An investigation of solid ink density variation as determined by the acceptability of overprints in process color printing

In order to establish limits which are representative of the allowable variation in solid ink density (SID) of the single process colors, as determined by the allowable variability of their overprints, a study was conducted utilizing fourteen (14) experienced color observers selected from printing companies in the Greater Rochester area. Printed color patches, at the 70% tint level of cyan, magenta, yellow, red (M+Y) , green (Y+C) , blue (M+C) and three-color overprints (Y+M+C) , were shown to observers, individually. In each group, the observer was asked to accept or reject the patch when compared to the reference standard in that group. The solid ink density of the process color or colors, which created the patch, were measured to determine the allowable variation in SID for the single colors, two and three-color over prints . The findings indicate that there is greater allow able variation when comparing single colors alone than when comparing their overprints. The standard deviations (S), ranges (R) and (R) average ranges of the allow able variation in SID for the colors utilized were: (See Thesis for Table). These findings and others would indicate that present standards, usually assigned to good quality color printing, such as -0.05, are unrealistic and unnecessary. The ranges allowed by these experienced color observers were as much as 0.42. Other significant findings show that magenta-reds are preferred to yellow-reds and that overall, increases in the magenta solid ink density were allowed more than increases in the cyan SID. There is conclusive evidence to show that these observers accepted greater variation in lightness than in hue and therefore would not accept as much hue change as lightness change. There is further evidence to indicate that it is important to monitor the hue change in the three-color overprints and near neutral colors, since these observers failed to accept comparatively small changes in SID in this region. It is, therefore, appropriate that the pressman vary SID on the press to maintain consistency in the overprints. In conclusion, it may be stated that densitometric values have been established which represent the allowable variation in SID of the single colors. These values are representative of the levels of the process colors on the press and could be applied towards a more effective method of controlling process color printing at the press.