Playing Fast and Loose with Scanner Specs

By M. David Stone  |  Posted 2008-02-08 Print this article Print

From DPI to dynamic range, manufacturers like to snow you with specs. Which ones really matter, and why?

Specsmanship is a time-honored game that marketing departments like to play. But there are times when they take the game so far that the specs don't mean very much. 

Consider, for example, these common scanner specs that are widely misused and widely misunderstood. 

DPI or PPI? 

References to scanner resolution are almost always in dots per inch (dpi). The better metric is pixels per inch (ppi). It's not that dpi is wrong, but that it's too easy to confuse with printer resolution. Saying you scanned at 600 ppi and printed at 1,200 dpi is clear. Saying you scanned at 600 dpi and printed at 1,200 dpi could mean you changed the image resolution.

Resolving Detail: The Missing Spec

Scanner resolution should tell you how well the scanner resolves detail. Unfortunately, it only tells you how many pixels are in the scanned image. If the optical system of a 600-ppi scanner is limited to resolving, say, 400 ppi, the real resolution is only 400 ppi.

Dynamic Range

Dynamic range, a measure of how many different shades a scanner can see between black and white, is related to color depth, and as with color depth, it's almost always based on theoretical capabilities rather than a measure of the actual dynamic range. Here again, though, almost any scanner will have sufficient dynamic range for anything but transparencies.


M. David Stone is an award-winning freelance writer and computer industry consultant with special areas of expertise in imaging technologies (including printers, monitors, large-screen displays, projectors, scanners, and digital cameras), storage (both magnetic and optical), and word processing. His 25 years of experience in writing about science and technology includes a nearly 20-year concentration on PC hardware and software. He also has a proven track record of making technical issues easy for non-technical readers to understand, while holding the interest of more knowledgeable readers. Writing credits include eight computer-related books, major contributions to four others, and more than 2,000 articles in national and worldwide computer and general interest publications. His two most recent books are The Underground Guide to Color Printers (Addison-Wesley, 1996) and Troubleshooting Your PC, (Microsoft Press, 2000, with co-author Alfred Poor).

Much of David's current writing is for PC Magazine, where he has been a frequent contributor since 1983 and a contributing editor since 1987. His work includes feature articles, special projects, reviews, and both hardware and software solutions for PC Magazine's Solutions columns. He also contributes to other magazines, including Wired. As Computers Editor at Science Digest from 1984 until the magazine stopped publication, he wrote both a monthly column and additional articles. His newspaper column on computers appeared in the Newark Star Ledger from 1995 through 1997.

Non-computer-related work includes the Project Data Book for NASA's Upper Atmosphere Research Satellite (written for GE's Astro-Space Division), and magazine articles and AV productions on subjects ranging from cosmology to ape language experiments. David also develops and writes testing scripts for leading computer magazines, including PC Magazine's PC Labs. His scripts have covered a wide range of subjects, including computers, scanners, printers, modems, word processors, fax modems, and communications software. He lives just outside of New York City, and considers himself a New Yorker at heart.


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