基于遗传算法选择多光源下的光谱反射率重构研究

为解决基于RGB三通道信息值重构光谱反射率精度不理想的问题,提出了一种优化的基于RGB三通道信息的光谱反射率重构算法。首先编码产生随机选择多个光源的个体,RGB三通道值通过多项式回归算法预测多个光源下的三刺激值,并采用伪逆法进行多光源下的光谱反射率重构,然后将样本的重构精度作为个体的适应度评估值,以优胜劣汰,适者生存为原则对个体进行选择、交叉、变异操作,最后得到适用于颜色样本光谱重构的多个光源与基于这些光源重构得到的光谱反射率。实验选用Munsell颜色集作为训练样本集,RC24色卡、SG140色卡作为检测样本集,8个标准光源和82个发光二极管光源作为实验光源,采用该算法从90个光源中选取最优的光源组合并重构得到样本的光谱数据,并与Zhang提出的基于穷举法选择的多光源下的光谱重构方法和A光源下的伪逆法进行了重构精度对比。实验结果显示该研究提出的方法随着光源个数的增加,光谱反射率重构精度提高,特别是光源个数增加到3时,光谱重构精度提高的幅度最大。在三种重构方法中,该方法重构RC24的平均色差和平均光谱均方根误差分别为0.332 4和0.002 9,而Zhang的方法与伪逆法的平均色差分别为0.429 3和3.266,平均光谱均方根误差分别为0.029 7和0.004 8;该文方法重构SG140的平均色差和平均光谱均方根误差分别为0.486 2和0.007 3,而Zhang的方法与伪逆法的平均色差分别为0.544 8和3.821 9,平均光谱均方根误差分别为0.035 6和0.013 3。结果表明基于多光源下的光谱反射率重构精度明显优于基于单个光源下的重构精度,而基于遗传算法的多光源选择方法又优于穷举法,它能够根据颜色样本自动寻找到最优光源组合,从而基于最优多光源下的三刺激值重构样本的光谱反射率,提高了光谱反射率重构的精度。     

Recovery of reflectance spectra from colorimetric data using principal component analysis embedded regression technique

The classical principal component analysis technique is enhanced for reconstruction of reflectance spectra of surface colors from the corresponding tristimulus values under a given set of viewing conditions, i.e., D65 illuminant and 1964 standard observer. In this paper, the number of implemented eigenvectors has been virtually extended from three to six by estimation of another set of tristimulus values under illuminant A and 1964 standard observer. The second set of colorimetric data was predicted by the conventional non-linear regression method and used in the spectral reconstruction to produce a fully determined system in the case of six eigenvectors. The improvement obtained from the proposed modification was examined for the recovery of the reflectance spectra of Munsell color chips as well as ColorChecker DC samples. The performance is evaluated by the mean, maximum and standard deviation of color difference values under other sets of light sources. The values of mean, maximum and standard deviation of root mean square (RMS) errors between the reproduced and the actual spectra were also calculated. Results are compared with those obtained from traditional methods using the principal component analysis (PCA) routine. All metrics show that the suggested method leads to considerable improvements in comparison with the standard PCA approach.     

基于相机rawRGB通过加权多项式和维纳估计方法重建光谱反射率

基于相机RGB预测物体光谱反射率的研究一直备受研究者们的关注。传统方法都是通过单一光源下的信息进行光谱反射率恢复。最近,Zhang等在Color Research & Application报道了一种基于单光源相机RGB信息预测物体光谱反射率的两步方法。首先基于单个光源下的相机响应RGB值,挑选出一定量的训练数据,采用多项式模型和伪逆的方法预测出不同光源下的CIE XYZ值;然后根据预测的多光源下的CIE XYZ值及整体训练数据预估光谱反射率,再通过预估的光谱反射率挑选一定量训练样本,通过伪逆方法预测出物体光谱反射率。尽管仍然基于一个光源下的相机响应RGB,但通过映射到多光源下的色度值XYZ,提高输入信息的维度来优化光谱反射率的重建精度。受Zhang等工作的启发,提出新的基于单一光源下相机的raw RGB响应信息,通过三阶多项式模型扩展的加权最小二乘方法对多光源下的CIE XYZ值进行预测,然后根据预测出的多光源下的CIE XYZ值再通过维纳估计的方法进行光谱反射率重建,通过这样的两步方法实现从相机响应RGB到光谱反射率的重构。该新方法,采用全体训练数据,应用十分方便,避免了Zhang等的方法需要挑选一定量的局部训练样本的问题。同时Zhang等的方法挑选出的局部训练样本同等重要,而该方法在第1步中,根据训练样本与给定的测试样本的接近程度,赋予训练样本不同的权重,以提高预测精度。通过采用140色色卡作为训练样本,24色色卡和自制的44色印刷品样本进行测试,以判断预测和实测反射率接近程度的均方根误差（RMSE）和人感知色差为评价标准进行比较,结果表明,该方法明显优于Zhang等的方法,而且预测精度随着光源数量的增加而提高,当光源个数达到6时,表现最佳。     

采集舌象用光源的光谱研究

在中医舌诊中,传统的光源通常为自然光甚至烛光,易受气候,环境干扰,不利于医生获得正确的舌苔色泽信息。文章引进人造光源作为对自然光源的补充或直接应用人造光源来代替自然光,能得到稳定和真实的舌态图像,获得科学严谨的诊断结果。不同的光源由于其各异的辐射光谱功率分布,显色性Ra和色温Tc的不同对同一物体照明会产生不同的颜色。文章选择了四种人造光源,通过光谱分析和分别照明时拍摄的相同图像[1]、舌象,用舌象视觉计算比较的方法选出了最佳光谱对应的光源,并在多个光学参数,色坐标容差椭圆等色度学参数上进行比较,得出一种最接近于自然光的光源,即PHILIPS YPZ220/18-3U.RR.D型光源,其色温为6 500 K的光谱特性及光学参数最接近自然光源,可作为采集舌象时的照明标准光源。此方法可为选择人造标准光源替代自然日光提供理论和实验依据。     

基于凸组合核函数的化合物太赫兹透射光谱分类

物质的太赫兹光谱包含着非常丰富的物理和化学信息。它对化合物晶体具有高的灵敏度、 单光子能量低等特点。但受到检测人员知识背景、 背景噪声、 识别算法精度等因素的影响,光谱样本识别准确率和效率较低。为了提高对太赫兹光谱的检测能力,提出应用基于凸组合核函数的support vector machines(SVM)对化合物的THz脉冲透射谱进行分类。在使用小波变换对数据进行滤波预处理之后,提取了传统波峰、 波谷位置特征和term frequency-inverse document frequency (TF-IDF) 最大间隔特征。TF-IDF方法使用信息论的原理确定每个采样点的权重,选择权重较大的点作为特征。针对太赫兹透射谱特征相似、 维数较低带来的分类困难问题,构建基于凸组合核函数的SVM分类模型。并利用核评价的方法,通过高维非线性规划方程求解最优凸组合参数。当最优凸组合参数被确定时,构建分类模型进行分类和预测。相比较于单一核函数,凸组合核函数将透射谱特征与分类模型融合起来。对于不同的检测样本,数据经过凸组合核函数映射到高维空间后,特征具有更显著的区分度。使用不同的太赫兹透射谱样本进行分类实验,结果表明,分类准确率得到极大提高。     

光源光谱对标志逆反射系数的影响

以光源发射光谱和逆反射材料光谱反射率曲线为基础,通过数据拟合的方式研究了多种光源照射条件下材料逆反射系数的相对关系及其变化趋势。在已有标准A光源测试系统基础上,分别测试氙灯、卤素灯、不同色温白光LED光源发射光谱和红、黄、白、绿、蓝五种逆反射材料的光谱反射率曲线,并通过拟合计算得到同一材料在不同光源照射条件下的相对逆反射系数修正因子。分析结果表明,在可见光范围内具有连续光谱反射率曲线分布的白色材料逆反射系数数值受入射光源光谱变化较小,而单色材料逆反射系数受入射光源光谱差异影响较大,且呈现不同的变化趋势：以卤素光源入射条件下材料逆反射系数测试结果为基础值,不同色温的白光LED、氙灯光源对红色和黄色材料逆反射系数具有正增益效果,且随着光源色温的升高,红色和黄色材料逆反射系数呈下降趋势,降幅最高分别达到47.7%和4.9%;绿色和蓝色材料逆反射系数呈上升趋势,涨幅最高达到16.5%和28.9%。     

Modified perturbation method for eigenvalues of structure with interval parameters

In overcoming the drawbacks of traditional interval perturbation method due to the unpredictable effect of ignoring higher order terms,a modified parameter perturbation method is presented to predict the eigenvalue intervals of the uncertain structures with interval parameters.In the proposed method,interval variables are used to quantitatively describe all the uncertain parameters.Different order perturbations in both eigenvalues and eigenvectors are fully considered.By retaining higher order terms,the original dynamic eigenvalue equations are transformed into interval linear equations based on the orthogonality and regularization conditions of eigenvectors.The eigenvalue ranges and corresponding eigenvectors can be approximately predicted by the parameter combinatorial approach.Compared with the Monte Carlo method,two numerical examples are given to demonstrate the accuracy and efficiency of the proposed algorithm to solve both the real eigenvalue problem and complex eigenvalue problem.     

光谱对小球藻和等鞭金藻生长的影响

采用单色LED光源和荧光灯从效率和速率两个角度研究了光源光谱对海生小球藻和等鞭金藻8701生长的影响,结果表明,连续光谱能够促进较高的最大生长率,蓝光促进生长的效率较高,两者组合能够较好地兼顾效率和速率。为了定量描述光照中的光谱参量,引入光谱吸收系数,根据光源发射光谱和藻体吸收谱计算海藻对光源光谱的量子吸收效率,该系数与实验结果中相应的生长效率成正相关,能够初步以量化形式反映光谱与其生长效率的关系。     

Colour Appearance of Surfaces as Affected by Different Time-Varying Colour-Adaptation Sequences

We report on experiments in which observers judged colour appearance within the context of time-varying colour adaptation. We used pairs of contextual images consisting of a rapid succession of colour surfaces reproduced under different illuminants to analyse the effect of temporal colour adaptation rather than a spatial context on asymmetric matching and also to judge its influence upon the cone excitation components. We used adaptation colour distributions along the red-green and yellow-blue axes (selective conditions) and random colour distributions (non-selective condition). The results of observers’ matches for both conditions showed approximate colour-constant appearance. Although light adaptation did not fully compensate the colour changes, we obtained average colour-constancy index values of 0.6. The results for the two opponent conditions showed similar contextual effects. No significant differences between each condition were found for the L- and S-cone mechanisms and the three test illuminants. On the contrary, some degree of interaction between the comparison-field cone excitations and the colour axis can be seen when the colour mechanisms are analysed separately. This seems to be more pronounced for the S-cone mechanism and suggests that the selective condition of the adaptation sequence may well affect the observer’s chromatic matching response.     

不同波长激发光对血清荧光光谱影响的实验研究

采用日本岛津荧光光度计RF5301,研究了血清的荧光光谱与激发光波长的关系。实验结果表明：在不同波长的紫外光激励下,血清产生的荧光光谱线型及峰值波长基本相同,与激励光波长无关,但荧光峰强度随激励光波长变化而变化。血清的荧光光谱有两个较强的荧光发射区,其中第一个发射区处于300～410 nm,第二个发射区处于410～530 nm。当激发光波长小于310 nm,荧光主要集中在第一发射区,荧光峰位于330和370 nm处,并产生竞争现象。当激发光波长大于250 nm时,只出现330 nm处的荧光峰,其最佳激励光波长为300 nm;当激发光波长大于320 nm,第一发射区的荧光变弱,在第二发射区的荧光变强,荧光峰位于452 nm。此研究为血液的光谱特性研究提供了实验依据,对光诱导荧光光谱诊断技术中激发光波长的选择具有一定的参考价值。     

Optimizing Spatially Localized NMR

Fourier-series windowing, a technique used to obtain spatially localized in vivo NMR spectra, is extended to fields-of-view containing a number of arbitrarily shaped regions of interest. For each volume, k-space weighting functions are derived and then combined to give an overall k-space sampling pattern - the number of signal acquisitions per phase-encoding vector - which can then be used to obtain spatially localized spectra of optimal sensitivity, consistent with a specified degree of localization. The technique is compared with the related methods of chemical-shift imaging and spectral localization by imaging.     

MOVPE 生长GaN薄膜的 光致黄带发光与激发光源的相关性

用四种不同光源作为激发光源,研究了蓝宝石衬底金属有机物汽相外延方法生长的氮化镓薄膜的光致发光特性。结果发现用连续光作为激发光源时,光致发光谱中除出现365 nm的带边发射峰外,同时观察到中心波长位于约550 nm 的较宽黄带发光;而用脉冲光作为激发光源时其发光光谱主要是365 nm附近的带边发光峰,未观察到黄带发光。氮化镓薄膜的光致发光特性依赖于所用的激发光源性质。     

Mesoscopic effect of spectral modulation for the light transmitted by a SNOM tip

The effect of a tapered metal-coated optical fiber terminated by a sub-wavelength aperture (SWA) on the spectrum of the transmitted light is investigated experimentally. Under certain conditions a remarkable spectral modulation of the transmitted light can be observed. This effect is of a mesoscopic origin, occurring only for a certain interval of SWA diameters. One can conclude that a noticeable modulation appears when the number of the transmitted fiber modes is small but exceeds unity, thus indicating the presence of a phase shift between different modes. To discern between two possible sources of such phase shift, the fiber length dependence of the output spectrum has been studied. According to the results obtained for the used sample of 200 nm SNOM tip, the observed phase shift is mostly caused rather by the inherent modal dispersion of the multimode fiber than by the mode-dependent light slowdown in the tapered region close to SWA due to the coupling to surface plasmons of the metal coating. The SWA acts here mainly as an effective mode filter.     

双飞秒激光频率梳光谱测量技术研究进展

双光梳光谱分析技术近年来凭借高分辨率、高灵敏度、宽光谱覆盖和快速测量的优势,在分子和原子光谱分析领域得到了快速发展.从双光梳光谱分析的原理出发,以使用泵浦光源数量为分类依据,对近年来国内外基于不同实现方案的多种双光梳光谱分析技术的原理进行了简要介绍,叙述了在不同数量泵浦光源条件下,不同实验小组提出的多种实验方案,介绍了...     

LED光源光谱对隧道出口段明适应的影响

随着我国经济的不断发展,高速公路隧道建设的发展也非常迅猛。前期在隧道的实际工程设计中,为完全保证隧道车辆通行安全,隧道内部全线灯具的输出功率和安装布置全部取决于一年四季中最大的洞外亮度值和车辆速度值。这样的设计尽管充分考虑了安全性,但盲目的增加隧道照明亮度,不能够缓解视觉适应的问题。随着LED在隧道照明中的应用, LED光源光谱的影响逐渐引起人们的关注。调查研究发现高速公路隧道在出口段交通事故发生率比较高,主要原因是隧道出口段内外亮度差较大,驾驶员在驶离时明适应时间较长。LED光源的光谱呈现双峰结构,在长波长范围内,光谱含量差异明显。明适应的能力主要与两个因素有关,一是瞳孔面积的变化;二是感光色素的光化学反应。不同色温的LED具有不同的光谱特性,进而通过影响感光色素的合成,来影响明适应的时间长短。现在市场上可用的隧道照明LED光源的色温可选范围比较广,所以实验选取了市场上可用的不同色温的大功率的LED光源作为研究对象,其色温分别是3 000, 3 500, 4 000, 4 500, 5 000, 5 700和6 500 K等7种。邀请了30名视觉功能正常,矫正视力1.0以上,且无色盲、色弱等其他眼疾的观察者参加了本次实验。地点选择在长9 m,高2.8 m,宽5 m的模拟隧道内。实验参数选取3组亮度值,分别为4, 8和12 cd·m^-2;2个灯具安装高度分别是2.0和2.4 m;3个安装角度分别是15°, 20°和25°。共评估了126种照明条件。实验结果表明:隧道出口段亮度越大,明适应时间越小;当亮度相同时,随着色温的增大,明适应时间减小;灯具安装角度和安装高度对光谱的影响很小,改变安装高度和安装角度并不能有效的减小明适应时间。从明适应的角度出发,通过分析不同色温LED灯的光谱,为隧道照明设计与应用中出口段LED光源的选择提供数据和理论支撑。     

光谱可调积分球光源的光谱匹配算法研究

基于光谱匹配算法是可调光源产生种类多样光谱分布的必要手段,提出Levenberg Marquardt算法作为光谱匹配算法。利用峰值位置等间隔均匀分布的理想高斯曲线作为LED发光光谱,借助该设定的一系列曲线仿真模拟目标光谱,实验表明,利用该算法模拟太阳、沙漠、海洋和植被的相对光谱分布,相对光谱差异分别为2.17%、1.76%、2.03%、1.7%。利用实验室现有LED的发光光谱进行验证实验,匹配3种目标光谱的相对差异均小于5%。实验结果表明,Levenberg Marquardt算法可应用于光谱可调积分球光源的光谱匹配。     

二维随机介质中的能量分布和频谱特性

研究了二维随机介质中能量的空间分布和一些特定区域的频谱特性.结果显示介质中能量呈局域化分布,其分布与介质中颗粒的随机分布有关,还与激发光的波长有密切的关系,介质中能量聚集的区域和介质的准封闭区域有一定关系但并非一一对应.所考察的各准封闭区域的频谱均随时间变化,在同一激发光的激励下各准封闭区域的频谱均不相同,而同一区域在不同的激发光的激励下频谱也不相同.当激发波长与准封闭区域的结构参数偏差较大时,频谱中谱峰会出现此消彼涨的模式竞争现象,而且能量衰减得较快;而当激发波长与该结构参数较接近时,相应的频谱中存在一 关键词： 激光物理 有限时域差分法 局域化 频谱特性     

Reference Spectra in the “Artificial-Moon” Scale and Cosmological Studies of Radio Sources

We present the modified version of the flux scale [1] of cosmic radio sources. The number of standard sources is increased, the dynamical range of the scale is extended by one order of magnitude toward weak fluxes, and the standard sources are distributed more uniformly over the northern hemisphere. The scale [1] at frequencies above 15 GHz is improved with allowance for additional data. New standard sources are determined in the millimeter wavelength range. The spectra of standard sources are obtained on the basis of accurate absolute measurements of the radiation flux density at frequencies 0.5-10 GHz by the method of an artificial moon. Spectrum shapes of the standard sources were determined by the method of relative spectra based on relative measurements in the frequency interval from 26 MHz to 31.4 GHz. This makes it possible to find spectra in the entire frequency range with an accuracy of 3-4%. We determined the spectra of more than 100 steep-spectrum extra-Galactic sources in the artificial-moon' scale. Most spectra have breaks in the frequency interval from 178 MHz to 14.9 GHz. The spectra of some sources have constant spectral indices. The distributions of the break frequencies of radio galaxies and quasars over celestial coordinates of these sources are obtained. These distributions are close to lognormal. The frequencies of the maxima of radio-galaxy and quasar distributions are equal to 1.25 and 2.5 GHz, respectively. The mean spectral indices as functions of frequency are determined for radio galaxies and quasars. The spectral indices of sources belonging to these two groups increase with frequency at the same rate below 3 GHz. At higher frequencies, the slope of the mean spectrum of galaxies remains the same, while the mean quasar spectrum flattens.     

光电混合机器人视觉系统中光寻址空间光调制器的噪音处理

分析了光寻址空间光调制器对连续图像采样产生的噪音和假频,利用采样理论,提出设置光学去假频前置滤波器抑制噪音和假频的方法.理论分析得出去假频前置滤波器为矩形窗函数的基础上,根据视觉系统中光寻址空间光调制器的参量,计算出了本系统所用的去假频前置滤波器的结构尺寸.视觉系统图像特征提取试验结果表明效果良好.     

基于多光谱和sRGB空间的自然植物色的重现

多光谱成像技术在颜色科学方面的应用主要在于准确的记录和复制拍摄场景的颜色信息。针对目前基于光谱的颜色重现设备昂贵、复杂和实现起来困难的问题,提出了物体颜色从反射光谱空间向sRGB颜色空间变换的方案。在遵循sRGB标准的设备上重现了D65光源下的218种自然植物颜色,所显示的颜色与植物反射光谱实物对应的名称一致。对8个自然植物在9种不同光源下和在sRGB空间下的颜色进行了预测显示。所提出的方案对在网络环境下实现相同实物在不同照明环境下的场景显示提供了可行的途径。