The Dish on Dots

pP: Why might a printer choose finer line rule AM screening over FM or transitional techniques?
AGFA: AM screens vary the size of the dot on an established grid or line-screen ruling to change the tonal value. The finer the grid, the higher the frequency or number of dots and the closer the rows of dots are to each other. Varying conditions of the prepress process and the types of presses being used limit the screen ruling. The printing process, therefore, determines the choice of a traditional AM screen ruling; it is not solely a decision of preference.
ARTWORK SYSTEMS: AM screens produce smoother results than FM screens. This is because uniform patterns (AM) appear smoother to the eye than random patterns (FM). At screens below 200 lpi, the human eye can actually see the dots as well as the overprint patterns formed when multiple AM screens are printed on top of one another. AM screens greater than 200 lpi have the potential for high-quality results. However, the higher the screen ruling, the more difficult conventional AM can be on press. Even at 250 lpi, a 50 percent dot is about 80µ in diameter and will carry about an 8u film of ink. Such screens have excessive dot gain, poor stability, and do not have the color saturation of FM screens.
ESKO-GRAPHICS: The AM grid works well as a visual concept. In certain areas, the grid pattern of dots in AM screening is much better than in FM. For example, FM screening rarely looks good on flesh tones and should be used only for highlights and shadows.
FUJI/ENOVATION: It’s a dot structure printers are comfortable with. If their processes can hold higher screen rulings, dot gain curves can be adjusted, and they could see an immediate impact on the quality of the piece without purchasing additional screening technology. Again, it’s all about the process! Higher screen rulings also narrow the process control window.
HEIDELBERG: The main advantage is that it is easier to make plates and easier to print.
KODAK: A finer AM screen could be an alternative in situations where an FM screen is not appropriate; for example, in gravure and flexographic printing.