Analyses of Frequency Modulated Screening on Newsprint

The fineness of an amplitude modulated (AM) screen is described by the screen rulings in lines per inch while a frequency modulated (FM) screen is measured by the microdot size in |m. The relationship between the microdot size in FM screen and the screen ruling in the AM halftone is implicit and not clear. This research uses the concept of the total border length per unit area on film as a common parameter to characterize both FM and AM screens on newsprint. By comparing the border length between FM screens to a reference AM screen, this study discovered that the border length of dots on film relates to the dot gain on press sheet. Thus, we are able to predict and compensate for the dot gain between AM and FM screens among the screens tested. In addition, by varying solid ink densities on a keyless newspaper press, we found that there is no significant color variation in a 42 |m FM screening and that of a 85 lpi AM screening.