Reflectance and transmittance model for recto-verso halftone prints

We propose a spectral prediction model for predicting the reflectance and transmittance of recto-verso halftone prints. A recto-verso halftone print is modeled as a diffusing substrate surrounded by two inked interfaces in contact with air (or with another medium). The interaction of light with the print comprises three components: (a) the attenuation of the incident light penetrating the print across the inked interface, (b) the internal reflectance and internal transmittance that accounts for the substrate's intrinsic reflectance and transmittance and for the multiple Fresnel internal reflections at the inked interfaces, and (c) the attenuation of light exiting the print across the inked interfaces. Both the classical Williams-Clapper and Clapper-Yule spectral prediction models are special cases of the proposed recto-verso reflectance and transmittance model. We also extend the Kubelka-Munk model to predict the reflectance and transmittance of recto-verso halftone prints. The extended Kubelka-Munk model is compatible with the proposed recto-verso reflectance and transmittance model. In the case of a homogeneous substrate, the recto-verso model's internal reflectance and transmittance can be expressed as a function Kubelka-Munk's scattering and absorption parameters, or the Kubelka-Munk's scattering and absorption parameters can be inferred from the recto-verso model's internal reflectance and transmittance, deduced from spectral measurements. The proposed model offers new perspectives both for spectral transmission and reflection predictions and for characterizing the properties of printed diffuse substrates.     

荧光纸基的双面彩色半色调印刷品Clapper-Yule正面反射率模型

目的研究荧光纸基对双面彩色半色调印刷品反射率的影响。方法假设油墨与纸张的折射率相似,考虑到荧光部分可以吸收光线中不可见的紫外光,经过能量转换散发出可见光从而影响总反射率,将这部分影响等效于正、反面油墨的透射率,以及纸张内部向正、反面反射率的改变;考虑光学网点扩大因子,利用Clapper-Yule分程理论进行分析;通过数值模拟,对新、旧模型进行比较,验证新模型的合理性和准确性。结果建立了荧光纸基的双面彩色半色调印刷品Clapper-Yule正面反射率模型。结论色彩预测Clapper-Yule反射率模型必须考虑荧光纸基的影响。     

彩色双面半色调印刷品光谱反射率与透射率预测模型

为了准确地预测多色双面半色调印刷品的呈色特性,建立一个统一的半色调印刷品光谱反射透射预测模型,对纸张的固有反射率和透射率以及油墨的光谱透射率进行精确的测量和计算.为提高半色调印刷品反射透射预测模型的精度和双面印刷品在线质量检测仪器的开发,提供理论依据.     

调频网印品图像的微观色彩预测模型研究

在考虑网点扩大的情况下,研究了基于Murray-Davies方程的调频网半色调印品色彩预测模型。分析了调频网印品图像的微观结构和特征,建立了理想状态下调频网的反射率模型;考虑到光在纸基中的散射,采用光散射概率理论构建了墨点与墨点间的局部反射与透射关系;最后,建立了基于扩展的Murray-Davies方程的调频网半色调图像的微观色彩预测模型。     

Light scattering and ink penetration effects on tone reproduction

Light scattering, or the so-called Yule-Nielsen effect, and ink penetration into the substrate paper play important roles in tone reproduction. We develop a framework in which the influences of both of these effects on the reflectance and tristimulus values of a halftone sample are investigated. The properties of the paper and the ink and their bilateral interaction can be parameterized by the reflectance Rp(o) of the substrate paper, the transmittance Ti of the ink layer, the parameter gamma describing the ink penetration, and p describing the Yule-Nielsen effect. We derive explicit expressions that relate the reflectance of the ink dots (Ri), the paper (Rp) and the halftone image (R) as functions of these parameters. We also describe the optical dot gain as a function of these parameters. We further demonstrate that ink penetration leads to a decrease in optical dot gain and that scattering in the paper results in the printed image's being viewed as more saturated in color.     

Extending the Clapper-Yule model to rough printing supports

The Clapper-Yule model is the only classical spectral reflection model for halftone prints that takes explicitly into account both the multiple internal reflections between the print-air interface and the paper substrate and the lateral propagation of light within the paper bulk. However, the Clapper-Yule model assumes a planar interface and does not take into account the roughness of the print surface. In order to extend the Clapper-Yule model to rough printing supports (e.g., matte coated papers or calendered papers), we model the print surface as a set of randomly oriented microfacets. The influence of the shadowing effect is evaluated and incorporated into the model. By integrating over all incident angles and facet orientations, we are able to express the internal reflectance of the rough interface as a function of the rms facet slope. By considering also the rough interface transmittances both for the incident light and for the emerging light, we obtain a generalization of the Clapper-Yule model for rough interfaces. The comparison between the classical Clapper-Yule model and the model extended to rough surfaces shows that the influence of the surface roughness on the predicted reflectance factor is small. For high-quality papers such as coated and calendered papers, as well as for low-quality papers such as newsprint or copy papers, the influence of surface roughness is negligible, and the classical Clapper-Yule model can be used to predict the halftone-print reflectance factors. The influence of roughness becomes significant only for very rough and thick nondiffusing coatings.     

具有打底油墨的半色调印刷品的Clapper-Yule模型

通过经典的Clapper-Yule模型的应用,对已有的点对点的半色调印刷品进行扩展,在忽略油墨渗透的条件下,建立起能具有打底油墨的半色调印刷品的呈色规律的理论模型.在假定油墨是非散射介质以及油墨的折射率与纸张的折射率近似相等的近似下,利用光在油墨与纸张中散射迁移路径长短不同的分程理论,建立了具有打底油墨的半色调图像的分程Clapper-Yule光谱反射率模型.     

光谱Neugebauer模型的抗差最小二乘优化

Yule-Nielsen修正光谱Neugebauer模型是一种用来预测彩色网目调印刷品颜色的重要光谱预测模型。为了提高Neugebauer模型预测精度,在分析光谱Neugebauer模型和抗差估计理论的基础上,提出了将抗差最小二乘法用于计算模型参数网点面积率和基色光谱反射率。常用的抗差估计方案有:Huber估计和IGG估计。实验表明,当存在粗差的情况下,与传统的最小二乘法相比,抗差最小二乘法的光谱Neugebauer模型的预测精度更高且更为稳定。     

Rapid simulation of steady-state spatially resolved reflectance and transmittance profiles of multilayered turbid materials

We present a technique for efficiently computing the reflection and transmission of light by arbitrary systems of turbid layers. To approximate the steady-state reflectance and transmittance without the need to solve difficult boundary conditions, we convolve the reflectance and transmittance profiles of individual layers. We extend single-slab boundary conditions to handle index-of-refraction mismatches between turbid slabs and account for interlayer scattering by applying methods similar to Kubelka-Munk theory in frequency space. We demonstrate good agreement between the reflectance and the transmittance predicted by our model and numerical Monte Carlo methods and show that the far-source reflectance and transmittance of multilayered turbid materials are dominated by interlayer scattering.     

Probabilistic spectral model of color halftone incorporating substrate fluorescence and interface reflections

A spectral model incorporating three major physical phenomena, lateral light scattering, substrate fluorescence, and interface reflections governing light-print interaction is presented. In the model, light scattering inside a paper substrate is described by probabilities applicable for any degree of light diffusion. The concept of fluorescence enhanced transmittance has been proven very useful for extending the probability approach to prints on fluorescent substrates. The contribution of multiple internal reflections is accounted for by series expansion of fast convergence. Previously developed models like the Neugebauer equation and the Clapper-Yule model can easily be obtained as special cases of the present model.     

Hemispherical and diffuse reflectance and transmittance of a slightly inhomogeneous film bounded by rough, unparallel interfaces

The optical reflectance and transmittance of an ideal thin film are calculated in a well-known way. As far as a non-ideal thin film is concerned - i.e., a slightly inhomogeneous thin film bounded by rough, unparallel interfaces - three categories of spectral coefficients can be defined, i.e.: specular reflectance and direct transmittance (light intensity flux along the optical axis), hemispherical reflectance and transmittance (light intensity flux integrated over the solid half angle π), and diffuse reflectance and transmittance (light intensity flux scattered around the optical axis) coefficients. In this paper a model recently introduced for the specular and direct coefficients is generalized to calculate also the hemispherical and diffuse coefficients of a non-ideal film.     

基于油墨不同叠印的二阶调频网物理网点扩大的研究

建立了二阶调频网点构成的半色调图像光谱预测模型。考虑油墨在不同叠印条件下由于油墨铺展引起的物理网点扩大,采用Yule-Nielsen修正的光谱聂格伯尔模型对打印的二阶调频网点图像的光谱进行预测,然后计算色度值,并与测量值进行比较。实验结果表明,考虑油墨在不同叠印条件下的铺展的EYNSN模型预测的平均和最大色差分别为2.64和6.21,与未考虑油墨铺展的预测结果相比,预测精度有所提高。     

基于Kubelka-Munk理论的半色调印刷品光谱反射预测模型

首先介绍了经典的Kubelka-Munk理论及其Saunderson校正,并在此基础上推广到半色调印刷品中,考虑到光在印刷品中的横向散射,引入了散射概率函数描述光子从一个界面元进入而从另一个界面元射出的概率,建立了一个统一的半色调印刷品光谱反射预测模型.     

光学变色防伪油墨的颜色预测模型

为更好地研究光学变色油墨的显色性能,加大其在半色调印刷品防伪领域的应用,在分析光学变色油墨变色原理的基础上,着重分析了光变油墨中的薄膜理论,由此建立了一个统一的光学油墨半色调印刷品的光谱反射率预测模型。模型能够很好地预测防伪印刷品和油墨的颜色变化,从而为光变油墨的光谱分析提供了很好的理论依据,能更好地控制防伪油墨的颜色变化。     

基于光散射概率函数的半色调反射率模型

目的以调幅和调频网点为研究对象,针对2种网点分别建立半色调反射率模型,并将网点结构的差异引入模型。方法基于Murray-Davies模型理论推导半色调反射率模型,并以不同光散射概率函数体现不同网点结构。采用数学显微采集系统对半色调印品进行了数字化采集,将数字图像灰度值转化为对应的反射率值,通过分析反射率直方图极值特征得到半色调印品空白反射率和着墨部分反射率,再经数据拟合确定理论推导模型中的参数。结果基于总反射率和光谱反射率的验证实验,结果表明调幅和调频网点模型拟合优度判定系数R2分别为0.9821和0.9520。结论所建立模型能够体现网点结构的差异,精度高,适用性强。     

离子束溅射沉积Co膜光学特性的尺寸效应研究

本文采用离子束溅射沉积了不同厚度的Co膜,利用Lambda-900分光光度计,对不同厚度的Co膜从波长为310nm到1300nm范围测量了薄膜的反射率和透射率.选定波长为310、350、400、430、550、632、800、1200nm时对薄膜的反射率、透射率和吸收率随薄膜厚度变化的关系进行讨论.实验结果显示,Co膜的光学特性都有明显的尺寸效应.对在可见光范围内同一波长时的反射率和透射率随薄膜厚度变化关系的实验结果作于同一图上,发现反射率曲线与透射率曲线都有一个处在网状膜阶段的交点,这个交点对应的厚度作为特征厚度,该厚度可认为是金属薄膜生长从不连续膜进入连续膜的特征判据.     

Single-layer model for surface roughness

Random roughness of an optical surface reduces its specular reflectance and transmittance by the scattering of light. The reduction in reflectance can be modeled by a homogeneous layer on the surface if the refractive index of the layer is intermediate to the indices of the media on either side of the surface. Such a layer predicts an increase in the transmittance of the surface and therefore does not provide a valid model for the effects of scatter on the transmittance. Adding a small amount of absorption to the layer provides a model that predicts a reduction in both reflectance and transmittance. The absorbing layer model agrees with the predictions of a scalar scattering theory for a layer with a thickness that is twice the rms roughness of the surface. The extinction coefficient k for the layer is proportional to the thickness of the layer.     

Diffuse reflectance and transmittance spectra of an interference layer. 2. Evaluation of tin oxide-coated glass

A model for the calculation of diffuse reflectance and transmittance of a single interference layer on a transparent substrate is applied to pyrolytically deposited tin oxide films on glass. Total as well as diffuse reflectance and transmittance spectra were measured in an integrating sphere, and scattering levels between 0.002 and 0.1 were recorded. The optical constants and the thickness of the films were determined from the total reflectance and transmittance spectra. The wavelength-dependent effective root-mean-square roughness of aluminum-coated tin oxide front surfaces was determined by the application of the scalar scattering theory. Surface roughness values between 5 and 25 nm were obtained. The obtained effective rms roughness values of the air-film interface were used together with the other film parameters to calculate the diffuse reflectance and transmittance spectra of the tin oxide-coated glass substrates. A comparison between calculated and experimental spectra showed good agreement for diffuse reflectance, diffuse transmittance, and total integrated scattering spectra.