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What to Look for Scanner
Resolution
There are two types of resolution, optical and interpolated;
the first is the most important. The optical resolution of a
scanner is measured in dots or pixels per inch (dpi or ppi).
More pixels mean better resolution and sharper image
quality. The number of pixels a scanner can generate is
based on how many CCDs are arranged horizontally and
vertically in the scan head. Remember one CCD produces one
pixel. Resolution is quoted both horizontally and vertically
(e.g. 600x300). When comparing resolutions always use the
smaller number. If you need to pick up fine details, small
fonts or complex lines or edges you'll want more optical
resolution.
The interpolated resolution for a scanner is always higher
than its optical resolution. To get interpolated resolution
the scanner takes the information from two true pixels and
using mathematical algorithms fills in a third pixel between
them. Since more pixels are being mathematically generated
the interpolated resolution is higher. Optical resolution is
a more reliable indicator of image quality so doesn’t be
fooled into mistaking interpolated resolution for optical
resolution. Higher interpolated resolution will be
sufficient if you just need to enlarge images.
An optical resolution of 300 dpi should be enough for the
average user. It will produce an image that will look good
on the web or printed out on an inkjet or laser printer.
Graphic artists who want to scan line art or images with
lots of detail will want to go up to 600 dpi. Only people
who are looking to buy a scanner for slides, negatives or
transparencies need 1200 dpi resolution. Such a high
resolution is needed to compensate for the small size of the
original.
Even if your printer has lower resolution than your scanner,
scanning at higher resolutions will produce better image
quality in the finished document. You want to scan at higher
resolution than what you'll print at because the image
quality degrades when you process the image with editing
software like PhotoShop. A scanner with a higher resolution
will also produce better images even at resolutions below
the maximum. For example, a 150 dpi scan from a 600 dpi
scanner looks better than the same scan from a 300 dpi
scanner.
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