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。     

Stress and fracture analysis in periodic contact problem for coated bodies

The periodic contact problem for the system of dies and two‐layered elastic foundation is considered. The imperfect adhesion between the layer and the substrate is taken into account by the boundary conditions at the interface. The solution of the problem is based on Hankel transform and the methods of localisation and superposition. The results are used to evaluate internal stresses in coated bodies which are in contact with rough surface and to analyse the influence of mechanical and geometrical characteristics of the coatings and the roughness parameters on the maximum stress value and its location, and on the types of coating fracture.     

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.     

Clapper-Yule光谱预测模型

详细介绍了经典的Clapper-Yule模型以及其改善的模型--分程Clapper-Yule模型和点扩散Clapper-Yule模型,并在此基础上介绍了Clapper-Yule模型的扩展应用:将Clapper-Yule模型扩展到粗糙承基质和荧光半色调印品上,同时分析了各个模型的特点,最后进行前景展望.     

Diffuse reflectance and transmittance spectra of an interference layer: 1. Model formulation and properties

A model for the calculation of the diffuse reflectance and transmittance of a single interference layer with rough interfaces on a transparent substrate is presented. The model is based on electric field calculations and scalar scattering theory, and it assumes that the interfaces of the layer are totally uncorrelated. Examples are given of calculated spectra in which the parameters of the model are varied systematically to show the influence from different interface roughness and refractive index combinations as well as absorption in the film. A wavelength-dependent effective root-mean-square roughness is introduced. This depends on the nature of the roughness, and the bandwidth limits are given by the experimental conditions. Finally, total integrated scattering spectra are calculated and the importance of taking multiple reflections in the substrate into account is shown.     

Influence of orientation of rough grooves on spectral reflectivity of a surface in the thermal radiation wavelength range

Roughness is one of the principal factors influencing reflectance of a surface that takes place in radiation heat transfer. In the present work, we investigate the influence of the orientation of single-oriented roughness grooves on the directed–directed spectral reflectance of surfaces within the wavelength range of 0.2–20.0 μm. The surfaces have a mean square deviation of the roughness (σ) of 0.2 μm and 2.0 μm and the areas exceed the size of the incident light beam. The angles of reflection are equal to the angles of incidence and are equal to 50° and 70°. The degree of influence of the groove orientation on the reflectance is defined as the ratio of the reflectances of one and the same surface with the grooves oriented parallel and perpendicular to the plane of incidence. In the theoretical investigation, we engage the unidimensionally rough surface model. An experimental study by means of physical modeling was performed: the degree of influence of the groove orientation on the spectral reflection of the surface was estimated, within the investigated wavelength range, according to the degree of influence of the groove orientation on the monochromatic reflectance of the reference ground surfaces within the σ-range of 0.01–4.33 μm on the wavelength 0.405 μm. The studies performed show that the spectral range of the groove orientation influence on the surface reflectance increases with an increase in σ and a decrease in the angle of incidence; the degree of that influence has a maximum the value of which increases with the increase in the angle of incidence. We determine the conditions of agreement of the theory and the experiment.     

商标印刷色彩预测 Clapper-Yule 模型

把油墨与纸张等价为吸收薄膜,考虑光在纸基油墨间多重内反射和横向传播,运用吸收膜理论,建立了半色调商标印刷品的Clapper-Yule 色彩预测膜层模型。通过数值计算并与实验值比较,证明了新模型的预测精度明显高于之前的Murray-Davies 模型,而且改进了经典Clapper-Yule 模型预测偏暗的问题。     

Light Scattering by Composite Rough Surfaces

Abstract

Light scattering from a dielectric surface with composite roughness is considered, where the surface irregularities are modelled as a superposition of two roughness types of different length scales. Geometrical optics and the Rayleigh-Rice expansion, respectively, are employed in describing the scattering from the two roughness structures. Contrary to previous work, we concentrate on bistatic cross-sections, which are calculated analytically for scattering in the plane of incidence, and resulting plots for various parameter values are shown, especially for small-scale correlation lengths of the order of the wavelength of the incident light. The main effects of the small-scale roughness are an overall decrease of the coherent reflectance and a depolarization of the scattered light, which in the plane of incidence is not present for scattering from a surface with a single scale of roughness. It is, however, concluded that scattering at the surface and volume scattering have to be taken into account in order to explain the experimentally found degrees of depolarization.     

Experimental light-scattering measurements from large-scale composite randomly rough surfaces

We present experimental measurements of the angular distribution of light scattered from large-scale composite randomly rough surfaces (oceanlike surfaces) with different statistical parameters illuminated at small and large angles of incidence. The surfaces are composed of a small-scale roughness superimposed on a slowly (large-scale) varying surface. The large-scale surfaces are diamond-machined periodic surfaces made on aluminum substrates and have either a sinusoidal or a Stokes wave profile. The small-scale roughness is added with microlithographic techniques, and the surfaces are then gold coated. For a linearly polarized incident beam, it is found that the diffusely scattered light is strongly depolarized and that its pattern is rather different for each large-scale surface profile. Enhanced backscattering is also observed.     

荧光油墨印刷品的预测模型

荧光油墨半色调印刷品的显色预测规律是彩色成像领域内十分关键的课题.详细介绍了荧光油墨印刷品的经典Clapper-yule预测模型以及其改善的模型分程Clapper-yule预测模型,并且介绍了基于点扩散的Clapper-yule预测模型.同时分析了各个模型的特点,最后进行前景展望.     

基于荧光基Clapper-Yule光谱模型的墨层厚度变化预测

由于荧光纸基会吸收紫外线,激发可见蓝光或可见紫色荧光,而影响墨层厚度,为此基于荧光纸基的Clapper-Yule光谱反射色彩预测模型,考虑了荧光纸张的光学特性、光在荧光纸内部横向传播等特性,采用最小二乘参数估计方法,通过印刷品光谱反射率反映荧光纸基的墨层厚度变化量。该模型可为彩色印刷品的呈色规律分析和印刷品质量检测系统的研制与开发提供一定的理论依据。     

Determination of height distribution on a rough interface by measuring the coherently transmitted or reflected light intensity

In this work it is shown theoretically and examined experimentally that the measurement of coherently transmitted or reflected monochromatic light intensity from a randomly rough interface as a function of incident angle provides the height distribution on the interface. It is also shown that the spectrum of coherently transmitted or reflected light from a rough interface is modified and the modified spectrum yields the height distribution. The experimental results obtained by applying both methods, in transmission and reflection, on rough surfaces prepared by roughening the sheet glasses by powders of different grain sizes are quite consistent. In addition, the effect of the surrounding medium's refractive index on the roughness measurement is studied by immersing the samples into liquids of different refractive indices. Also, the application range and limitations of the introduced methods are discussed.     

Black layer coatings for the photolithographic manufacture of diffraction gratings

A black layer coating for an aluminum-photoresist interface with a reflectance less than 0.1% for 413-nm, s-polarized light incident at 25 degrees is described. It is made of space-compatible materials, and its rms roughness is less than 15 A.     

Backscattering measurements from double-scale randomly rough surfaces

We present experimental measurements of light backscattered from double-scale randomly rough surfaces (oceanlike surfaces) with different statistical parameters illuminated at small and large angles of incidence. The surfaces are composed of a small-scale roughness superimposed on a slowly (large-scale) varying surface. The large-scale surfaces are diamond-machined periodic surfaces made on aluminum substrates and have either a sinusoidal or a Stokes wave profile. The small-scale roughness is added with lithographic techniques, and the surfaces are then gold coated. For a linearly polarized incident beam, it is found that the backscattered light is strongly depolarized mainly at small angles of incidence and strong shadowing effects are present for large angles of incidence (θ(inc) > 60°).     

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.     

单色半色调墨点非规整Clapper-Yule分程模型

目的 研究非规整的墨点（非二值理想墨点）形态对光谱反射率的影响, 为预测模型的理论研究提供一个新的思路。方法 通过讨论墨点的非规整形态对网点大小、 厚度及油墨透射率的影响, 采用二维高斯函数模拟墨点表面的形态, 由此建立一个Clapper-Yule扩展模型。结果 模型的数值模拟结果表明墨点的非规整性导致了网点的物理扩大, 增加了油墨对光的吸收, 降低了最终的光谱反射率。结论 采用Clapper-Yule分程模型对颜色进行预测时需考虑墨点的非规整所带来的物理网点扩大, 该模型适用于单色半色调的颜色预测与控制。     

Controlled frustration of total internal reflection by electrophoresis of pigment particles

A model based on geometrical optics has been developed to describe the photometric observations associated with a novel method to control the reflectance of a surface. In this new reflectance modulation approach, electrophoresis of pigment particles is used to absorb light reflected by total internal reflection (TIR). The pigment particles are sufficiently small that they substantially do not scatter light, but rather they modify the effective refractive index at the reflection interface. An incident light ray interacting with this modified effective index is attenuated in a spectrally selective manner. Although frustrated TIR has been understood and used in various applications for some time, in this case it is used to substantially modify the color of the reflected light, which to our knowledge has not been previously reported. A numerical model of the pigment particle distribution has been developed to describe the observations.     

Effect of surface roughness on measurement of light distribution in intralipid suspension

Light distribution in the biological tissue phantom intralipid suspension with different interface roughness was measured for quantitative understanding of surface roughness effect. The results show that the surface roughness strongly affects light distribution inside the approximately semi-infinite biological tissue phantom. The phantom surface possesses a certain degree roughness and the effect of the surface roughness on measurement results of light distribution in tissue is substantial, so the measurement of light distribution in biological tissue needs to take surface roughness into account.     

Transparent superhydrophobic surfaces for applications of controlled reflectance

This work involves a new optical application for transparent superhydrophobic materials, which enables low-energy optical contact between a liquid and solid surface. The new technique described here uses this surface property to control the reflectance of a surface using frustration of total internal reflection. Surface chemistry and appropriate micro-scale and nano-scale geometries are combined to produce interfaces with low adhesion to water and the degree to which incident light is reflected at this interface is controlled by the movement of water, thereby modifying the optical characteristics at the interface. The low adhesion of water to superhydrophobic surfaces is particularly advantageous in imaging applications where power use must be minimized. This paper describes the general approach, as well as a proof-of-principle experiment in which the reflectance was controlled by moving a water drop into and out of contact with a superhydrophobic surface by variation of applied electrostatic pressure.