Are you scanning line art or text?
Line art, such as pen and ink
drawings, and high-contrast images with sharp edges or type, should
be scanned at the highest resolution possible. Text scans that will be
processed with character-recognition software should also be
scanned at high resolution for accurate translation.
What halftone screen frequency will be used for printing?
For
continuous-tone images (photographs), a common rule of thumb is to
scan at a resolution of 1.5 or at most 2 times the screen frequency.
For example, for offset printing on newsprint at a screen frequency of
85 lines per inch (lpi), an image should be scanned at 128 to 170 ppi.
For images printed at 133 lpi, scanning resolution should be 200 to
266 ppi.
Talk with service bureaus and commercial printers about the screen
frequency used for your projects. With this information, you can let
Canvas calculate the optimal resolution for an image. See Resam-
pling and sharpening images on page 32.645.
Will the final image be smaller or larger than the original?
If
you need to enlarge the image, you should scan it at a higher resolu-
tion to retain the most information when you resize it. If you will
reduce the size of the image, you can scan it at a lower resolution.
Tip
Because resizing tends to
blur an image, you can use
the Unsharp Mask filter to
sharpen it. For more informa-
tion, see Sharpen filters on
page 34.702.
About digital images and
resolution
Digital images, also known as
raster and paint images, are
composed of tiny square pix-
els.
The number of pixels that fit in
a linear inch or centimeter is
the image resolution. The reso-
lution indicates how much
information is in the image,
independent of the resolution
used to display the image on
screen or to print it.
Low-resolution images have
larger pixels and look more
jagged than high-resolution
images. However, while high-
resolution images look
smoother, they also require
more memory and disk space.
Vector
72 ppi
300 ppi
600 ppi