so it's 2:00 a.m. and you're laying
alone on your couch watching reruns and
suddenly your phone lines up with a
message from a friend who needs a copy
of a very important document that is
sitting on your cheeto dust covered
coffee table for some reason so you're
going to take a picture of it with your
phone but you realize your crappy
built-in phone camera and the poor
lighting from the dingy bare bulb
hanging from the ceiling just aren't
cutting it so decisively you dash to
your PC and use your flatbed scanner and
as you sit there listening to the
whirling of the scanning mechanism and
pondering how your life got to this
point you find yourself asking how the
heck do these things work anyway great
question your typical scanner uses
something called a charge-coupled device
or CCD to determine what's on the page
the main idea here being that the CCD
can convert light into an electrical
charge which it then sends to your
computer as digital data so when you
start scanning a document that bright
light you see coming from inside
typically from either a xenon lamp or a
cold cathode which as you may know is
similar to what people use in PC case
lighting a few years back
it's the sheet of paper and reflected
back to a series of mirrors underneath
the glass surface and then focused by a
lens onto an array of CCD sensors since
darker areas of the page containing
things like text and clipart
will reflect less light in the blank
usually white areas the CCD array will
see these differences which will show up
as an accurate image of your document on
your computer screen if you've ever had
a scan of something bulky and had to
leave the lid open a little bit you'll
have noticed the scan is black in areas
that aren't covered by anything this is
because nothing's there to reflect the
light though modern software is often
smart enough to crop these areas out for
you CCD rates are also what determinate
scanners true resolution the more
sensors in the array the more points of
light it can capture and the more pixels
it can send to your computer if you're
in the market for a scanner make sure to
check that the resolution on the spec
sheet is the hardware resolution that
reflects the true
abilities of the CCD array not some fake
number achieved through software
trickery like interpolation that uses
average values of nearby pixels to
approximate a higher pixel count image
but what about color scanning this uses
additional lenses and built-in color
filters to separate the scan into red
blue and green versions which are then
processed to determine what the actual
colors of your original document are
although this is usually done with just
one pass of the scanner some older
models lack these additional lenses and
so need multiple passes to complete a
color scan which is why they were much
slower in color mode but not every
consumer level scanner works this way
there are also flatbeds that use
something called a contact image sensor
or CIS instead of these C CDs these are
simpler and construction use an array of
LEDs to shine light on the document so
an image sensor can essentially take a
snapshot of it like you were trying to
do on the table with your cell phone but
better
although the scans from the CIS are
typically lower quality than CCD
scanners CIS is a cheaper more
lightweight and more efficient
technology so you'll find it in a lot of
small portable scanners that can be
powered solely from a USB port instead
of requiring a wall outlet of course
there are other types of scanners out
there such as expensive drum scanners
with high dynamic range for professional
applications as well as 3d scanners
which you can learn more about right up
here but hopefully this episode has
given you a little insight into how your
scanner at home works and let us know
down in the comments down below if you'd
like to see a future episode on what
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like a drum scanner
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