On the inverse problem in transcutaneous bilirubinometry

Summary Transcutaneous bilirubinometry based on reflectance spectroscopy technique requires the development of suitable optical models of icteric skin and the solution of the inverse problem to derive pigment concentrations from spectral measurements. An algorithm is presented which allows the evaluation of bilirubin concentration during phototherapy. The present analysis shows that quantitative evaluation of bile pigment concentrations during phototherapy can be obtained with a good degree of accuracy by an inverse best-fit procedure; moreover, the knowledge of pigment kinetics makes this method almost independent of other conditions of the skin. The present results refer to the initial part of the phototherapy cycle and are based on a simple model of icteric skin; they may help to extend the application range of commercial transcutaneus bilirubinometer and to investigate the photoconfigurational transient of phototherapy.     

文物红色系颜料高光谱识别指数研究

红色系矿物颜料曾被艺术家们大量地使用在古画和古建筑上.正确地识别出不同种类的红色系颜料对于文物监测与修复具有重要意义.传统的颜料识别主要依靠化学分析,不仅识别速度慢、识别范围小,而且对文物进行取样操作会造成文物的永久损伤.高光谱技术对颜料进行无损识别可以很好地解决这些问题.选用辰砂、胭脂、银朱、朱膘、朱砂、赭石、赭粉、...     

受干扰光谱信息中矿物颜料粒径信息的获取

矿物颜料的准确配色是实现文物壁画高品质修复,颜色高保真还原的关键技术。矿物颜料颗粒的粒径大小是影响矿物颜料颜色信息和光谱反射率信息的一个重要因素。准确获取壁画表面的矿物颜料光谱反射率信息,是实现颜料颗粒粒径信息识别的有效途径。但是,由于壁画表面矿物颜料部分采样点的光谱信息受到了干扰,无法与不同粒径的矿物颜料的光谱数据库准确匹配,因此也无法从采集的光谱信息中获取有效的粒径信息。针对受干扰的颜料光谱信息,提出利用比值导数法对其进行处理。把光谱信息从光谱反射率空间转换到比值导数光谱空间进行匹配,降低光谱中的干扰信息,增强矿物颜料颗粒本身的光谱特征信息。以壁画中常用的不同粒径的石青和石绿矿物颜料为实验对象,制成色块样本,以基底和白色颜料为主要影响因素,对文中提出的方法进行测试。光谱角度量的结果和光谱曲线图的匹配结果显示,在比值导数光谱空间,获得了满意的光谱匹配精度。验证了文中提出的分析方法可以解决实验中受干扰颜料光谱匹配不准确而无法获得粒径信息的问题,能够为壁画修复过程中矿物颜料的配色提供准确的粒径信息参考。     

基于有约束非负矩阵分解的原稿基色色料光谱预测方法

针对直接在光谱反射率空间,对原稿颜色样本光谱的主成分分析会导致特征向量的数目超过真实物理维度(原稿所用基色色料)的数量,以及特征向量和对应系数存在负值,不能直接表示原稿基色色料的光谱特性和对应浓度等情况。创新性的提出需根据原稿色料的光学特性建立一个完全线性的光谱空间,并在该空间中使用带约束条件的非负矩阵分解实现对原稿基色数量和光谱形状进行预测的方法。对此,首先设计了一个实现对原稿基色色料光谱预测方法的总体研究方案和实现步骤,再以透明色料原稿为例,研究如何选择和构建一个符合其光学特性的光谱线性空间,然后再在基本非负矩阵分解(BNMF)基础上提出针对基色色料光谱预测的有约束非负矩阵分解算法(SCNMF)。针对BNMF算法会出现多重最优解,为了提高预测精度,使矩阵分解结果有明确的物理意义,所提出的SCNMF算法需要满足4个约束条件：非负性约束;全加性约束;平滑性约束;稀疏性约束。建立了满足约束条件的目标函数和迭代算法。预测结果表明本文提出的新方法能有效的实现对原稿基色物理维度和基色色料光谱的准确预测。     

有机和无机国画颜料漫反射光谱和吸收光谱特征研究

国画颜料解混一直是古画颜料研究的重要内容,其中光纤反射光谱（FORS）是无损化探测颜料类别的常用手段。通过CCD光纤光谱系统,从光谱线型对国画颜料进行了分类,分别探测了两种有机植物颜料藤黄和胭脂在不同比例混合下的漫反射光谱与吸收光谱,并获取了不同色系无机矿物质颜料混合后的漫反射光谱。分析了单一颜料和混合颜料的光谱特征峰值,运用多元线性回归（MLR）以及一阶导数光谱法（FDS）,通过全波段线性解混获得了各组分颜料的比例。经过实验与理论分析,藤黄与胭脂的漫反射光谱为S型,混合颜料一阶导数光谱中两特征峰的位置分别为536和649 nm,在漫反射光谱中多元线性回归基本适用于该混合颜料的解混并显示出一定的线性规律,但无法精确地解混。而混合颜料的吸收光谱与单色光谱之间存在较好的线性关系,解混误差在5%左右。无机矿物质颜料中的漫反射光谱有S型（石黄和赭石）和钟型（石青和石绿）两种。首先,对于S型（石黄）与S型（赭石）混合颜料漫反射光谱,赭石的一阶导数光谱出现明显的“三峰”现象,并且混合颜料一阶导数光谱在534 nm处出现新的特征峰。多元线性回归理论虽适用于该混合颜料的解混,但由于不同颜料解混的权重因子不同,无法形成较为精准的线性模型。其次,对于S型（赭石）与钟型（石绿）混合颜料的反射光谱需要多元线性回归与导数光谱法共同判断混合比例的基本趋势,该光谱在400～800 nm范围内仅有一个交叉点。最后,利用钟型（石青）与钟型（石绿）混合颜料反射光谱的特征峰位置,即可判断出颜料混合比例的特征,随着混合比例的变化,反射光谱特征峰在457～524 nm出现了明显的横向移动,并且混合颜料光谱的峰值强度有明显的减弱。     

基于可见光谱的古代壁画颜料无损鉴别方法

矿物颜料是古代壁画显色的物质基础,其可见光谱反映自身物质和物理属性。不同颜料对可见光吸收特性的差异导致光谱曲线形状不同,同一种颜料因粒径等级差异引起光谱曲线幅值的规律性变化。依据矿物颜料上述特性,提出一种基于可见光谱的古代壁画颜料无损鉴别方法,通过光谱归一化方法实现不同粒径等级的同一颜料光谱曲线叠合,去除颜料粒径等级对光谱曲线幅值变化的影响,然后提取表征光谱曲线在各波段增减性和凹凸性的一阶与二阶导数特征,与光谱曲线组合得到颜料物质属性鉴别的光谱组合特征空间,以光谱角和欧式距离为基础构建评价指标,计算待鉴别颜料与数据库参考样本在光谱特征空间中的匹配误差(ME),实现颜料物质属性的鉴别。通过构建矿物颜料平均粒径大小和光谱反射率均值之间关系函数,实现颜料平均粒径大小的鉴别。基于构建的古代壁画常用颜料光谱数据库,以莫高窟壁画为对象,通过非接触式原位无损测量方法测量获得壁画颜料的可见光谱数据,对本文方法进行了验证,并以石绿和青金石颜料的鉴别结果为例,对古代壁画颜料使用技法、不同朝代颜料使用的差异性及原因进行了探讨。该方法将为更加全面深入研究和保护古代壁画提供有效的理论与方法支撑。     

Analysis of skin surface roughness by visual assessment and surface measurement

In this study, we analyze the surface roughness of human skin using human visual assessment and statistical features of three-dimensional shape data and goniometric reflectance data. We use eight skin replicas taken from the cheeks of women. First, we perform human visual assessment to obtain the roughness rankings. Second, we measure three roughness parameters by currently used methods. These parameters show no significant correlation with the roughness rankings. Third, we measure the skin surface shape to calculate surface normal vectors. We show that the surface normal distribution of the skin is isotropic and Gaussian, and the standard deviation has a good correlation with the roughness rankings. Finally, we analyze the goniometric reflectance data to approximate the surface reflection using the Oren-Nayar model. We find that the standard deviation estimated using this model corresponds to the roughness rankings. Thus, this parameter can be effectively used for describing skin roughness.     

Influence of the Concentration of Aqueous Solutions of Sulfuric Acid on the Reflection Spectra of Pine Needles

The effect of solutions of sulfuric acid of different concentrations on the optical characteristics of pine needles was investigated. It is found that an increase in the acid concentration results in a decrease in the content of pigments in pine needles and in their reflectance in the visible region. An analysis of experimental data by using the LIBERTY model has shown that the decrease in the pine needle reflectance with decrease in the pigment content depends on the change in the refractive index at the cell wall–binding medium interface.     

Simulation of spectral reflectances in human skin tissue using ray tracing and GPU-based Monte Carlo method

We study a simulation of spectral reflectance in human skin tissue using ray-tracing software and the Monte Carlo method on the basis of a graphics processing unit (GPU). An analysis of light propagation using ray-tracing software has several advantages in that it can readily reproduce the complex structure of skin tissue, such as grooves of the skin surface or the boundaries of skin tissue layers, and perform optical simulation with optical elements close to those in a real experiment using only the ray-tracing software. Meanwhile, it has a serious disadvantage in that the simulation time is extremely long because the algorithm is CPU-based. To overcome this disadvantage, we propose a simulation method using the ray-tracing software and a GPU-based Monte Carlo simulation (MCS). The results of the simulation are shown and discussed.     

光导纤维反射光谱技术在彩绘文物颜料无损分析鉴定中的应用

文物颜料成分分析鉴定是文物材质分析和文物保护工作的重要内容。利用自行研制的光导纤维反射光谱仪对唐代彩绘陶器和壁画上的颜料成分进行了无损分析鉴定,通过比较彩绘文物颜料和标准颜料的反射光谱曲线的形状以及特征峰或一阶导数峰来完成颜料的鉴定工作。光导纤维反射光谱法鉴定出西安市唐代彩绘文物1#样品墓葬壁画上的深红色颜料是纯度较高的土红;2#样品陶器残片上的绿色颜料为石绿;3#样品陶缸残片上的橙红色和朱红色颜料分别是由大量铅丹和微量土红及大量朱砂和微量土红的混合物所组成。采用X射线荧光分析法进行验证,实验结果表明光导纤维反射光谱技术鉴定彩绘文物颜料成分的结果是准确、可靠的,提供了一种文物颜料无损分析的简捷方法。     

Analytical model of phototherapy for neonatal jaundice. Influence of bilirubin kinetics on skin colour during phototherapy

Summary Recent progress in diode-array detector technology and signal processing methods, and in the optical modelling of tissues allow: i) real-time, multispectral analysis of reflected spectra with relatively simple and compact devices; and ii) improved correlations between reflectance spectra and pigment distribution in tissues. Second-generation transcutaneous bilirubinometers relying on the changes in the optical properties of the skin at selected wavelengths due to changes in its optical components are being developed. To extend the use of transcutaneous bilirubinometry to the phototherapy cycle, the modelling of the complex mechanisms of bilirubin photochemistry and metabolism in the various body compartments is required. As a first step toward this aim, the influence of bilirubin photochemistry occurring during the initial stage of phototherapy on the reflectance spectrum of an icteric tissue is analysed. A four-layer model is assumed. The transformation of bilirubin into its configurational isomers is considered in detail, while the role of the structural isomer on bilirubin elimination is taken into account with a loss term in the equation of motion of bilirubin concentration. The phototherapeutic process makes the illumination in the bile pigment layer depend on time. However, in the specific cases here considered, this time variation is negligible, and the differential equations describing the time evolution of bile pigment concentrations can be solved in a closed form. The bilirubin kinetics produces significant changes of the diffuse reflectance spectra during phototherapy, and the difference of the colour after the phototherapeutic treatment of a known duration can be put in close correspondence with the model of the jaundiced skin and permits quantitative estimates of pigment concentrations.     

Optical path-length matrix method for estimating skin spectrum

In this article, we propose a new method??the optical path-length matrix method (OPLM)??as a faster alternative to the Monte Carlo for multi-layered media (MCML), which is often used to simulate the skin spectrum. Theoretically, peripheral oxygen saturation can be estimated by iterating MCML, but it is not a realistic strategy because it requires huge computation time. The optical path-length matrix is obtained as the probabilistic density histograms of the optical path length in skin using MCML, and once the matrix is obtained, skin spectral reflectance can be calculated by accumulating all combinations of elements in the matrix and by setting an absorption coefficient based on the Beer-Lambert law. The computational time of OPLM was approximately 26,000 times faster than that of MCML.     

唐卡主色矿物颜料光谱分析

唐卡作为一件艺术品,具有较高的历史价值和艺术价值。对唐卡的矿物颜料进行鉴别分析,对唐卡的鉴定、修复、数字化存档、再现等具有非常重要的意义。该研究对唐卡主色矿物颜料进行体系性的光谱分析,选用唐卡绘制过程中5种主色常用的矿物颜料,深入分析矿物颜料的可见光、近红外、短波红外光谱特征产生机理,总结了不同色系矿物颜料可见光、近红外、短波红外谱段光谱特征。通过分析同一矿物颜料粉末、调和骨胶颜料以及颜料上布色卡光谱特征,发现粉状颜料调和骨胶后,反射率整体下降,在1 447和1 928 nm附近出现两个水的强吸收特征。而当骨胶溶物涂绘上布后,随着膏状颜料中水分的减少,上述两个吸收特征均变弱,个别颜料在1 447 nm处的吸收特征甚至消失。因此,矿物颜料粉末和颜料上布色卡光谱极为接近,可以在后期的唐卡颜料分析中直接利用唐卡矿物颜料粉末光谱进行匹配分析。唐卡红色矿物颜料为朱砂,矿物成分主要为HgS,其光谱在可见光波段先降后升,500 nm附近形成一个较深的吸收特征,且吸收峰较宽（430～530 nm）,红光谱段附近反射率急速升高,近红外波段反射率变化较为平直,在1 940和2 250 nm附近有弱吸收特征。唐卡黄色矿物颜料主要有三种：土黄（雄黄、雌黄）,赭石及金箔,主要成分分别为硫化砷、氧化铁及金。其特征光谱在可见光谱段集中在400～500 nm之间,不同颜料的吸收特征位置和吸收深度均不同。赭石在近红外波段的反射率整体较低,且860 nm附近还出现了吸收特征;而雄黄、雌黄和土黄则在近红外和短波红外谱段表现出反射率较高且波形平直,在1 890和2 230 nm附近有弱吸收特征;金箔在可见光波段的吸收特征窄浅,可作为区分的依据。唐卡蓝色矿物颜料为石青,主要矿物成分为蓝铜矿,其光谱在500～1 000,1 500,2 040,2 285和2 350 nm附近均有较强吸收特征,而在1 885和1 980 nm处有弱吸收特征。唐卡绿色矿物颜料为石绿,主要矿物成分为孔雀石,其光谱在550～1 000 nm有较强的宽吸收特征,在2 270和2 350 nm有明显吸收特征。尽管石青和石绿主要矿物成分皆为碳酸铜,但石绿在900～1 900 nm红-近红外谱段反射率增加较缓,1 500 nm无吸收特征,可以作为区分石青和石绿的依据。唐卡白色矿物颜料为砗磲和白土,主要矿物成分分别为碳酸钙和高岭土。在可见光谱段范围,砗磲在370 nm有弱吸收特征,而白土则在370和730 nm处有两个明显的吸收特征,可作为区分。在短波红外和近红外谱段,白土在1 425,1 930和2 230 nm均具有明显吸收特征,砗磲则在1 930和2 320 nm有明显吸收特征,1 440 nm处吸收特征较弱。且同种矿物颜料粉末,矿物粉末颗粒越大,颜料颜色越深,其光谱特征反射率越低。     

Measurements and analysis of antireflection coatings reflectivity related to external cavity lasers

Facets of semiconductor optical amplifiers (SOA) designed for external cavity lasers must be coated with an antireflection (AR) film of high quality and extremely low reflectance. Therefore measurements of facet reflectance play a crucial role in the fabrication of such AR coating. The reflectance can be estimated by studying the optical power reflected from the Fabry-Perot cavity formed for that purpose by the examined SOA facet and the end of a single-mode fibre. We have made analysis of practical suitability of such measurement method. Theoretical calculations show that, for the low reflectance coatings, losses due to light coupling into optical fibre cannot be omitted in the analysis of the experimental results. To verify this conclusion a theoretical model was tested for a low reflectance surface and we have found that the relative error of the measurements supported by the theoretical model is on the order of 8%.     

Evaluating a Multi-Spectral Imaging System for Mapping Pigments in Human Skin

A multi-spectral imaging system is evaluated for mapping melanin density, total-hemoglobin density, and oxygen saturation in human skin. In this system, the distribution of pigments in human skin is estimated and displayed from digital video signals using three pre-computed “look-up” tables for color conversions. The accuracy of the system is analyzed based on computer simulation by changing the number of bands, quantization levels of the camera system, and dimensions of approximation for spectral reflectance. The optimal system is examined based on the results of computer simulation.     

Diffuse reflectance of TiO2 pigmented paints: Spectral dependence of the average pathlength parameter and the forward scattering ratio

Diffuse reflectance spectra of paint coatings with different pigment concentrations, normally illuminated with unpolarized radiation, have been measured. A four-flux radiative transfer approach is used to model the diffuse reflectance of TiO₂ (rutile) pigmented coatings through the solar spectral range. The spectral dependence of the average pathlength parameter and of the forward scattering ratio for diffuse radiation, are explicitly incorporated into this four-flux model from two novel approximations. The size distribution of the pigments has been taken into account to obtain the averages of the four-flux parameters: scattering and absorption cross sections, forward scattering ratios for collimated and isotropic diffuse radiation, and coefficients involved in the expansion of the single particle phase function in terms of Legendre polynomials.     

Independent Component Analysis of Spectral Absorbance Image in Human Skin

The image of spectral absorbance in human skin is analyzed by independent component analysis. The spectral absorbance image is estimated from an image with red, green, and blue channels. The qualitative information and spatial distribution of the pigments can be extracted by the independent component analysis. It is shown that the extracted absorption characteristics of the pigments are corresponding to those of hemoglobin and melanin.     

基于独立成分分析法ICA的多光谱重建

构造了一个6通道,8-bit多光谱相机(MSC)模型作为图像采集装置(包括一个三色数码相机和一个滤光片),在多光谱成像技术基础上,通过模拟相机的数码响应,对物体表面的反射光谱进行重建。由数码相机的响应值得到物体的光谱反射比。使用独立成分分析法来进行数据压缩,光谱重建结果分别用CIE1976色差,光谱反射比RMS误差和反射比相对误差进行评价。20例训练样本的平均CIE1976色差为0.1579,平均反射比均方差为0.0099,平均反射比相对误差为0.0107;12例待测样品的平均CIE1976色差为0.7150,平均反射比均方差为0.0309,平均反射比相对误差为0.0312。结果说明,基于独立成分分析法的光谱重建是一种有效的光谱重建方法。     

中国古画矿物颜料光谱混合模型初探-以石青和石绿为例

高光谱遥感技术对文物完全无损,适于对中国古画等文物进行颜料的鉴别与分析,但是中国古画中混合颜料不同成分的定量分析仍然是文物颜料分析领域中的难点。针对中国古画中经常出现的混合颜料现象,以石青、石绿两种典型的矿物颜料为例,选用粒度大小相同的两种矿物颜料粉末,按照不同的体积比例精确配比获取颜料样本,然后精确控制实验条件获取其光谱。对混合光谱分别用全约束最小二乘法进行全波段光谱解混,用比值导数解混算法进行单波段光谱解混,然后评定解混精度并对解混结果进行对比分析,探讨这两种矿物颜料的光谱混合模型。实验结果表明,石青、石绿两种矿物颜料的光谱混合从总体上来说非线性混合特征较强,但是在局部某些波段又基本符合线性混合模型,利用这些波段采用比值导数法解混,可以得到远高于全波段解混精度的定量分析结果。     

基于光谱表示和独立成分分析的混合颜料成分分析方法

在混合颜料成分分析中,反射光谱法通过计算相似性来判断基本颜料种类,容易受多种基本颜料的影响,造成分析结果不准确。将光谱表示为信号,结合独立成分分析,提出一种基于光谱表示和独立成分分析的混合颜料成分分析方法。首先,采用光谱仪获取混合颜料光谱信息,并将其表示为离散信号的形式;然后,对信号进行独立成分分析,得到基本颜料的光谱信息;随后,通过计算基本颜料光谱与已知颜料光谱的相似性,确定基本颜料种类;最后,逆用Kubelka-Munk混色公式就可以得出基本颜料的比例。我们采用蒙赛尔色卡光谱制作模拟数据,分别进行正常/扰动情况下三种色卡光谱混合信息的成分分析试验,以及从8种色卡光谱中选择若干种混合后的成分分析实验。分离出的光谱形态与已知的原始颜料光谱形态极其相似,平均相似比为97.72%,最大相似比可以达到99.95%,得出的基本颜料比例与混合时的比例基本相同。实验结果表明本方法适用于混合颜料成分分析。