Flatbed scanners are the best-known and largest
selling scanner type, and with good reason. They're versatile,
easy to operate, and widely available. Their popularity for
Web publishing has opened up a huge market. At the other end, professional
units for the color graphics market now rival drum scanners in
quality. All use the same basic technology, in which a light
sensor (generally a CCD) and a light source, both mounted on a
moving arm, sweep past the stationary document on a glass
platen. Automatic document handlers (ADH) are available on
some models, and can increase throughput and lessen operator
fatigue for sets of uniform documents in reasonably good
condition. A specialized variant of the flatbed scanner is the
overhead book scanner, in which the scanner's light source,
sensor array and optics are moved to an overhead arm assembly
under which a bound volume can be placed face up for scanning.
Sheet feed Scanners
Sheet feed scanners use the same basic technology as flatbeds,
but maximize throughput, usually at the expense of quality.
Generally designed for high-volume business environments, they
typically scan in black and white or gray scale at relatively
low resolutions. Documents are expected to be of uniform size
and sturdy enough to endure fairly rough handling, although
the transport mechanisms on some newer models reduces the
stress. Using roller, belt, drum, or vacuum transport, the
light sensor and light source remain stationary while the
document is moved past. An important subclass of sheet feed
scanners are upright models specifically designed for oversize
documents such as maps and architectural drawings.
Drum scanners produce the highest resolution
and highest quality scans of any scanner type.
In addition to the higher cost, drum scanners are slow, not suitable
for brittle documents and require a high level of operator
skill. Thus they are typically found in service bureaus that
cater to the color pre-press market.
Microfilm scanners are highly specialized
devices for digitizing roll film, fiche, and aperture cards.
Slide scanners are used to digitize existing
slide libraries as well as photo intermediates of
3-dimensional objects and documents that are not well-suited
for direct scanning, though more and more such objects will be
captured directly by digital camera. The use of transparent
media generally delivers an image with good dynamic range, but
depending on the size of the original, the resolution may be
insufficient for some needs.
Digital cameras combine a scanner with camera
optics to form a versatile tool that can produce superior
quality images. Though slower and more difficult to use than
flatbed scanners, digital cameras are adaptable to a wide
array of documents and objects. Digital camera
technology continues to improve, helped along by the growing
3D scanners are a fast way of
placing the measurements of an object onto the computer in an
detailed manner, resulting in what is known as 3D scan data.
Generally, the 3D scan data is represented with an accurate
digital scale model or a 3D graphical rendering. Once the data is on the computer, all of the
physical dimensions of the object can be taken, such as length, width,
size, location, surface area, etc.