These techniques should only be used if you’re in a bind. For example, if you’ve
scanned or downloaded a small image and need to increase its resolution so that
you can print it at a much larger size.Printing Press Output and Resolution
At some point, your images might end up in the printing press. Printing presses use
a plate containing a special screen to print images. This system relies on dots as
well, but the term used for printing presses is line screen, or lines per inch (lpi).
Lines per inch is the number of dots that appear on a halftone screen (see Figure
12.7). A halftone screen is a plate containing a uniform pattern of transparent holes
in an opaque background. The plate is usually metal, and is etched by a laser and
chemicals. The plate is put on a massive roller and coated with ink on every revolu-
tion. The paper travels through at high speed and receives the ink. This line screen
enables printing presses, which use solid colors of ink, to produce continuous tone
images.188 ABSOLUTE BEGINNER’S GUIDE TODIGITAL PHOTOGRAPHY
FIGURE 12.7
A photo from a
magazine show-
ing the line
screen used by
the printer.