Informative approach for estimation of paper uniformity influence on print quality

INFORMATIVE APPROACH for ESTIMATION OF Paper uniformity INFLUENCE ON print Quality

Dunaev D.V.

Department of automated control systems of technological processes

Saint-Petersburg technological university of plant polymers

Ivana Chernykh 4, Saint-Petersburg, 197101, RUSSIA

e-mail: dmdunaev@pochta.ru

Abstract

Paper unumiformity has been known as one of the most critical factors that affect quality of prints. From informative point of view paper is channel of information transmission from master to print, where its uniformity adds noise to friendly signal. In this report we propose a practical application of informative method characterizing the effects of paper ununiformity on print reproduction. The method provides us with a framework for estimation paper properties as its printability. We showed that paper of various formation qualities has various information capacities.

Introduction

Quality of polygraphic product depends mostly on preparation carried out on prepress processes, print techniques, equipment involved and material properties, such as either paper properties or ink used [1].

Screen print quality depends on print accuracy details. In general its value depends on paper uniformity.

Nonuniform paper gives mottled printing. This happens because of nonuniform ink penetration. The more uniform paper the less its resolving capacity. This leads to optical density variations and prints starlighting. The above mentioned results in undesired gross distortion and loss of information during it transfer from master to print.

The mathematical description of paper surface using mathematical formulation is complex therefore none of used estimation is objective. Each one of them describes only one-sided characteristics, whereas right estimation has to describe all paper surface features. Print quality estimations describe one-sided features also, whereas visual perception has integrated effect.

Furthermore subjective estimation with regard to evaluation print quality has psychological perception. Therefore issues about sharp estimation for instrumental measurements remain opened.

One of the main performance criterion for estimation of print papers quality is it convenience for information transfer, therefore in cases of either information encoding on paper or paper using in pattern recognition systems the demand of good print quality exists.

The tasks of this research are follows:

- practical application of informative method to estimate paper uniformity influence  on print quality;

- detection of relationship between information capacity and paper uniformity with regard to ink-jet printing.

Experimental

Paper serves as a carrier of optical information in the communication process. The negative base of two logarithm represents the definition of information:

where p_i is probability of an event.

For spatial information containing in grayscale print an event represents optically perceptible gray level (0…255 for monochrome printing).

The possibility of informative method application for estimation of paper uniformity influencing print quality described in [2].  The criterion used is the following:

where:

N is optically perceptible number of gray levels;

R_MAX and R_MIN  are the maximum and minimum reflectance as determined by the optical properties of the paper;

 is standard deviation of reflectances in print observed.

The expression (2) represents the signal-to-noise ratio. The difference (R_MAX - R_MIN) or the difference between their logarithmic values is the dynamic range. When printing, information can be stored in the reflectance or density area delimited by the dynamic range. Noise power is characterized by standard deviation () of reflectances in print observed. To a greater or less extent standard deviation is paper uniformity specified.

At macro level, reflectance representing the brightness value of paper determines R_MAX. A single-color printed image cannot be brighter than that excluding the possibility that the printing ink would be white or fluorescent. Reflectance distribution of paper surface controls the minimum reflectance R_MIN. This thinking uses the assumption that the only reflection from the surface is the surface reflection if there is a hypothetical layer of ink on the paper that totally absorbs light [2].