from THE KODAK WORKSHOP SERIES: DIGITAL PHOTOGRAPHY
by Jenni Bidner. Copyright (c) Jenni Bidner, 2000. Published by Silver
(New York). Used by arrangement with Silver Pixel Press (New York).
Once you’ve decided on the type of scanner you’re interested
in, it’s time to look
at the details. It’s tempting to randomly select one based entirely
on the price
you have in mind. But unless you’re lucky, you won’t come
out with the best
scanner for your needs.
technological capabilities for scanners keep improving, what constitutes
"poor," "adequate," and "great" changes
along with the technological jumps. Hence to make a good purchase
decision, it becomes important to understand the underlying factors
that differentiate one scanner from another..
Optical resolution is often the lead specification in scanner advertisements.
After all, it’s usually the first concern—as well as one
of the more confusing factors—for newcomers. If it were the
only factor (or even the most reliable clue) as to how the scanner
will perform, then shopping for a scanner would take about as long
as it takes to dial a phone. It is, however, a good start.
resolution is measured in dots per inch (dpi), and the higher the
resolution the scanner offers; the larger you can successfully enlarge
your scan for any given application.
to decide at what dpi you need to scan your originals, you have to
think ahead to your end application. A 300 dpi flatbed scanner isn’t
what you need if you have professional publishing aspirations, unless
you’re planning to do a pocketsize book with tiny pictures.
But it’s great if you just want a scanner for fun and games—
like e-mailing pictures, small output to an ink-jet or other color
printer, children’s artwork, or optical character recognition
(which only requires 250 dpi or so). A 2400 dpi unit would be overkill
in this case. However, if you hope to manipulate your digital images,
output them, and get photo-realistic quality prints of a reasonable
going to need more powerful optical resolution (not to mention 24-bit
color or better). Likewise, the successful scanning of line art (including
signatures) requires very high resolution scans to achieve smooth
lines without jagged edges.
Interpolated or Enhanced Resolution
One misleading specification is interpolated or enhanced resolution.
Interpolated resolution starts with a hardware optical scan at a lower
resolution, followed by a software guess at what the higher interpolated
resolution should look like. In other words, it bumps up the dpi and
estimates the color of the added pixels. Some software guesses are
better than others. Regardless, it’s always better to have the
real optical reading, so judge your scanner by its optical claims.
Interpolation, however, can be good in another situation. When the
scanner is being used at less than its maximum dpi capability, some
scanners simply skip readings. For example, they just make every other
reading when scanning at 600 dpi on a 1200 dpi scanner. This enables
the scanning mechanism to cover the distance twice as fast and complete
the scan faster. However, most experts will agree that the best results
occur when the scanner takes the maximum reading (1200 dpi) and then
uses its computing power to interpolate the data downward rather than
just drop every other or every third pixel. This can yield smoother
tones and gradations. If your scanner can’t achieve this, for
top-quality work scan at the maximum setting and then use a professional
photo-editing software program to perform the downsizing. In the case
of halving the file size, side-by-side pixels would be evaluated to
come up with one new pixel value.
If your scanner doesn’t capture the subtle differentiations
between grays (in black-and-white scans) and between colors (in color
scans), then this information from the original is lost. This differentiation
ability is called color depth or bit depth. (See the second chapter
for more details on bits and bytes.).
In black-and-white photography, a print with 256 shades of gray looks
"photographic." It is
smooth and seamless to our eyes. But 256 colors (8-bit color) appear
posterized and fake when viewing a color image. The gradation of colors
is jumpy. If we give 256 steps (8 bits) to each of the RGB colors
that create the color palette, these colors can be mixed in 16.7 million
ways (256 x 256 x 256) to create 16.7 million color choices. Thus
24-bit color (8-bit red plus 8-bit green plus 8-bit blue) looks real
to us. With a 30-bit or greater system, the extra information can
be used for even more colors, or more likely, for advanced functions
like creating color information that can be exchanged for noise or
other damaged information bits to create a final, better 24-bit package.
In other words, it lets the scanner throw away bad or corrupted information,
leaving only the best 24-bit information. If you have a black-and-white
monitor, a black-and-white printer, and no aspirations of using your
digitized images in any color applications, an 8-bit system that delivers
256 shades of gray is more than adequate. But for more versatility,
you’ll probably want a color scanner, which can, of course,
also scan in black and white.
Being able to differentiate among subtle gradations of tones is a
much-overlooked factor that can have a huge effect on the printed
outcome. If you understand the science of photography, you know the
importance of the density range of films and printing papers. The
more tones the film or print can potentially show, the more realistic
the image will look. Professional conventional photographers still
work long and hard to pick the best film, lighting, exposure, and
developing combination to give them the tonal variations they hope
for in their images. Usually the goal is a large or long density range
that holds as much detail as possible in the highlights and shadows.
In the digital realm, we strive for the same thing, i.e., a higher
The best scanners are able to differentiate among subtle gradations
of tones, giving them a higher dynamic range, which is rated on a
logarithmic scale from 0.0 (low) to 4.0 (high). Itís no surprise that
these scanners are considerably more expensive than scanners with
a short dynamic range, which could have trouble giving you good scans
of transparencies or negatives that have high overall contrast. If
you need to reproduce the whole range of the original, with the ability
to distinguish among subtle tones in deep shadows or bright highlights,
hold out for a scanner that has a density range of 3.5 and above,
or use a service provider.
scanning color prints, you need not worry as much. Most color papers
have already flattened out the density range to about 3.0 before starting.
This is one of the reasons so many professionals use transparency
Drivers and Plug-Ins
and plug-ins are all about simplicity and, therefore, should not be
ignored. Drivers enable the scanner (or other peripherals) to communicate
with the computer. Scanning times claimed by the manufacturers may
not live up to your expectations if the driver is poor. Plug-ins allow
the scanner to be used with the most popular graphic design and photo
software, offering easy setup and integration.
new technology called Digital ICE (from Applied Science Fiction Inc.)
has recently been added to some scanners. Digital ICE automatically
removes surface and near-surface defects from scanned images without
altering the underlying image. This can save considerable time by
eliminating the need for painstaking retouching of dust spots and
scratches from your scanned negatives, transparencies, and photographic
prints. The newest generation can even restore colors on faded images,
Having said that, let's also say that you are now in position to get
some great pictures, like this:
your scanner choice may be more dependent on special accessories or
functions than anything else. If youíre going to scan the 20,000 slides
in your stock file, a dedicated desktop film scanner with an accessory
50-slide feeder could save you days of labor.
Likewise, the ability to easily batch images on a flatbed scanner
might be important. Almost any flatbed scanner will allow you to place
several at one time (or twenty 35mm slides if it has a transparency
adapter) simply because they fit on the glass. But can the software
treat them as separate images for easy saving as separate picture
files? Being able to save the scanned image in different picture file
formats might seem minor, but it can be a major headache if it doesnít
work. Make certain the scanning software (or plug-in for the photo
software) allows you to easily save your scanned images in the file
formats you most often use. It will save you time and eliminate translation
problems when later sharing the images.
Other considerations are specific to the occupation. Can the scanner
accommodate chest X-rays or mounted dental X-rays? Are there tethered
fiber-optic extensions for remote scanning? Can you program multiple
profiles for different scanning functions or multiple users? Read
your industry trade journals to find out about the latest and greatest
scanners for your particular field of expertise.
Line Art Black-and-white line art is any image or graphic made up
of two tonesó black and white or blue and white, etc. Your signature
is line art, as are many monochrome logos. Surprisingly, scanning
line art requires relatively high resolutions to achieve good results.
If you scan under 1200 dpi, your results may not be smooth and sharp.
Jagged edges or "jaggies" are the most common problem that occurs
from line art scanned at too low a resolution.
Other Factors Read the specifications carefully
before buying your scanner. As mentioned earlier, enhanced or interpolated
dpi can be misleading. Likewise, your scanner may not match the manufacturerís
claims if your computerís processing speeds are slow or if too little
computer RAM has been allocated to the scanner. Software bundling
should be factored into the price of your scanner only if you need
the software being offered. Note that many of the bundles are often
scaled down, less powerful versions of big-name software programs.
Popular bundling packages can include photo-editing software, OCR
software, and software that gives the scanner photocopying or fax
your scanner based mostly on what you plan to do, and then add in
a little extra power for expansion and growth. But the best advice
is not to drastically overbuy. You can always farm out the occasional
piece that canít be handled by the machine you select. At the rate
prices are falling and capabilities are increasing, the difference
in price between the scanner you need now and the higher-end scanner
might be the entire price of the better scanner in two years.
careful not to underestimate. The new generation of home-use computers
can easily handle FlashPix image files. Near-and true-photo-quality
printers are dropping in price so quickly that you may not be able
to resist adding one to your collection. These printers handle a lot
higher resolution and wider dynamic range than your older (and possibly
archaic) 300 dpi ink-jet. Even if you donít splurge for a photo-quality
printer, service providers can print your high-resolution digitally
enhanced photos with high-resolution printers, including units that
print onto silver-halide paper. So analyze what you honestly aspire
to do, as well as what you currently need to do.