Print Quality Measurements in Offset Lithography

An instrumental method that accounts for direct influences of ink/paper, ink/press and paper/press interactions on image quality of imprints has been presented. The method is based on general principles of optical information transfer and studies of the human perception of visual information. It utilizes the measurements of a contrast as a function of image's spatial frequencies. These measurements are performed using specifically designed targets and accomplished by a computer-driven densitometer with following data processing, so that the print quality is expressed by a number 0 < Q < 1. The method was applied to measure Q for a sheetfed four-color press. The ink film thickness and paper stock were variables in the study. The results show clear maxima of print quality that can be achieved for the given ink/paper/press combination.