【作者】 赵晨飞；

【导师】 韩卿；

【作者基本信息】 陕西科技大学 ， 制浆造纸工程， 2014， 博士

【摘要】 印刷的质量受印刷机、油墨、纸张的影响，而纸张对印品质量的影响很大，纸张的成本在印刷品成本中占很大的比例，因此很有必要研究纸张对印品质量的影响尤其是色彩的影响。目前印刷质量的控制主要有灰平衡控制和色彩管理，而先进的色彩管理方式是光谱色彩管理。论文对纸张的性能对印刷效果的影响进行了研究，重点针对印刷色彩控制的相关内容进行了研究，包括纸张色彩对印品色彩的影响分析、纸张印刷品黄、品、青油墨单色网点面积的预测、纸张印刷品的灰平衡控制及纸张印刷品的色彩管理。纸张的印刷适性（包括纸张的物理性能、光学性能、机械性能、化学性能）对印品的质量，如阶调、层次、清晰度、颜色等有重要的影响。在印刷中需要对纸张的印刷效果进行评价。基于测试图的纸张印刷性能评价法比较直观，在使用不同纸张、其它印刷条件都相同的情况下印刷，得到不同印品。通过观察测试图的变形情况来判断纸张的印刷适性。利用计算机图像可以对纸张的匀度进行分析，对纸张印刷品图像中各个像素点的灰度值进行统计，做出灰度分布的直方图。直方图中，灰度分布得越窄，说明纸张的匀度越好。把纸张印刷品电子图像的一些物理性质进行检测，包括圆度偏差、边缘粗糙度等，可以评价喷墨印刷纸张的毛细管现象、羽化现象、渗透现象等。这种基于图像法的纸张评价方法适合在线检测。利用BP神经网络对不同质量胶版纸的性能和印刷效果进行训练，可以对胶版纸及其它纸张的印刷适性进行评估，这种方法具有速度快的特点。纸张的平滑度、光泽度、白度与印品色彩有很好的相关性。在造纸过程中使用的原料的颜色不纯净、有杂色，或者经过漂白的纸浆的颜色也会略带有一些浅黄、浅绿的颜色，所以要经过调色与增白处理。调色就是在纸浆中加入微量的补色染料，增白处理一般要加入一定量的荧光增白剂。由于浆料及造纸工艺上的差异，形成了纸张颜色的差异。白度是纸张的一个重要的光学性能，当光线照到纸面上，会发生反射、折射、散射、吸收现象，测定这些光线在特定条件下的通过量就可得到纸张的光学性能。纸张白度的测量主要是以波长在457nm（约380-510nm）为中心的光波照射在试样上的反射率来衡量，这种方法没有考虑人眼的视觉特征。因此在印刷中用L*a*b*值来表征纸张的颜色，即能直观的反映纸张的白度和色偏，又能与人眼对颜色的视觉一致。当纸张的底色不是纯白色时，纸张上所印色块呈现的颜色可以说是油墨的颜色和纸张的颜色混合后的综合颜色，这样一定会出现纸张的底色引起的偏色现象。在这种情况下，印刷厂的工作人员必须根据原稿的内容和色彩进行分析，并要采取一些措施来进行纠正色彩，排除纸张的干扰。为了符合光谱色彩管理的研究趋势，需对纸张的颜色参数特征化，采用在可见光波长范围内的反射率来表示纸张和印刷品的颜色，研究纸张的光谱反射率与印品的反射率的关系。结果表明，纸张的光谱反射率与单色印品的光谱反射率是线性相关的，纸张的光谱反射率与多色印品的光谱反射率不是线性相关的。目前数字印刷发展迅速，尤其是喷墨印刷发展很快，喷墨印刷主要使用水性油墨。在数字印刷中存在网点扩大现象。喷墨印刷的网点扩大主要是光学网点扩大和物理网点扩大。光学网点扩大主要是纸张内部的光线的物理反应引起的，而物理网点扩大主要是油墨在纸张上的铺展和渗透引起的。在喷墨印刷中，青油墨主要吸收570-700nm的红光，反射400-570nm的蓝光和绿光。青油墨的高反射区是400-570nm，选取高反射点为480nm，低反射区为570-700nm，选取低反射点为630nm。品红油墨主要吸收500-600nm的绿光，反射600-700nm的红光和400-500nm的蓝光；品红油墨的高反射区为600-700nm的红光和400-500nm的蓝光，选取高反射点为680nm，低反射区为500-600nm的绿光，选取低反射点为530nm。黄油墨主要吸收400-500nm的蓝光，反射500-700nm的绿光和红光。黄油墨的高反射区为500-700nm，选取高反射点为680nm，低反射区为400-500nm的蓝光，选取低反射点为430nm。通过分析黄、品、青油墨的光谱反射曲线，可以发现：各色油墨的高反射点与低反射点反射率之差除以相应油墨的高反射点与低反射点的反射率之和与油墨的网点面积率极为接近，因此可采用归一法的方法预测青、品、黄的网点面积值。在研究中，比较了不同纸张对网点面积值的差别，发现：纸张偏青的话，则预测的青油墨网点面积值大些；纸张偏品红的话，则预测的品红油墨网点面积值大些；纸张偏黄的话，则预测的黄油墨网点面积值大些。尤尔-尼尔森光谱聂格伯尔(YNSN)模型描述了网点与印品的光谱反射率之间的关系，通过测量印品的光谱反射率可以预测网点面积，是一个理想的模型。为了更好的应用YNSN模型预测网点，需要确定其修正指数。在预测浅色调单色网点面积时，采用纸张的光谱反射率的倒数作为修正指数，利用最小二乘法对网点面积率进行预测，实验结果表明，预测精度良好。在光谱色彩管理中，需要对不在特征文件中的多色印刷的光谱反射曲线与油墨网点面积进行转换，该过程参数多，计算量大，难度大。在研究中，利用BP神经网络进行色彩转换。可以把光谱区间进行分段取点以表征不同颜色的光谱变化。把430nm、480nm、530nm、580nm、630nm、680nm的反射率作输入值，大大减小了训练的数据量，这种配色模型称为改进的基于光谱的BP色彩转换模型。基于光谱颜色空间模型采用Levenberg-Marquardt （L-M）优化算法，训练函数为trainlm，经过迭代后，满足了均方根误差小于0.1×10-3的要求，网络训练结束。为了寻找超色域色彩的转换方法，研究了单色、双色、三色油墨色块的光谱反射曲线图，来寻找色域特征。青油墨的波峰在420nm到560nm波长之间，网点面积值越小，在各个波长点的光谱反射率越大，尤其是在580-730nm波长处，网点面积差别越大，光谱反射率差别越大。且网点面积值为0-100%的青色油墨的色域处于最上面的光谱反射曲线（网点面积为0%）和最下面的光谱反射曲线之间（网点面积为100%）。青色油墨和黄色油墨的叠印，波峰出现在490-540nm波长处，在560-620nm波长处出现轻微的波谷，在630-730nm波长处的光谱反射率轻微变化。当青、品、黄三色油墨叠印时，随品红油墨的增加，波峰逐渐前移，且波长在380-630nm时，光谱反射率随着减少，且在波谷处的下降最大。品红油墨一定时，随着黄油墨的网点面积率的增加，在380-480nm波长处，光谱反射率下降多，而在其它波长处，光谱反射率轻微下降。双色叠印色（青和品红叠印色），随着品红油墨的网点面积的增加，反射率在380-560nm的波峰处变小，在540-580nm波长处形成波谷，在590-730nm波长处光谱反射率基本不变。对于色彩转换，可以寻找色相、明度和饱和度与光谱反射曲线的关系。判断颜色是否在光谱色域内。如果不在的话，先根据光谱特征判断属于哪几种油墨的叠印，然后找到相关的色域，再根据印品选择是同色相压缩还是明度压缩还是饱和度压缩的方法，确定其中的高度、宽度或波峰的位置，再找出最近的曲线来代替即可。研究灰平衡数据可以使印刷品避免出现色偏的现象。目前有基于密度和色度的灰平衡数据的计算方法，没有基于光谱反射率做参数的灰平衡数据计算方法。根据灰平衡的一些基础知识，测量在可见光波长范围内相同青、品、黄油墨含量时的光谱反射率和黑墨的反射率，并作比较分析。利用Matlab软件进行BP神经网络训练，可得到灰平衡时青、品、黄油墨的实际网点百分比。更多还原

【Abstract】 The printing machine, ink, paper has the great influence on printing quality.The paper’s cost is high, and it has the effect on printing quality especially oncolor. The color control of printing quality is mainly gray balance and colormanagement, and the most advanced color management is the spectral colormanagement. The effect of the performance of the paper on the printing’s effectis studied, focusing on the relevant content of printing color control, includingthe impact of paper’ color on printing’s color, single color ink’s dot area value’sprediction, the paper printing’s gray balance control and paper printing‘s colormanagement.The printing paper’s printability which includes physical property, opticalproperty, mechanical property, chemical property and so on has important effectson print’s quality, such as tone, hierarchy, clarity, color. It is necessary toevaluate the quality of the paper by its print effect.The test graph which is used to evaluate the paper’s printing performance.The graph is obtained by printing on different paper under the same printconditions. Through observing the deformation of test graph the printability ofpaper can be determined. By using computer image analysis the paper’sformation can be carried out. The gray level value of each pixel in the image ofpaper printing is statistical, and the gray distribution histogram is made. In thehistogram, gray distribution is narrower, the evenness of paper is better. Somephysical properties of the paper printing’s electronic image is detected, includingroundness deviation, edge roughness, capillary phenomenon, the ink-jet printingpaper’s emergence phenomenon, osmosis phenomenon can be evaluated. Thiscomputer image method for evaluating is suitable for online detection. Differentquality’s offset printing paper’s property and printing effect is trained by BPneural network, offset paper and other paper’s printability can be evaluated.Thismethod has the characteristics of fast speed. Paper’s smoothness, gloss, whiteness has good correlation with printingcolor. In papermaking the raw material’s color is not pure and with mottled, orbleached pulp color will be slightly some pale yellow or light green color, socoloring and whitening treatment is needed. Color is to add color dye trace in thepulp, and whitening treatment is to add fluorescent whitening agent. Due to thedifferences in pulp and papermaking process, the different color is formatted.Whiteness is one of the most important optical properties of paper. When lightstrikes the paper, the reflection and refraction and scattering will be occurred.The paper’s optical property is determined by the light’s amount of absorptionphenomenon under certain conditions.The whiteness of the paper is mainly determined by reflectance of lightirradiation on the specimen which is centered at the wavelength of457nmwhich is within the zone from380nm to510nm.This method does not considerthe visual characteristics of human eyes. Therefore, in the printing the L*a*b*value can be characterize the color of the paper, which can reflect the paper’swhiteness and coloring, but also is consistent with human color vision. When thepaper itself is partial color, the printing paper’s color is integrated color effect ofboth ink and paper, which will have some partial color. It is necessary to analyzepaper’s color based on manuscript, and correct the partial color by takingappropriate measures. In order to meet the trend of spectral color management,paper’s color can take spectral parameters. The reflectance in the visiblewavelength range can represent the paper and printing’s color, and the relationbetween the paper’s spectral reflectivity and the printing’s spectral reflectivity isstudied. The results show that the spectral reflectance of paper is linearly relatedwith the single color printing’s spectral reflectance, and the spectral reflectanceof paper isn’t linearly related with the multicolor printing’s spectral reflectance.At present, digital printing rapidly develops, especially the inkjet printing.Inkjet printing mainly uses water-based ink. In digital printing dot gainphenomenon exists. Inkjet printing’s dot gain mainly includes the optical dotgain and the physical dot gain. Optical dot gain is caused by the light’s physicalreaction inside the paper. The physical dot gain is mainly caused by inkspreading in the paper. In ink-jet printing, cyan ink absorbs the red light whose wavelength is from570nm to700nm and reflects the blue and green light whose wavelength isfrom400nm to570nm. High reflection zone of cyan ink is from400nm to570nm. The high reflection point is chosen at480nm, and the low reflection area isfrom570nm to700nm. The low reflection point is chosen at630nm.In ink-jet printing, magenta ink absorbs the green light whose wavelength isfrom500nm to600nm, and reflects the red light whose wavelength is from600nm to700nm, and reflects the blue light whose wavelength is from400nm to500nm. High reflection zone of magenta ink is from600nm to700nm and from400nm to500nm. The high reflection point is chosen at680nm, and the lowreflection area is from500nm to600nm. The low reflection point is chosen at530nm.In ink-jet printing, yellow ink absorbs the blue light whose wavelength isfrom400nm to500nm, and reflects the red light and green light whosewavelength is from500nm to700nm. High reflection zone of yellow ink isfrom500nm to700nm. The high reflection point is chosen at680nm, and thelow reflection area is from400nm to500nm. The low reflection point is chosenat430nm.Through the analysis of the spectral reflectance curve of yellow, magenta andcyan ink products, we can find the value that is the sum of the reflection at lowreflection point and the reflection at high reflection point devided by thedifference of the reflection at low reflection point and the reflection at highreflection point is close to the dot area. So the method can be used to predict thedot area value of cyan, magenta, yellow ink. In the study, the dot area value onthe different paper is analyzed. The paper is more cyan, cyan ink’s dot area valueis predicted bigger. The paper is more magenta, magenta ink’s dot area value ispredicted bigger. The paper is more yellow, yellow ink’s dot area value ispredicted bigger.The Yule Nelson spectral Neugebauer (YNSN) model is proposed todescribe the relationship between the spectral reflectance and print dot area value.Dot area can be predicted by measuring the spectral reflectance of the prints,which is an ideal model. In order to apply the YNSN model better, the revisedindex is needed. In the prediction of shallow color dot area, the spectral reflectance of paper’s inverse is modified index. The dot area percentage ispredicted by using the least square method. The experimental results show thatthe prediction accuracy is good.In the spectral color management of multicolor printing, the color’s spectralreflectance which is not in the profile and ink’s dot area value is necessary to beconverted. The process parameter is much, and the amount of calculation is large,and the difficulty is high. In the study, the color conversion using BP neuralnetwork is taken. The spectral is segmented in order to express spectralcharacterization of different colors. The reflectivity at the wavelengths of430nm,480nm,530nm,580nm,630nm,680nm is used as the input value, greatlyreducing the amount of training data, and this color model is called improvedconversion model based on BP color spectrum. In spectral color space modelbased on the Levenberg Marquardt (L-M) algorithm, the training function wastrainlm, after iterations, the root mean square error is less than0.1×10-3requirements.In order to find the color out of the gamut, the spectral reflectance curves’scharacteristics in monochrome, two color, three color printing is studied in orderto find the color gamut’s conversion method. In the spectral color reproduction,color gamut’s parameter is spectral reflectance curve which can represent thecolor gamut that is more convenient.In monochrome, two color, three color printing, ink’s spectral reflectancecurves is observed in order to find the characteristics of color gamut and find thepaper’s spectral gamut. The cyan ink’s peak is from420nm to560nm. The dotarea is smaller, the spectral reflectance at all wavelengths is more large,especially at the wavelength from580nm to730nm. The dot area’s difference isgreater, the spectral reflectance’s difference is greater. The spectral reflectancecurve is between the top curve whose dot area is zero and the bottom curvewhose dot area is100percent.The overprint color’s peak of cyan ink and the yellow ink appears at thewavelength from490nm to540nm. The spectral reflectance changes slightly atthe wavelength from630nm to730nm. When the cyan, magenta, yellow inkoverprint, the wavelength peak gradually moves forward with the magenta ink’sincreasing. The spectral reflectance decreases at the wavelength from380nm to 630nm, and the spectral reflectance’s reduction is largest at the wavelengthtrough. When magenta ink’s dot area value is constant, with the increasing ofyellow ink’s dot area value, the spectral reflectance decreases much at thewavelength from380nm to480nm, and spectral reflectance decreases slightly inother wavelengths.When cyan ink overprint with magenta ink, with the increasing of themagenta ink’s dot area, the peak turns small at the wavelength from380nm to560nm, and the trough is made at the wavelength from540nm to580nm, andthe reflectance is not changed at the wavelength from590nm to730nm.Therelationship between hue, lightness and saturation for spectral reflectance curvesis look for. It is necessary to determine whether the color is in the spectral colorgamut.If not, first determine it is what kinds of ink to overprint according to thespectral characteristics and find the color gamut. Then according to the printingthe color conversion method is chosen that is hue saturation or lightnesscompression or saturation compression, and the height, width and the position ofthe peak is determined. At last the nearest curve is found out to replace it.The gray balance data is studied in order to make up for the influence on thecolor performance of paper or ink layer density or dot enlargement and trappingefficiency of color reduction. At present, there is calculation method of graybalance data base on density and chromaticity, and there is not calculationmethod of gray balance data base on spectral reflectance parameters.Accordingto some basic knowledge of the gray balance, reflectance in the visiblewavelength range of cyan, magenta, yellow ink, black ink is measured and madecomparative analysis. BP neural network is trained by using Matlab software, theactual dot area value is got when ink gray balance is realized.更多还原