基于三帧差分和滑动平均背景的运动目标检测

针对传统三帧差分法在前景提取中容易出现“空洞”现象,对传统三帧差分法作改进,采用逻辑“或”代替原来的逻辑“与”,但同时产生了运动目标被拉长,轮廓模糊等问题。为了有效解决该问题,将滑动平均法和改进的三帧差分相结合,然而滑动平均法初始阶段更新背景较慢,因此二者有效结合的关键是对滑动平均法作改进,提出一种自适应更新滑动平均系数加速背景更新的方法。最后将改进三帧差分提取的前景和改进滑动平均法提取的前景进行逻辑“与”运算得到综合前景图像。实验结果表明该算法在完整性,准确性以及实时性方面能满足实际要求。     

基于对称差分和光流估计的红外弱小目标检测

针对复杂天空背景条件下低信噪比的红外弱小目标检测问题,提出了一种基于对称差分和光流估计相结合的目标检测算法。对序列红外图像做对称差分运算,通过图像差减运算和自适应阈值分割提取目标可能的运动区域,并对区域做扩张和叠加处理,得到连续帧间目标可能出现的区域。计算每个区域红外图像的光流场,对光流场进行阈值分割,辅以数学形态学滤波等方法,检测区域中的目标。该算法充分利用对称差分运算计算量小和光流检测准确度高的特点,在保证检测准确度的同时大大减少了目标检测算法的计算量。实验及结果分析表明,基于对称差分和光流估计的目标检测算法能实时有效地检测出复杂天空背景下的红外弱小目标。     

基于序列图像的运动目标检测

针对动态环境下运动目标检测中噪声多、目标检测不完整等情况,提出了一种基于金字塔多分辨率模型的运动目标检测方法,在低分辨率下获取目标的区域,在高分辨率下获取目标的细节。对于复杂的环境,还提出了运用高低双阈值替代传统的单阈值进行图像差分运算的方案,阈值可以根据图像自动分析得到。该方法首先将当前帧和背景帧进行尺度变换,得到不同分辨率下的图像组,然后在不同尺度下得到高低阈值差分图像,最后从高层向低层进行有效融合,得到噪声少的完整目标图像。实验表明,该方法提取运动目标的精度比较高,单目标达到0.802,多目标达到0.615,尤其是在复杂的动态环境下,优势比较明显。     

序列图像中运动目标的自动提取方法

针对目标检测与跟踪领域中的运动目标自动提取问题,提出了一种新的运动目标自动提取方法.利用已有的图像帧滤波后初始化背景,并在运动目标检测过程中,利用检测结果,不断地自动更新背景.使用背景差法检测运动区域,并对差分图像进行动态阈值分割,以及边缘链接,使其边缘处于基本连续状态.在得到的二值图上,提取轮廓,并根据目标大小选择面积阈值,剔除由于噪音或者背景提取不干净造成的虚假轮廓,将得到的轮廓掩模图像与原图像做逻辑与运算,提取出目标.实验结果表明,该方法可以有效地提取出刚体或非刚体运动目标.     

连续帧间差分与背景差分相融合的运动目标检测方法

为了克服背景差分法和帧间差分法的不足,有效提高运动目标检测的准确性、实时性和检测效率,提出了一种将连续帧间差分法与背景差分法相结合的运动目标检测方法.首先通过连续帧间差分法获得连续帧差图像,然后分别通过线性的自适应滤波、非线性的中值滤波获得背景图像进行差分,之后再利用阈值分割技术实现运动目标的增强,从而有效解决背景差分法和帧间差分法中都可能出现的无法检测目标的现象.实验表明,该算法可以有效避免漏检、误检等情况,提高运动目标检测的效率和准确性.     

水下运动目标实时检测算法研究

针对水下复杂环境情况,提出了一种快速实时检测水下运动目标的算法.在分析水下图像特性的基础上,对图像序列进行帧间差值运算得到差分图像,选择合适的阈值,对差分图像进行二值化和图像分割算法.结合差分图像中目标是由于待检测目标运动形成的特点,提出了衡量二值目标形状的线度指标的定义,可以描述目标的形状,从而实现快速实时检测水下运动目标.     

红外序列图像多运动目标检测

针对背景不动情况下提取红外图像运动目标,提出了一种基于连续四帧序列图像精确检测多运动目标的算法,并用软件仿真了该算法处理图像的效果并与其他方法进行了对比。经试验证明该方法算法简单,实时性好。对单目标、多目标、室内、室外、简单和复杂背景的红外序列都可以得到较好的检测效果。能够有效地去除背景和噪声,精确地确定运动目标位置,有利于后续的目标跟踪,算法适于实时应用。     

深空背景弱小目标实时检测算法研究

根据深空背景的特点,提出一种基于FPGA和DSP的检测算法,并设计相应的硬件系统,能对大小为512×512像素、帧频率为40帧/s的视频图像进行实时处理。先在FPGA中用最大中值滤波抑制空间成像噪声,解决了图像预处理运算量大对处理速度要求高的难题,再在DSP中用使用改进的双差分法进行运动目标分割,克服了单差分提取目标轮廓不准的缺点,最后结合候选目标的特征,采用基于逻辑的最近邻关联方法提取目标航迹。试验结果证明该算法满足了深空背景弱小目标实时检测的要求。     

复杂动背景下的“低小慢”目标检测技术

为了在复杂天空背景下检测出低空慢速小目标,本文研究了"低小慢"目标的视觉显著性区域特征,融合扫描线填充算法,提出了一种动态背景下"低小慢"目标自适应实时检测技术。首先,根据图像的亮度对比度获取显著性图。接着,使用形态学梯度提取显著性特征,通过三帧差分算法得到种子点。然后,使用扫描线填充算法进行生长,结合提出的自适应双高斯算法分割出前景。最后,根据候选目标的面积占比变化、质心距离变化、宽高比差异剔除虚假目标,完成检测。为了验证算法的有效性,本文选取了7组复杂天空背景的视频序列进行测试,并与其他优秀检测算法进行了对比。结果表明,本文提出的算法对运动目标检测的平均运行时间为0. 040 9 s,平均检测准确率为89. 97%,相比于其他算法的平均运算时间减少了0. 35 s,检测的平均准确率提高了24. 5%。算法在复杂背景下具有较好的稳定性和较强的鲁棒性。     

深空背景弱小运动目标检测算法研究

在深入分析监测设备CCD图像特点的基础上,提出了一种深空背景弱小运动目标检测新方法。该算法使用"列高通滤波器"进行背景抑制;采用序列图像多帧累加增强目标与恒星的对比度,用交叉投影法确定星点区域,提取局部星图,利用局部星图匹配剔除恒星干扰;结合候选目标的特征,采用基于逻辑的最近邻关联方法完成目标检测。结果表明,该算法可满足深空背景弱小运动目标实时检测的要求。     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.