Scanning Images for Printing - "Dots Per Inch" is there a difference?
 One of the most common problems found in commercial printing is the quality of the
printed product. Most often, this is impacted by quality of scanned
images and artwork provided by the customer to the commercial printer.
Scanned images can drastically increase the amount of time and disk space it
takes to save a file, as well as the amount of time it takes to print. The
amount of detail recorded by the scanner is measured in dots-per-inch (dpi). The
higher the resolution or dpi, the more detail in the image and the larger the
file size. When you include a scanned image in a file, you may want to
keep the following points in mind:
- Use the optimum scanning resolution to keep images from
getting unnecessarily large. Do this by matching the scanning resolution to
the capacity of the output device.
- If an image has more resolution than a printer can
print, the printer simply ignores the excess.
- The best scanning resolution is equal to 1.5 to two
times the number of lines per inch (lpi) of the printer.
The following information will help you select the optimum
scanning resolution.
- Monitors: 96 dpi output. Scan Images at 96 dpi.
- Laser Printers: 300 dpi output, lpi of 55-65. Scan Images at 120 dpi.
- Laser Printers: 600 dpi output, lpi of 65-85. Scan Images at 120 dpi.
- Ink Jet Printers: 300 dpi output, lpi of 50-60. Scan Images at 110 dpi.
- Dye Sub Printers: 300 dpi output, lpi of 55-70. Scan Images at 125 dpi.
- Commercial Offset Printing: 2450 dpi output, lpi of 133-150. Scan Images at 300 dpi.
You may also want to consider the following "rules of thumb."
Scan Images at an Appropriate Resolution
If you are scanning in color or grayscale, scan at no more than one-half the
resolution of your printer. Therefore, if your laser printer prints at 600 dpi,
scan at no more than 300 dpi.
If you are scanning in black and white, scan at no more than your printer
resolution, but make sure that your scanner is set to "black and
white" or "line art."
Scan Images at the Appropriate Color Depth
If your original artwork is in color, but you will only be printing to a black
and white printer, scan it in grayscale. If your original artwork is a black and
white line diagram, scan it in black and white.
Scan Images at the Appropriate Size
Use your scanning program to scale the original artwork. For example, if you are
scanning a 5-by-5-inch logo to place on a business card, use the scaling
controls in your scanner software to reduce it to around 20-percent
(1-by-1-inch). Then use the scaling commands in your Desktop Publishing software
to get the logo exactly the right size.
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