If you know the exact image resolution desired for your onscreen image (for exam-
ple, 600 pixels wide × 400 pixels high), simply set the scanner software to scan
exactly that many pixels from the film or print.Scanning for Inkjet and Dye-Sublimation Output
For inkjet and dye-sublimation printers, a print looks reasonably sharp if it has 200
pixels per inch as a rule of thumb. Prints with more than 300 pixels per inch are
rarely useful; most people can’t see such fine detail. Between 200 and 270 pixels per
inch on the print is a good target number for prints that must look sharp.
How sharp does an image need to be? It depends on how it will be viewed. If an
image is smaller than 8×12 inches, it needs to look sharp, because people will view it
up close. You’ll not only need a scan that has enough samples per inch, but the film
or print you are scanning must be very sharp to begin with—otherwise the final
print will be unsharp, no matter how many samples per inch.
Some images don’t need to be sharp. Poster-sized images can have fewer pixels per
inch (25 to 100) because they are viewed from a distance (see Figure 6.5). The largest
images seen daily—outdoor billboards—may be printed with only two pixels per
inch. Images that are unsharp for deliberate aesthetic reasons do not need high-res-
olution scanning, but the pixels in the print must be small enough to avoid creating
a jagged look.78 ABSOLUTE BEGINNER’S GUIDE TODIGITAL PHOTOGRAPHY
FIGURE 6.5
As you scale up
an image, the
resolution (in
pixels per inch)
can go down.
This 13×19 inch
image was
printed at 150
ppi.