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Scanned on a Slide Scanner
Scanned on a Flatbed Scanner
Slide VS. Flatbed
As you can see from this comparison, dedicated slide scanners can discern
differences in film types and are able to compensate for film differences
to acheive best quality.
Video Still |
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The most popular type of desktop scanner
is the ubiquitous flatbed scanner, so called because of its flat, glass
platen (or bed) which serves as both the scanning area and surface for
laying objects down to be scanned. Most flatbeds are used for scanning
reflective art.
Flatbed Scanners
Entry-level flatbed scanners generally share the
following specifications: 8-1/2" x 11" scanning area, 300 to 400 spi scanning
ability (often interpolated to 800, 1200, or 1600 "spi"), 8-bits per color
channel, and low cost. They often come bundled with powerful "value-added"
software such as Adobe Photoshop. These machines frequently offer excellent
price/performance ratio. Because there is fierce competition for this market,
at the time of this writing, the magic price for entry-level scanners seems
to be hovering around the $1000-$1200 mark.
Mid-level flatbed
scanners differ from their entry-level cousins in three important ways:
First they cost much more! Second, because they're targeted toward a more
professional market, they rarely come bundled with "value-added" software
such as Photoshop. Third, and most importantly, they have significantly
better specifications. For example, a typical mid-level flatbed scans at
600x1200 spi and 10-bits per color, resulting in scans of significantly
higher quality. Some mid-level scanners may also offer a larger scanning
area.
High-end flatbed
scanners are positioned as alternatives to drum scanners. They offer
features that professionals demand:a noise-free design, large scanning
area, high dynamic range, and high resolution. Expect to pay a premium
price of for these scanners. Mid-level scanners are increasingly taking
over this territory. Expect the lines to blur between mid-level and high-end
flatbeds in the near future.
Transparency Scanners
Multi-format transparency scanners allow you to
scan everything from 35mm slides all the way up to 4x5-in. transparencies.
These scanners are targeted to professionals only and thus cost quite a
bit. In fact, these high-end transparency scanners are muscling-in on the
once exclusive domain of drum scanners by offering more features, better
software, and faster scanning time.
Slide scanners cost
a lot more than the relatively inexpensive flatbed transparency option.
For those who may need only an occasional transparency scanned, a flatbed
with transparency adapter is the way to go. But if you scan a lot of transparencies,
then the only equipment that offers the best quality scans are dedicated
transparency scanners.
Video Digitizers
Today, most people use video digitizers for multimedia
purposes, especially in the creation of QuickTime movies. But that shouldn't
prevent you from occasionally using them to capture still images for print.
Video cameras utilize
the same digital CCD arrays found in flatbed scanners. These CCD arrays
produce an analog signal at (50 or 60 MHz) that either drives other analog
devices such as VCRs and television sets, or is captured onto video tape.
Video cameras technically aren't "scanners" in the truly digital sense
of the word. But, the analog video signal can be (re-)digitized using specialized
hardware and software. Video capture software is very similar to traditional
scanning software, while the hardware is usually a board that fits inside
your computer.
Although video cameras
provide an inexpensive way to get images into your computer, you should
be aware that the resolution will be low (only 640x480 pixels) and the
dynamic range will be low (usually less than 2.5). The color accuracy will
also be suspect. Nevertheless, video cameras are more than competent -
in fact, I've been using them for image capture in my own work since 1987.
Miscellaneous
A category unto itself, Leaf's Lumina camera/scanner
is a clever piece of equipment. Although it appears to be a digital camera,
the Lumina is actually a scanner, albeit an unusual one. It uses standard
Nikon bayonet lenses, which give it incredible flexibility. It scans at
2700 x 3400 and 36-bits deep for razor-sharp images and greater dynamic
range. At a reasonable $6900, the Lumina may obviate the need to buy both
a slide scanner and a flatbed scanner.
A pocket-sized device
from Trio Information Systems allows you to convert any fax machine
into a 1-bit scanner or printer using a standard fax-modem and proprietary
Trio software.
Talk about specialized
scanning! Pacific Crest offers a business card scanner that does
just what its name implies - it is dedicated to those people who need to
input and file tons of business cards! Who knows? It may be just for you.
PhotoCD
Okay, okay, PhotoCD isn't really a type of scanner,
but it is a useful way of getting images into your computer. All you need
is a CD ROM drive hooked up to your computer and a roll of film you'd like
to look at. Simply send the roll of film out to an authorized Kodak PhotoCD
developer and for about $1.00 to $3.00 per image you get your film developed
along with a CD-ROM containing your digitized images! Pretty neat, huh?
Plus CD-ROMs are a great way to keep your image files organized. The quality
of these scans is quite good and the proprietary PhotoCD format contains
several sizes of each individual image for various uses. The largest size,
2048 x3072 samples, is just large enough for a full-bleed 8 1/2" x 11"
image at 225 spi. (It also happens to be the same size as the propose HDTV
specification - coincidence?). You can probably get a better scan
by using a dedicated slide scanner (see below) and not compressing the
resulting image. However, if you don't want to buy a slide scanner and
learn how to use it, PhotoCD may be your best option.
Handheld Scanners
Hand scanners are useful for their portability and low
price (often one-third to a quarter of the cost of a flatbed scanner).
Hand scanners generally plug into a computer's printing port, as opposed
to a SCSI port, allowing them to be easily shared from workstation to workstation.
Many people find them ideal for use with a notebook or laptop. Unfortunately,
hand scanners are less accurate than flatbeds because they have weaker
light sources and often produce uneven scans - courtesy of the unsteadiness
of your hand or the surface you're standing on. Many hand scanners now
offer an alignment template to help guide you when scanning. At least one
manufacturer ships a motorized "self-propelled" unit to help stabilize
its scanner.
High-end hand scanners
offer 400 spi resolution and 24-bit color - allowing you to achieve reasonably
high-quality results. But their 4" to 5" wide scan head forces you to make
multiple passes to scan even average-sized documents. You'll need to use
the supplied stitching software to merge these partial scans back together
again - a time consuming task. Nonetheless, hand scanners are very popular
and are capable of high-quality, quick and easy, low-cost scans.
Drum Scanners
Professional color trade shops wouldn't think of using
anything less than a drum scanner for producing color separations for high-end
printing. Instead of using CCD technology, drum scanners use PMT (Photo
Multiplier Tube) technology for greater dynamic range and color accuracy.
They also cost an arm and a leg, Nevertheless, drum scanners offer features
not available to desktop scanners such as direct conversion to CMYK, auto
sharpening, batch scanning, greater dynamic range, and huge image scanning
areas. Ironically, most drum scanners don"t support preview mode - drum
scanner operators are more interested in numbers than what the see with
their eyes. Yet what truly sets drum scanners apart is their increased
productivity. Since the process of scanning to CMYK is automated, drum
scanners can produce more scans per hour than a desktop unit.
Digital Cameras
Digital cameras allow you to shoot three-dimensional
objects, much like a regular camera, except you don"t have to wait for
film developing and processing. Portable units are presently limited in
storage and image size. Studio-only units offer larger image size and dynamic
range, but require attachment to a host computer - hardly a portable solution.
In the future, high-resolution, high-quality, portable units will surely
come--they just aren't here now.
Previous incarnations
of "digital" cameras weren't really digital - they digitally sampled the
analog signal from a CCD as opposed to converting it to digital data. The
resulting data was then stored on floppy disk. The floppy disk then had
to be read by a special reader which converted the digital data back into
an analog signal which then had to be re-digitized again using a video
digitizer (see above) - what a mess!! As you might suspect, the quality
wasn't much to write home about, either.
Newer entry-level
digital cameras, like Apple's QuickTake, are truly digital, i.e. they keep
the signal (nearly) purely digital all the way from the CCD, to the floppy
disk, to the computer. The secret is that they use massive compression
of the digital data to get it all to fit on a floppy disk. Typically, these
devices save from 7 to 32 "frames" of digital data at up to 640x480 resolution,
and 24-bit depth. The quality is quite good - good enough for small (i.e.
2.5" x 3.5") reproductions in print, and certainly good enough for many
multimedia purposes.
More expensive mid-level
digital cameras such as Kodak's DCS 200 use higher resolution CCD arrays
(1024x1600) and high-capacity micro hard disks to store all that data.
The DCS 200 also uses compression to squeeze all that data onto the hard
disk. Optional features include digital modems for sending the images back
to a "home" office.
High-end digital
backs, such as the Leaf Digital Back (for Hasselblad and Mamiya), use even
higher resolution CCDs (2000x2000 or more), higher bit depth (12-bits/sample),
higher dynamic range, no compression, and high-speed cables to connect
the device directly to a computer, where the image is stored and manipulated.
Typically, these digital backs attach to a studio camera much like a Polaroid
back. The price of these high-end devices remains in the exclusive domain
of professional photographers., and as you might suspect, the quality is
quite good.
Fortunately, the
cost of these digital marvels is going down. I predict devices such as
these will eventually outsell traditional (film) cameras - and for good
reason. They are convenient, fast, quiet to operate, environmentally friendly,
and fun to use.
Stand - Alone Oversize Digitizers
For very large originals up to 40" wide (such as architectural/engineering
drawings) several manufacturers offer oversize, sheet-fed digitizers. These
unusual devices are somewhat related to the automatic document feeders
for flatbed scanners in that the original is pulled through the scanning
mechanism. They differ in that the scanner head is stationary, in fact,
they often bear a striking resemblance to CAD pen plotters. Because of
the large image area involved, and subsequent large file size, roll-fed
digitizers usually can only scan in line art and grayscale modes. Because
of their uniqueness and specialization, these devices are also quite expensive. |