Research On Printing Performance And Color Expression Controlling Based On Paper Whiteness

Paper whiteness was one of important influencing factors of theprinting quality which was paid more and more attention by printingand paper industry. The high quality requirements and preferences ofconsumers demanded higher paper whiteness for printing enterprises.Thus, in order to cater to consumer market, the papermaking enterpriseshad to keep improving the paper whiteness.For a long time, Negative impact brought by the paper with highwhiteness had been ignored, for instance, high whiteness paperproduction lead to high loading, high chemicals consumption, highenergy consumption and heavy environmental pollution. Meanwhile, theutilization of high whiteness papers would inevitably cause theproblems such as serious sense of high light stimulation and visualfatigue. To explore the effects of high paper whiteness on our vision, itcould provide a basison controlling the whiteness reasonably. In thispaper, it was used the methods of instruments test and human feelingexperiments toreveal the relationship between the whiteness with visualfatigue of humans. The correlation analysis method was employed toevaluate the correlation between whiteness with the quality parameterof printing product and it could judge the effect of whiteness on productquality. According to this, a suitable method for evaluating the qualityof printing product was proposed targeted. Moreover, it was studied theregularity between paper structure with color difference which lookedforward to open up a new way for improving the quality of printingproduct. The specific researches and results were as follow:The relationship between the whiteness with visual fatigue ofhumans was detected by the methods of instruments test and humanfeeling experiments. Instrumentstest was to gather the pupil dynamics characteristic values of human when the synthesis of the light sourcewas illuminate and that value was to judge the eyes physiologicalreaction conditions with the change of radiation source which wasmatch to the corresponding paper whiteness, to predict the condition ofhuman eye fatigue when facing the different whiteness of paper. Humanfeeling experiments were implemented by observing, inquiring andrecording the visual fatigue reaction situation when the subjects werereading different whiteness paper manuscripts in the same readingenvironment. Research results show that the higher the paper whitenesswas, the greater the pupil response amplitude of subjects were and theshorter the response latency was, so with the paper whiteness increased,the parasympathetic nerve excitability increased, and the incidence ofvisual fatigue increased. The higher the whiteness of reading literarybackground was, the more the number of subjects with visual fatiguewere, and the more visual fatigue phenomenon was. Therefore, with theincrease of paper whiteness, the human eye fatigue more easily tohappen, it should choose lower whiteness of papers when the mainpurpose on printing product was read.According to the characteristics of the experimental data, thecorrelation between sample data would adopt the Kendall correlationcoefficient and Spearman rank correlation coefficient to determine.Paper whiteness value, the field density, dot enlargement value,overprint rate, and color difference value were choose to be variables,and using SPSS software judged data correlation mining. The resultsshow that there was no regularity existing between paper whitenessvalue with field density, dot enlargement and overprint rate, while theluctuation of the color difference was obvious. The result of correlationcoefficient analysis and validate parameter verified that the paperwhiteness and color difference has significant negative correlationrelationship. As a consequence, low whiteness paper will affect theprinting color reproduction. If the lower whiteness paper would bewidely used, the printing mills should solve the problem of print colordifference firstly. There was a special ability in human brains that could put thevisual mechanisms together in dependently. However, this mechanismswere sensitive only for a certain part of frequency domain. Hence, thefilter was applied to simulate visual characteristics of human. Firstly, Itwas used the contrast sensitivity function as the convolution kernel tofilter for the images which simulated the working principle of visualsystem. Secondly, the CIELAB color difference model was introducedby color difference analysis and obtained the results. Lastly, it wasverified the evaluate method and eyes perception fit by the feelingexperiments of eyes. It was showed that the color difference evaluationmodel based on human visual features largely in line with the humaneye perception color difference’s result, this method was easy to use,had strong repeatability, and the evaluation results were more accurate.It can effectively evaluate color difference of printed product.Paper X ray diffraction crystallinity, surface roughness, andporosity structure were characterized by the X ray diffraction, atomicforce microscopy, and scanning electron microscopy and therelationships between structure and printed product were researchedfrom the angle of the optical function of paper. It was described that thelarger the crystallinity was, the smaller the paper printing colordifference was; the smaller the roughness was, the smaller the paperprinting color difference was; For the paper with more filling, therewere two optical interfaces (packing air and packing fiber opticalinterface), which changed the optical contact area, so the paper andpaper internal reflection light and scattering coefficient factor wouldchange accordingly, paper printing color difference also havecorresponding change. Forth is reason, paper enterprises could use therelationship of paper structure and the color difference to guide tooptimize process, adjust the paper structure, finally printing qualitycolor difference would achieve the goal.The input image was converted into three channels(R, G, B), theimage was managed with histogram equalization processing algorithmrespectively in the three channel. Then image was converted to YCrCb color space, the Y channel edge was extracted by using the Sobelalgorithm, suitable reference whiteness area was found in the edge area.After reference white area was found, color image was corrected withVon Kries color correction model. The research results showed that theinput image is histogram equalization in three channel, color differencewas improved, and image after color correction according to Von Kriescolor correction model was closer to nature. After the input image wascorrected by digital printer output to the lower degree white paper, anevaluation method based on human visual characteristics was evaluatedwith the original color, the color difference obviously decreased. Thismethod was helpful for improving the color difference of the lowerdegree whiteness paper.To sum up, this research demonstrated that the paper whitenessreally threatened to the human eye vision. It was suggested for theprinting enterprises to use the low whiteness of paper to produce theprinting products which were only for reading. And put forward thesolution of the low whiteness paper printing color difference problem.The results were beneficial to lead people understand the paperwhiteness correctly which would be good for eyesight protection. It hadprovided a theoretical reference for the wide use of the low whitenesspaper. Furthermore, there was also a realistic and positive significancefor promoting the paper and printing industry to save resources,achieving a low carbon economy as well as sustainable development.