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BOOT CAMP 167 (22/03/01)
Scanners & Cameras Part 1
We've touched on scanners and digital still cameras on
several occasions in Boot Camp, but it is about time we took a more in-depth
look at this increasingly important, and now very affordable group of PC
peripherals. At first glance scanners and 'digicams' seem to have little in
common but they actually do the same job, namely provide a means of getting
images into a PC. Once there pictures can be manipulated in an almost limitless
number of ways, imported into documents, used to illustrate Internet web pages,
they can be sent to friends and relatives as email messages or printed out onto
paper. This week we'll concentrate on scanners, and look at some of the things
they can do.
After a printer a scanner is arguably one of the most useful,
and certainly the most versatile peripheral you can have. They're also one of
the cheapest, with prices for budget 'flatbed' models now down to as little as
£40, so what can they do for you?
Scanning is a fairly simple process, on most models the image
lies face down on a glass plate or 'platen'; on the other side a bar fitted with
a bright light and a row of tiny light sensitive devices, known as CCDs (charge
coupled devices), travels the length of the platen, turning light reflected from
the image into a stream of digital data. This is fed to the PC, usually via the
USB port though a few recent models have a FireWire connection and some older
models plug into to the PC's parallel printer port.
This is where is gets interesting. The data file created by
the scanner represents an image and it can be used in a number of different ways
by the utility software that is in included with virtually all scanners these
days.
Two of the most useful extras are photocopy and fax programs.
Photocopying simply involves printing out the scanned image, and don't forget
that image can just as easily be a page of text or a diagram. There's more, if
you have a colour printer a scanner turns your PC into a high quality colour
photocopier! True, PC photocopiers are not as fast as the real thing but if you
only need to run off a few copies every now and again they're perfectly
adequate, and a darn sight cheaper and more convenient than print shops or coin
operated machines.
As you probably know, with the right software you can send
text documents created on a PC with a modem directly to a fax machine. However,
unlike a proper fax machine, the PC fax facility can't send copies of documents
on paper, handwritten notes, diagrams or drawings. With a scanner connected to
your PC you can, and on some models you can fax in colour, a trick relatively
few stand-alone fax machines can manage.
If you thought that was clever then how about optical
character recognition? OCR is another software utility bundled with most
scanners that converts a scanned image of typewritten or printed copy into a
text file. In other words, you can turn a page of text it into a document that
can be read by your word processor. OCR software is now very efficient and can
cope with a wide range of printing styles and in some case, even neat
handwriting. Most programs make a few mistakes, and they can get confused if the
document is scrappy or printed on non-white, textured or patterned paper but
even the most basic OCR packages can achieve at least 95% accuracy (under
favourable conditions), which can mean a huge saving in time and effort if you
routinely transcribe or type up a lot of documents.
Scanning photographs – which is what most people buy a
scanner for initially -- -- is the most straightforward task of all. The scanner software will usually produce a
'bitmap' or 'JPEG' image file that can be viewed directly on most graphics
applications and used in word processors. Some scanners come with graphic
programs of their own, usually 'lite' versions of the well-known packages.
What should you look for when buying a scanner? There are
basically two types: stand-alone flatbed models, and 'multi-function machines'.
The latter is a printer that scans, and sometimes has faxing facilities as well.
They can be very convenient when space is at a premium, and you need a new
printer, but otherwise stand-alone models tend to a lot cheaper and usually much
more flexible. Most flatbeds can accommodate documents slightly larger than A4,
some models can be fitted with slide film adaptors and dedicated slide scanners
are also available.
In all cases the most important considerations are
resolution, which is a measure of how much fine detail the scanner can capture,
and colour depth, which determines how accurately it renders colours and shades.
Resolution is rated in dots per inch or 'dpi' and that is directly related to
the number of light sensitive elements on the scanning head. Needless to say the
more the merrier, but manufacturers can sometimes be a bit devious. The only
true measure is optical resolution and the current mid-market norm is 600 x 1200
dpi. A few budget models are rated at 300 x 600, which is fine for most
undemanding applications but it's worth paying a bit more for the extra quality.
However, you may well see some scanners with absurdly high resolution figures,
up to 9,600dpi in some cases. This is 'interpolated' resolution, a software
trick, where the scanner program guesses at what's in between each dot. There
tends to be less variation in colour depth, most models have 42-bit colour
sampling, which is fine for almost all uses, a few older and cheaper models have
36-bit colour, which may limit their use in critical graphics and photographic
applications.
Next week – Digital Still cameras
JARGON FILTER
BITMAP & JPEG
Types of image file, Bitmap (extension *.bmp) is a standard
Windows file format, very accurate but file sizes tend to be large. JPEG (Joint
Photographic Experts Group) files (extension *.jpg) are 'compressed' to make
them smaller and easier to manage and send as emails. Some detail and colour
information may be lost but the drop in quality is usually so small as to be
virtually unnoticeable.
FIREWIRE
High-speed serial data connection system used on some high
end PCs and laptops used for demanding video and graphics applications
FLATBED
Desktop scanner with horizontal (flat) picture/document
holder, usually covered by a hinged top
TOP TIP
It happens every year, usually in early May and running
through to June: we receive a flurry of letters from readers that have had their
PCs and modems zapped by lightning. Spring is the start of lightning season in
the UK, so be ready for it and take some simple precautions to protect your
equipment. Surge protector plugs or adaptors can filter out damaging mains
'spikes' when nearby power lines are hit. Better still unplug your PC until the
storm has passed. You can get lightning arrestors for your phone connections but
these are not going to be much use if the telephone pole outside your house is
hit so get into the habit of disconnecting your PC or modem's phone cable as
soon as you hear the first rumbles of thunder, or you are going to be out of the
house and storms are forecast. A range
of surge protection products can be found at:
www.maplin.co.uk and
http://www.keison.com/furse/furse00.htm
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