望远镜调控方法

为了更好地实现多镜面大视场主动光学望远镜波前像差抑制、提升望远镜探测能力极限,本文基于望远镜视场边缘内置的错位型曲率传感器进行波前感知,并利用功率谱对波前感知结果进行分析,进而基于波前像差的空间频率特征进行调控。首先,基于复光场理论分析了非瞳面对系统波前调控的影响机理。其次,分析了本方法在多镜面大视场主动光学望远镜调控过程中的精度特性。再次,利用桌面实验对多镜面大视场主动光学望远镜调控的可行性进行了验证。最终,波前重建结果与理论波前相关性高于0.85。利用功率谱对各个视场的空间频率特性进行了分析,与单纯使用均方根对多镜面影响敏感度进行分析的方法相比,灵敏度提升了20%。

基于全景图的城市街谷平均辐射温度计算模型研究

在评估城市街谷热环境对居民生活质量的影响时,明确街谷的微气候条件,尤其是平均辐射温度(Mean Radiant Temperature,MRT)对于改善城市热环境具有重要意义。现阶段,利用基于鱼眼图的天空视域因子(Sky View Factor,SVF)计算方法较为繁琐且难以实现大范围街谷MRT的时空分布评估。因此,本研究旨在通过全景图像技术,提出一种快速大量计算城市街谷MRT时空分布的新方法,并进一步考虑城市街谷中树木的影响,以改进传统模型。本研究首先基于全景图像批量获取城市街谷中的SVF,并结合城市街谷中的几何特征和植被视域因子,通过改进的平均辐射温度计算模型对单点的MRT进行计算,同时采用定点实测数据对该模型进行精确度验证,并将其应用于西安市街谷MRT的实际计算中。研究结果显示,经过模型验证,本研究方法具有较高的精度,相对误差大多数情况下在20%以内,RMSE在2.85~4.66℃。同时,模型与实测数据的一致性较好,能够清晰地反映MRT的变化趋势,R2大于0.74,IA大于0.80。与仅考虑单一不透水面的计算模型相比,考虑树木植被后的模型精度有明显提升,RMSE从5.15℃降至3.87℃,模型的R2由0.72提升至0.74,表明改进模型与观测结果具有更好的一致性。提出的基于全景图的MRT计算方法不仅提高了评估城市街谷热环境的效率和精度,而且通过考虑树木植被的影响,为城市规划和绿化管理提供了更加科学的指导。此外,本研究的方法和结论能够为城市热岛效应的缓解和城市生活环境的改善提供理论依据和技术支持。通过实例分析,研究成功地应用于西安市,展示了2021年7月14日上午9:00的街谷MRT分布图,为后续的城市热环境评估和改善工作奠定了基础。

有限视场下的攻击时间和角度多约束制导律

针对精确打击任务存在导引头视场受限这一过程约束的制导问题,提出了一种考虑视场限制以及攻击角度和时间多种约束的制导律.首先,在以比例导引项实现精确命中的基础上,利用最优控制理论,采用弹目距离加权控制能耗形式的指标函数,设计了攻击角度控制项,并推导了相应的剩余飞行时间解析预测表达式.其次,基于最优误差动力学方法,设计了攻击时间相关的控制项,保证了攻击时间误差的有限时间收敛.同时,针对导引头视场有限的问题,分析了各控制项对前置角收敛性的影响,利用特定的限制函数确保前置角在整个制导过程中始终处于有效视场内,并给出了前置角的有界性及收敛性证明.数学仿真结果验证了所提出制导律对多约束制导问题的有效性.