Specifications

SCANNERS
INTRODUCTION to SCANNERS
SCANNERS
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Flatbed Scanners
The most popular type of scanner is the
ubiquitous flatbed scanner. Similar in
size and appearance to a small
photocopier, flatbed scanners
have a large rectangular
base, a glass platen
scanning area, and a
hinged door or flap that
holds the document flat
(face-down) on the glass
during the scanning process. It also
prevents unwanted light from leaking in during the scan.
Flatbeds offer easy setup and the most extensive features for the money. And
although most flatbeds are used for scanning reflective art, you can literally
scan anything that’s placed on the surface plate. That includes text docu-
ments, flat artwork, drawings, transparencies, even three-dimensional objects.
Flatbed scanners can be broken up into three basic categories:
Entry-level flatbed scanners usually feature a 8-1/2 x 11˝ scanning area, 600
dpi scanning ability (often interpolated via software to 1200 or 2400 “dpi”),
8- to 10-bits per color channel, and very low cost. They also usually come
bundled with an assortment of software for touching up photos.
Mid-level flatbed scanners are targeted toward a more professional market
and they differ mainly on a few key specifications and the type of software
bundled. Typically mid-level flatbed scanner will scan at 600 to1200 dpi and
10- to 12-bits per color for significantly higher quality scans. Some mid-level
scanners may also offer a larger scanning area, and most will include soft-
ware like Photoshop or Elements.
High-end flatbed scanners are positioned as alternatives to drum scanners.
They offer features that professionals demand, such as noise-free design,
large scanning area, high dynamic range, and high resolution. Although not
nearly as expensive as drum scanners, they do cost more than the mid-range
scanners.
The heart of any digital darkroom is the scanner. Available in different variations, scanners are the fastest, easiest and
depending on features, the most economical way to scan your film, prints, art, documents or small objects directly into your
computer. What type of scanner you need will depend on your application. The main distinction between them is how and
what they scan. Do you want to scan photos for posting on the web or for a brochure. Do you want to scan prints, slides or
both. But regardless of how you plan to use the scanner, they are all functionally the same. They use a light source to reflect
the image onto a mirror, and the mirror reflects that image to the camera through a lens. Then, the light/color sensitive pix-
els behind the camera translate the image into digital data and then sends that data to a computer. There, you can save the
image as a file, view it, print it, or edit it with a photo editing software—and then print it.
Flatbeds are convenient for scanning 3-D objects (such as books), can be very compact, and can scan a range of sizes. All
of them scan reflective material (i.e. non-see-through) as well as transparent material (adapter may be required). A sheetfed
scanner is strictly for reflective material, and feeds the sheets through the scanner past the image sensor. They are very com-
pact and good for someone who is looking to scan just documents. Film scanners are used only for scanning negatives and
slides (most also accommodate APS film). They're compact, and usually come with holders to help load the film. With a
photo scanner, you have a small scanner equipped to scan printed photos, and sometimes negatives and slides as well.
Inside the Scanner
At the core of the scanner is the scan head, which
contains a collection of CCD sensors. Similar to the
arrays in digital still cameras, the sensors measure
the amount of light reflected off or transmitted
through, a scanned image (film, photo or slide). The
information is then converted into electrical impulses
by a process known as analog-to-digital (A/D) conver-
sion and then reconstructed into a representation of
the image and projected onto the computer's monitor
(where it can now be manipulated, transmitted or
printed). An image is captured either by passing over
the sensors, by the sensors passing over the image or
by prisms or mirrors reflecting the object onto the
sensors. The first method, used by drum scanners
produces the best final image—the sensors don’t
move and are therefore very accurate (but much
more expensive). The second and third methods are
actually quite similar and are used by most scanners
(final output depends on the individual scanner).
CCDs like film, need to be exposed to absorb light and
capture the picture. More light as the scanner makes
a pass over the target makes the scanner’s CCDs
expose faster and speeds up the scan process. A belt
or a screw drive moves the head along the length of
image so the sensors can scan it. More precise motors
and faster drives result in shorter scan times.
A scanner with a speedy head and bright lamp is still
no good if it can’t quickly move images from the
scanner to your computer. Scanners offer either USB,
SCSI or Firewire (IEEE1394) connections with Firewire-
enabled scanners being the fastest.