基于改进代价计算和自适应引导滤波的立体匹配

针对现有局部立体匹配算法在弱纹理区域匹配精度低的问题,提出一种基于改进代价计算和自适应引导滤波代价聚合的局部立体匹配算法。该算法首先将增强后的梯度信息与基于增强梯度的Census变换相结合,构建代价计算函数;然后对图像的每一个像素构建自适应形状十字交叉窗口,并基于自适应窗口进行引导滤波代价聚合;最后通过视差计算和多步视差精化得到最终的视差图。实验结果表明,改进后的算法在Middlebury测试平台上对标准立体图像对的平均误匹配率为4.80%,与基于传统引导滤波器的立体匹配算法相比,本文算法在弱纹理区域取得更好的匹配结果。     

一种改进Census变换与梯度融合的立体匹配算法

针对现有立体匹配算法对噪声敏感、易失真、在视差不连续区域与弱纹理区域误匹配率高的问题,提出一种改进Census变换与梯度融合的多尺度立体匹配算法。采用支持窗口内所有像素的加权平均灰度值作为Census变换的参考值,将Census代价与由水平和垂直方向归一化结合的梯度代价进行加权融合,通过设置噪声容限获得稳定的代价,提高了单像素匹配代价的可靠性;在多分辨率尺度下,采用改进引导滤波算法完成对匹配代价的聚合;通过视差提取获得视差图。实验结果表明,该算法在Middlebury测试平台上对标准立体图像对的平均误匹配率为4.74%,对27组扩展立体图像对的平均误匹配率为8.67%。该算法使得视差不连续区域与弱纹理区域的误匹配率进一步降低,且对噪声和光照等干扰表现出较好的稳健性。     

基于色彩权值和树形动态规划的立体匹配算

针对立体匹配算法在图像非遮挡区域,特别是弱纹理区域误匹配率较高的问题,提出一种基于十字交叉窗口下自适应色彩权值和树形动态规划的立体匹配算法。首先结合颜色、梯度信息及Census变换作为相似性测度函数构建代价计算函数;然后以图像的距离和色彩信息构建自适应十字交叉窗口,并提出基于色彩权值的代价聚集方式;将树形结构动态规划算法的思想引入到视差计算,代替单独采用赢者通吃策略的方法,对视差进行全局优化;最后通过视差求精得到稠密视差图。实验结果表明,本文算法在Middlebury测试平台4幅标准图像上非遮挡区域的平均误匹配率为2.45%,同时对其他10组图像进行了对比评估,本文算法有效地提高了图像非遮挡区域匹配的准确率。     

基于引导图像和自适应支持域的立体匹配

提出一种基于引导图像和自适应支持域的局部立体匹配算法。首先对校正后的输入图像进行预处理得到引导图像;在匹配代价计算阶段,提出一种梯度计算方法,结合引导图像和输入图像的梯度信息,分别计算x和y方向的梯度,再与AD(absolute difference)和Census变换融合构建匹配代价计算函数;在代价聚合阶段,使用基于自适应支持域的导向滤波;在视差细化阶段,提出一套基于自适应支持域的多步细化方法,通过该方法得到最终的视差图。实验结果表明,视差细化后全部区域的平均误差和方均根误差平均减少43.7%和38%,非遮挡区域平均减少33.7%和30.9%,所提算法具有较好的鲁棒性并能获得精度较高的视差结果。     

一种基于局域边缘特征的自适应立体匹配新算法研究

立体匹配,其目的是在对两幅存在一定视差的图像进行匹配后,获得两幅图像精确的视差图,是计算机视觉领域的重点和难点问题。为了快速、高效地获得高精度的稠密视差图,在充分研究了基于边缘特征的立体匹配和基于局部窗口的立体匹配两类算法的基础上,提出了一种基于局域边缘特征的自适应立体匹配算法。首先该算法自适应地选择局部匹配窗口大小,并计算其中相应位置的权值,实现初次匹配,然后再以基于边缘特征匹配获得的高精度稀疏视差图作为约束,修正部分误匹配点,最终获得准确、稠密的视差图。实验表明,该算法具良好的实验结果和较大的实用价值。     

基于像素类别优化的PatchMatch立体匹配算法

基于PatchMatch(同时估计像素点的视差和法向量的3D标签)的方案已经在立体匹配中取得高精度的亚像素视差,但该类方法无法有效解决图像无纹理区域的错误匹配。针对这一问题,对LocalExp(local expansion move)算法进行了改进,并提出一种融合多维信息的自适应像素类别优化的立体匹配算法。该方法设计了一种交叉窗口,在窗口内基于颜色与颜色的自相关信息构建相关权重,并利用约束函数剔除匹配代价中的离群值;在PatchMatch的标签初始化阶段增加约束机制,改进视差标签的建议生成机制,并利用基于局部扩张运动的优化方法求解标签值;利用基于像素类别的填充策略进行视差优化。实验结果表明所提算法能够在Middlebury数据集上取得较低的匹配误差。     

基于图像分割的稠密立体匹配算法

提出一种基于图像分割的稠密立体匹配算法,该算法将灰度-梯度算法与零均值归一化互相关(ZNCC)算法相结合生成匹配代价,利用SLIC(Simple Liner Iterative Cluster)算法对图像进行分割,基于视差图和超像素更新了匹配代价。在视差后处理阶段,基于左右一致性检验(LRC)、孔洞填充和十字交叉自适应窗口加权中值滤波的方法减小视差图的误匹配率。利用Middlebury数据集的4组图像进行测试,测试结果表明,平均误匹配率为4.99%。     

基于改进Census变换和异常值剔除的抗噪立体匹配算法

针对Census变换易受噪声影响使得立体匹配算法难以获取高匹配精度的问题,提出了一种改进Census变换和异常值剔除的抗噪立体匹配算法.在初始匹配代价阶段,该方法首先将窗口邻域中值作为参考值并通过映射函数控制异常值,提高了单像素匹配代价的可靠性;然后在代价聚合阶段,对动态聚合窗口中初始代价值进行异常值剔除;最后通过视差计算、视差优化得到最终的视差图.在VS2013软件平台上采用Middlebury标准测试图对初始匹配代价、代价聚合、最终视差图阶段进行测试.实验结果表明,本文算法的抗噪性能优于现有Census变换算法,且错误匹配率达到5.71%.     

基于水平树结构的可变权重代价聚合立体匹配算法

针对基于树结构的代价聚合方法中只利用颜色信息选择权值支持区域时,在图像边界区域易产生误匹配的问题,提出了一种基于水平树结构的可变权重代价聚合立体匹配算法。采用水平树代价聚合得到初始视差值,结合初始视差值与颜色信息重构水平树,在更新后的树结构上进行代价聚合,得到最终视差图。在视差后处理阶段,提出了一种改进的非局部视差后处理算法,将不满足左右一致性匹配的像素点引入匹配代价量构造中,提高了最终视差图的匹配精度。在Middlebury数据集的31对图像上进行测试,结果表明,未进行视差后处理时所提算法在未遮挡区域的平均误匹配率为6.96%,代价聚合平均耗时1.52s。     

基于改进Census变换和动态规划的立体匹配算法

为降低双目立体匹配算法在视差不连续区域和噪声干扰情况下的误匹配率,提出了一种基于改进Census变换和动态规划的立体匹配算法。采用支持区域为十字交叉形状窗口且设有噪声容限的改进Census变换进行代价计算,提高了单像素匹配代价的可靠性;利用引导图滤波器快速有效地完成代价聚合;在视差选择阶段,设计了一种改进的动态规划算法,消除了扫描线效应,提高了匹配速度和正确率;经过视差后处理得到最终视差图。实验结果表明,该算法在Middlebury测试平台上的平均误匹配率为5.31%,在低纹理区域和视差不连续区域均能得到准确的视差,运算复杂度低且具有较好的稳健性。     

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.