Here’s how to calculate more precisely the required resolution for
gray scale or color on an electronic color printer or a printing press:
1. Find out the
lines per inch
of the printing method. This is
the measurement of resolution for high quality image
printing. Do not confuse it with dots per inch, which is not
an equivalent measurement.
2. Multiply the lines per inch by two to find the best scanning
resolution For example, for 175 lines per inch (a common
resolution for magazines and books), scan your image at
350 dpi (2 x 175 = 350).
For even smaller file sizes, try scanning at about 1.5 times the lines
per inch This may cause little or no perceptible loss of output quality.
Note:
For color or gray scale images, ignore the dpi (dots per inch) of your
printing device. Even though your service bureau may use an
imagesetter with a 2400 dpi resolution,
a
scan resolution of only 150
to 350 dpi will produce the highest quality gray-scale or color images
the imagesetter can print. Similarly, even though your laser printer
may have a 300 dpi resolution, a scan resolution
of
only 80 to 120 dpi
give the best quality gray scale images it can print.
Size or scale
This is usually expressed as a percentage. If you want your
printed image to be larger than the original, increase its size
with this setting. If you are not sure how large you want the
printed image, choose the
largest size you might use. You can
reduce the image size later with your software. (You can also
increase the size with your software, but you may lose some
quality.)
Note:
The size of the image on your monitor will probably be different from
the size
of
the image when you print it.
2-14 Scanner Basics
