Digital Prints

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Mastering Digital Printing
(For a much more complete look at determining the size, scale, and resolution of your digital
files—including the use of odd/even or integer resolution numbers, see Chapter 3.)
Printer Resolution
Pull on your tall boots because we’re now going to be wading in deep!
How capable is the printing device of reproducing the information in an image? You may
have the highest-resolution image imaginable, but if the printer isn’t able to output all the
fine details you’ve worked so hard on, you’ve wasted your time. There are two main types
of printer resolutions to be concerned about: addressable and apparent.
Addressable Resolution
Digital printers have to translate all those nebulous image pixels we learned about into real
dots of ink or spots of dyes. The number of different positions on the paper where the
printer is able to place the little dots per unit area is its addressable resolution. Think of it
Commercial LPI vs. DPI
Spatial resolution is a measure of how finely the image information is grouped to be reproduced or rendered by the output device. With the digital
imagesetters used in commercial printing, this is where the line screen (or screen frequency) comes into play.
Using the typical 150 lines per inch (lpi) as the assumption, the printing dots are arranged in rows that are placed 1/150” apart. The spatial resolution
is then 150 lpi. Now output the same image at 85 lpi, and you’ve lowered the spatial resolution (and reduced the detail of the image). See
Figure 2.6 for an exaggerated example.
How does lines-per-inch (lpi) relate to dots-per-inch (dpi)? A 150 lines-per-inch image will probably be output on a commercial imagesetter at
2,400 dots per inch. The addressable resolution of this device is, then, 2400 dpi; the spatial resolution is 150 lpi. The 2400 dots are used to print
the 150 lines.
Clear as mud, right?
10 lines per inch 150 lines per inch
Figure 2.6 Two spatial resolutions for the same image for offset printing.