How Scanners Work
In a nutshell, a scanner is a device that analyzes
the surface of an image, printed text or an object and converts it
into a two-dimensional digital image. Scanners come in different
shapes and sizes depending on the intended use. The most common
scanner for home and offices today is the flatbed scanner. Handheld
scanners were briefly popular in the early 1990s but aren’t used
much anymore due to the difficulty in getting high quality images.
Film scanners are scanners that are used to scan positive or
negative film without the need of making any prints. Drum scanners
are the oldest and the most expensive of the four types of scanners
and are used for high end scanning.
Flatbed Scanners
 In most flatbed scanners, a bright light
illuminates the image while an array of capacitors moves across the
image, reading the entire area. The array used in flatbed scanners
is usually a CCD (charge-coupled device) array. When light hits one
of the CCD's in the array, the light photons free the electrons in
the semiconducting material, in effect creating a charge that's
directly proportional to the intensity of the light. This process is
repeated until the array reaches the end of the image and the
resulting sequence of charges is then digitized. Flatbed scanners
use a one dimensional array that moves across the surface of the
image instead of the two dimensional arrays that are used in digital
cameras. Flatbed scanners have become increasingly popular, even in
the photography industry as high end flatbed scanners are beginning
to rival the image quality of drum scanners at a much lower cost.
Flatbed scanners are available at a very wide price range starting
at around $50 for low end units and up to $50,000 for high end
units.
A newer technology that is rising in popularity in
the field of flatbed scanners is the use of Contact Image Sensors
(CIS). Instead of using mirrors and lenses found in a CCD scanner,
CIS scanners use red, green and blue LEDs to produce white light. A
single row of LED sensors are placed extremely close to the source
image for scanning. Since mirrors and lenses are not used, CIS
allows scanners to be more compact and portable. CIS scanners also
consume less power as a result of using LEDs instead of xenon or
cathode lights. One drawback to using CIS scanners is that the image
has to be extremely close to the glass due to the poor field of
focus. As a result, scanning the gutter of thick books can be
difficult.
Sheet Feed Scanners
 Sheet fed scanners are fundamentally the same as
flat-bed scanners, except that instead of laying the document to be
scanner flat on the imaging surface, it is fed through a roller
mechanism to pass it over a fixed imaging array. By there
name, it is clear that only individual sheets of paper are fed into
these scanners, so they do not offer the flexibility of flat-bed
scanners, but they do offer greater performance, since sheets feed
in automatically.
Sheet feeder mechanism are available for many
higher-end flat-bed scanners, and they are also built into about two
thirds of the All-In-One multifunction printers sold. They are
usually included in All-In-Ones to provide sheet fed fax capability.
Drum Scanners
 Drum Scanners, the first type of image scanners
ever invented, capture images using photomultiplier tubes (PMT). The
image to be scanned is mounted on an acrylic cylinder which rotates
at high speed in front of precision optics that deliver the image
information to the array of PMTs. Modern drum scanners use 3 PMTs,
which read red, green and blue. Even though few companies continue
to produce drum scanners, they are still in demand due to their
ability to produce high resolution scans. The obvious disadvantage
of drum scanners is that they aren’t as portable and easy to use as
flatbed scanners and take a long time to scan an image. The biggest
disadvantage though is price. New low end scanners start at around
$16,000 while high end scanners can cost $65,000 and above. On top
of that, you’ll have to buy the drums that cost $1,500 to $2,500
each, drum mounting stations for $1,500 to $3,000 and high end
scanning software for $1,500 to $4,000.
Film Scanners
 A film scanner is a scanner that directly scans
positive or negative film without the need for any intermediate
printmaking. Film scanners usually accept uncut film strips and scan
them using a CCD sensor. Most film scanners accept 35mm and 120 film
strips and individual slides. The advantage of using a dedicated
film scanner as opposed to a flatbed scanner is that the area to be
scanned is much smaller, allowing for higher resolution scans. Using
film scanners also has the advantage of being able to control
cropping and aspect ratio without changing the original film.
Dedicated film scanners will set you back around $100 for the entry
level models and may go up to $1900 on the professional quality
models.
Bar Code Scanners
 Bar
code scanners are devices used to scan encoded information usually
printed on product packaging. They fall into two different
categories: Hand Held, and Table or Surface Mounted (like at
your grocery store). In both cases they interface to your
computer in the same ways that other scanners do. These
scanners are designed to use a laser to optically scan the surface
of the object for a recognizable pattern, then capture that pattern,
and using software, convert it into an input string to the computer.
Types of bard code systems:
- Code 39
- Code 128
- UCC-128
- UPC-A
- UPC-E -EAN/JAN-8
- EAN/JAN-13
- Interleaved 2 of 5
- Codabar
- MSI Plessey
Business Card Scanners
 Business
card scanner, do what their name implies: scanning smaller single
piece documents. The also include recognition and contact
information management software, to capture that actual contact
information or other text contained on the card, and enter it
automatically into a database. The newer business card scanners scan
both color and black and white, and offer the ability to scan
business cards directly into popular software products, such as:
ACT!; Outlook; and Windows Contact Manager. They include accurate
and efficient OCR software allowing continuous scanning and
recognition of business cards. They are also TWAIN compatible,
so they can be used by any other TWAIN compatible scanning software.
Choosing Your Scanner
When choosing a scanner, you will have to
carefully examine what type of scanning you want to do and how much
you are willing to pay for it. To date, the best technology for
ultra high resolution scans is still the drum scanner. But because
of the disadvantages in price and expertise required to operate drum
scanners, many individuals and even graphics and print studios have
been shifting towards high end flatbed scanners.
Scanners & Windows Vista
As scanners decrease in cost, they are becoming
more disposable. As a result manufacturers are upgrading
scanner drivers less and less with each new version of Windows.
With the introduction of Windows Vista, this situation became most
obvious than ever. Many scanners that were designed for
Windows XP no longer work under Windows Vista, and no new driver is
available. The great irony is that almost all scanners use
industry standard software interfaces and TWAIN compatibility, yet
each still requires a unique driver. Therefore, before
upgrading to Windows Vista - if you love your scanner - be sure you
can still use it afterwards.
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