Digital Prints

the bed of the scanner. They don’t really cover the full width of the scanner but only a portion
of it because they receive the image focused by a lens. The 4800 refers to the other
dimension and is achieved, as with inkjets, by motor stepping (this is sometimes called
“hardware resolution”). It’s the lower number—the optical resolution—that counts. Film
and drum scanners also use dpi, but they usually only list one number such as 4000 dpi.
Many scanners also list an interpolated resolution, which is invariably a larger number. Here,
sophisticated software is used to add extra pixels where there were none before. However,
this is fudging the pixel data, and it should not be a consideration when weighing scanning
or scanner choices.
A certain amount of knowledge of how scanning resolution affects printing is necessary,
so to get to the heart of the matter, I’ve gone to the source: Wayne Fulton. Fulton is the
author of what I believe is the most understandable and helpful book on the entire subject:
A Few Scanning Tips, www.scantips.com. What follows in an interview format are
some of the most common scanning resolution questions and Fulton’s answers.
■ How do I choose a scanning resolution? You scan for the capability of your output device,
which means that you choose a scan resolution based strictly on the needs of the monitor
or printer that will display that image. For images viewed on computer (video) screens,
scan resolution merely determines image size. Since ppi and dpi both mean pixels per inch,
then if you scan a print of 6 inches at 100 dpi, you will create 600 pixels, which will display
on the screen as 600 pixels in size. If you scan a 1 inch print at 600 dpi, you still have
600 pixels. And those 600 pixels will still fill 600 pixels on any screen (although the width
of those pixels will depend on the type of screen).
Chapter 3 ■ Creating and Processing the Image 79
A scanner with a wide density range
will help pull details out of the top of
this banyan tree in South Florida.