Imaging and Color - The Graphic Design: Reference and Specification - page 19

f i n d i n g t h e b e s t s c a n n i n g r e s o l u t i o n
When you select a dpi for an image scan, you are designating the amount of image informa-
tion your scanner will capture—the higher the dpi, the more image data, or potential for clarity
your image file will have. Although scanning at a high dpi may ensure that every detail of your
image will be captured, the large size of high-resolution image files makes them cumbersome
to work with. Scanning at optimum resolution means getting the best image clarity and repro-
duction you can achieve with the lowest possible file size or dpi.

To choose the best scanning resolution for an image, start with your image output in mind:

• Digital display —Anything that will be dis-
played on a computer monitor or as part
of a digital presentation (PowerPoint, etc)
should be scanned at 72 dpi. This is the
best image reproduction you can achieve,
because a computer monitor's resolution
is just 72 dpi. .

• Print output for commercial printers —
The scanning resolution for a continuous
tone image such as photograph or illus-
tration that will be converted to a halftone
should be dictated by the lpi of your half-
tone screen. When scanning for halftone
output, the scanning resolution for your
image should be a dpi that is double
the lpi of your line screen. For example,
a photograph reproduced with a 150 lpi
halftone screen (standard for a magazine)
should be scanned at 300 dpi. However,
if the same photograph appears in a
newspaper (where halftone screens are
generally 85 lpi), the scanning dpi should
be 170 dpi.

• Print output for studio printers —
Scanning for print reproduction depends
on your output device. A 300 dpi studio
printer requires images scanned at 300
dpi for optimum clarity. Let this 300 dpi
rule of thumb be your guide when scan-
ning line art and continuous-tone imagery
for studio output.

s c a l i n g a n i m ag e
Beyond output, the other consideration to keep in mind when scanning an image is scale.
Reflective art that is reduced will gain clarity, whereas, reflective art that is enlarged will
lose it. For instance, when a 300 dpi scanned image is enlarged by 200 percent double
its original size), its image resolution is reduced to 150 dpi. If the same image is reduced
by 50 percent, its resolution becomes 600 dpi. It's best to scale your image to a size that
is close to the size it will appear in its final destination, and then pick the appropriate dpi.

When scaling an image, use this formula to arrive at the right percentage:

Size of your reduction or enlargement × 100 ÷ the size of your original = percentage.

Example: 8” image scaled to 4” ( 4 × 100 = 400 ÷ 8 = 50% )