228: Thou shall understand the relationship between image resolution and halftone screens

Commentary All four-color process images are made from dots and are alternatively referred to as halftones. A photographic print isn’t made from dots and is known as a continuous-tone (contone) print. Screening is the term used to describe how a contone is converted to a halftone. The chosen print method and paper stock must be taken into account when selecting which halftone screen to use, with a higher value providing better print quality. A screen resolution of 150lpi (lines per inch) is standard for quality printing, while a newspaper will use a screen as low as 70lpi. The coarser screen will actually help prevent individual dots merging together when the ink spreads through the more absorbent newsprint. The relationship between image resolution and screen resolution is simple enough in that image resolution should be about twice that of the screen used, hence the industry standard of 300ppi and 150lpi. There’s some leeway in the equation. S....TS