for preservation and manipulation that prints and
chemicals only could hint at. Yet despite these
advantages, each generation of reproduction di-
minishes the quality of the original photograph.
The contemporary desktop method of a digital
workflow includes the computer, scanner, and laser
writer. Industry-wide software programs and cross-
platform programs like QuarkXPress, Adobe Illus-
trator, and Adobe Photoshop allow the user to
scan, import, manipulate, save, layout, and print
images from a single desktop computer. Digitizing
and electronically archiving old photographs ex-
tends their longevity and freezes them in time,
while the original may continue to deteriorate.
The scanner, of which there are several types,
merely takes a picture of an image. Flatbed and
drum scanners dominate the marketplace. Most
consumers use a flatbed scanner, and professionals
use a drum scanner. Operating a flatbed scanner is
a simple matter: the lid is opened, and the flat
photograph is placed face down on the glass platen.
The scanner reads and turns the photograph into
digital information, thereby sending it through a
USB cable from scanner to computer program. The
software program used to scan and import the scan
is often referred to as TWAIN—the industry stan-
dard language that talks between scanner and com-
puter. The drum scanner, more expensive than
flatbed scanners, also captures more detail, which
is why they are more commonly found in profes-
sional applications, such as fine art presses.
Resolution
Resolution is the measurement of an image’s out-
put quality quantified by dots, lines per inch, or
pixels. Printers measure resolution in dots per inch
(DPI); computer monitors measure in pixels per
inch (PPI); halftones measure in lines per inch
(LPI); and scanners measure in samples per inch
(SPI). (In comparison, the normal human eye can
read at about 133 LPI.) Yet DPI and PPI are not
synonymous because it takes more dots to fill a
single pixel. Therefore, the ratio is not 1:1. Printers
are only capable of reproducing a small spectrum
of colors compared to the millions of colors found
in reality. Even given modern equipment’s ad-
vancements, photographers still cannot capture all
the colors of the world. Higher-quality printers,
however, offer better color reproduction given the
higher resolution of the image.
Images fall into either high resolution (high-res)
or low-resolution (low-res). For example, an image
with 300 DPI or higher is considered a high-res file
type suitable for various printing and publishing
applications. High-res scans are much less likely to
produce an image, whether viewed digitally or
printed out, that is grainy than a low-res file.
Low-res scans are used primarily for convenience
in sending files via the Internet or for insuring that
the image is not publication quality to discourage
unauthorized reproduction.
As discussed above, dots create an image; there-
fore, the quality of the scanner determines how
much information it will pick up. Scanner resolu-
tion fits into two categories: optical resolution and
interpolated (or digital resolution). Optical resolu-
tion measures what is actually evident, and inter-
polation artificially adds pixels to increase the
resolution. Not all scanners have interpolation
options. Usually this is an additional feature.
A scanner reads an image in samples per inch or
SPI. The more samples, the larger the file size. The
larger file size allows the user to make larger repro-
ductions. The general rule for the best resolution
when scanning an image is to scan the image at two
times the lines per screen than the image’s intended
printing. Thus generally a photograph should be
scanned at 300 dots per inch or DPI. A 300 DPI
photograph prints the same as a 600 DPI. This can
be applied only for scanning images though, where
knowing the substrate determines the lines per
inch. Images for posting on the Web, for example,
need at maximum a resolution of 72 DPI.Dot Control
There are three ways to control dots in reproducing
a photograph: screen frequency, screen angle, and
dot shape. A halftone is only one color (as is often
the case with line art), and continuous tone art is a
photograph that contains gradations of tone in
black, gray, and white. Halftones have no gradient
of color. The screen frequency is measured in LPI.
The more lines per inch, the less noticeable the white
space and the dots become. When discussing screen
frequency, there are the general guidelines for a
given substrate: 0 to 25 LPI for billboard, 25 to 55
LPI for silkscreen, 75 to 100 LPI for newsprint, 85
to 120 LPI for quick printers, 133 and up LPI for
commercial printers, and 150 to 175 LPI for glossy
magazines and fine art books.
Dot shapes are often circles, ovals, and squares,
particularly in photographs. Changing the shape of
the dot to a square, for example, changes and
increases the contrast in the image. Photo manip-
ulation software allows the user to change the
shape of the dot for desired effect.
The screen angle defines how the dots line up. The
angle ranges from 0 to 90.At45the human eyeSCANNING