allow a pc to convert a picture or object into digital code
that allows the computer to display and use an image. A scanner's
sophistication is the ability to translate an unlimited number
of analog voltage levels to digital values. The computer is
not able to use graphics unless they are in a form that they
can understand. The scanner takes the information it sees
on a page and converts into code that the computer can use.
A picture once scanned can be edited, printed, or used in
an application. Scanners can come with specialized software
called optical character recognition (OCR). This software
can read text as printed or written. The information can then
be manipulated in the computer.
Note: A feature of the scanner is the resolution.
This is how sharp and detailed the scanner can read. Scanners
are measured in dots per inch. The higher the resolution,
the more the memory that is required to scan the file. The
bigger the file that is produced. Larger files take longer
scanning time. If a file is big and you need to fit it on
a diskette, you may run into a problem storing it unless you
store it to the hard drive or another high capacity drive.
Therefore, if you are wanting to produce a file for screen
output, you should scan at 72 dpi because that the best resolution
that the monitor can display. It is the same of the printed
output. If you only have a 300 dpi printer, do not scan the
file at a higher resolution since the printer will only print
it at that resolution.
ScannerSheet-fed scanners have mechanical rollers that move
the paper past the scan head.
Flatbed ScannerFlatbed Scanners have a glass window where
the item to be scanned is placed on top of a while the head
moves past the item. This method is similar to a xerox machine.
Hand Held ScannersHand held scanners are small, portable scanners
that depend on a human operator to move the head across the
the object or image to be scanned. .
Color vs Grayscale
Scale: Using black and white and shades of gray, the scanner
is able to translate the image into gray scales. Why would
you use a gray scale scanner? If you plan to print on a black
and white printer, it is most cost effective since color ink
is so expensive. Text is best done on a grayscale scanner.
A color scanner scans images in red, blue, and green shades.
This scanner is more expensive in terms of final print output
. A color scanner usually costs more than a gray scale scanner.
If you plan on doing presentation work, work with color photographs,
or any sort of task that requires a color output, then use
a color scanner. With this scanner you can also choose options
of scanning such as line art (scanning the image only in black
or white), grayscale (black, white, and shades of gray, or
color (shades of red, blue, and green).
a Flatbed Scanner Works
A light source underneath the picture or document illuminates
the image. Spaces white or blank reflect more light than do
inked and colored areas.
2: A motor moves the scan head underneath the page. when the
scanhead is moving it captures light that was reflected from
individual areas of the page about 1/90,000 of an inch
3: Light from this page is bounced through an intricate system
of mirrors that must continually pivot to keep the light beams
aligned with a lens.
4: A lens focuses the beams of light into light sensitive
diodes that translate the amount of light into an electric
current. The amount of the current depends on the amount of
light reflected, the greater the amount of light reflected
the greater the current.
5: The analog to to digital (A-D) converter stores each analog
reading of voltage as a digital pixel representing either
a black or white area. Scanners that are more sophisticated
can translate the voltage into shades of gray. In a color
scanner, the scan head makes 3 passes under the image and
the light on each pass is directed through a red, green or
blue filter before it strikes the original image.
6: The digital information is sent to the pc where it is translated
into a format that a graphics program can read.
How A Hand-Held Scanner Works
On the majority of handheld scanners when you press the scan
button a light-emitting diode (sometimes called a LED) illuminates
the image below the scanner. An inverted, angled mirror that
sits right above the scanner's window reflects the image onto
a lens in the back of the scanner.
2: The lens focuses a single line of the image onto a CCD
(known as a charge coupled device), which is a component designed
to detect subtle changes of voltage. As the light shines onto
sever rows of light detectors located on the CCD, each registers
the amount of light as a voltage level that equals to black,white
3: Special analog chips receive light voltage generated by
the CCD for gamma correction. This process enhances the black
tones into an image that is that the eye will have be able
to recognize the shades of the image easier.
4: The line of the image now is moved to the analog-digital
converter. In a gray scale scanner, the converter assigns
8 bits to each pixel, or 256 shades of gray.
5: As the disk turns, a light shines through the slits and
is detected by a photomicrosensor on the other side of the
disk. When light strikes the sensor it throws a switch that
sends a signal to the A-D converter. This signal tells the
converter to send the line of bit generated to the computer.
Then the converter clears itself of the old data.
6. The computer then moves to the next line.