Informative approach for estimation of paper uniformity influence on print quality, страница 2

Consequently the increase of information capacity of paper is needed to increase the optically perceptible number of gray levels (N). It is achieved by dynamic range widening (R_max - R_min) and noise decreasing (), but these values are determined by uniformity of paper surface.

From this point of view informative method is feasible to consider paper as channel of information transmission from master to print, where paper uniformity adds noise to friendly signal.

Some patterns of printing papers differing by formation index were selected for investigation.

Formation index (Ind) is complex statistical indicator characterizing nonuniformity distribution of intensity levels of paper by light transmitted (Fig.1) [3]:

where: N_c is number of pixels having the same intensity as average intensity of all pixels I_c;

I_MAX  и I_MIN are maximum and minimum of paper intensity levels by transmitted light.

The higher and narrower histogram is the more uniform paper surface is.  The lower and wider histogram is the more paper surface is ununiform.

Patterns were reflective scanned then prints were made from 100% to 50% at intervals of 10%. Then print patterns were reflective scanned one more time.

Due to information processing from scanner we calculate (N) of each print area. Results of processing for two most deviated by formation index print patterns are represented in table. These relationships are represented at Fig.2. It is obvious that (N) differs by using papers of various formation qualities.

Conclusion

Results of investigations show that:

1) Application of informative method was used to estimate paper uniformity influence on print quality.

2) There is for sure a relation between paper uniformity and print quality. Moreover the influence of paper uniformity degree on discernible number of gray levels is really strong. It needs to be taken into consideration in papermaking processes in order to produce good quality product.

3) Optimum degree of screen-type pattern is 90%. At this level discernible number of gray levels has maximum peak.

4) At different screen-type patterns the informative capacity differs markedly by frequency modulation on papers with various formation indexes. It is really essential both to select grade of paper for printing and to tune conditions of print processes.

References

[1] L. A. Kozarovitskiy, Paper and ink in printing. Moscow: Kniga, 1965.

[2] P. Oittinen, H. Saarelma, Papermaking Science and Technology. Printing. Helsinki: Jyvaskyla, 2000.

[3] V. N. Leontev, “Paper ununiformity estimations and its influence on print quality”, Improvements in papermaking and printing, Bumdrevprom: Saint-Petersburg, 2004, pp. 119-126.