 The magazine of the Melbourne PC User Group So, you want to buy a scanner? Jim Colbert colbert@melbpc.org.au |
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The other day, the following landed in my mail box as a result of a reply to
a question in a news group.
>
> You sound like you know what you
> are talking about. :-)
> So I've fooled you too :->
You've fooled me too, so much so that I'm going to ask if you'd like to write an article about scanning (any
aspect thereof, your choice).
Serves me right for putting in my 10 cents worth in a news group - so here goes.
To start with, bear in mind this is the lame leading the blind - e&oe - no correspondence will be entered
into (unless I feel like it) and the judge's decision is final - I appoint the judge.
First things first - You want to buy a scanner? - Why?
What you buy depends what on what you want to do with it (and don't say scan something - it's my article so I
control the jokes and sarcastic comments - OK?). Ask yourself what the finished product is going to be before
you even start thinking of a scanner because in scanning, the final output sets the input requirements.
If you want to scan paperwork for your fax modem or OCR text get the cheapest scanner you can - or just use
your own, or better still a friend's, hard copy fax machine to fax the paper to your computer and use the OCR
program in WinFax to convert it to text. Ideally this system will cost your friend $0.25 (for the phone call)
and you $0.00 which is much better than the hundreds or thousands of dollars you could end up forking out for
a scanner and software.
If you're after a bit more than that then read on - I can't guarantee to give you the right answer but at
least I hope I'll point you in the right direction.
There are various output targets and these set your basic scanner needs. Additionally what you're scanning
affects your scanner requirements and what's in between, i.e. your computer, may limit what you can do.
Remember that none of the processes will give you anything near photo quality so don't even dream about it.
When testing top quality lenses on cameras, resolution tests are in lines per millimetre - hundreds of them -
top quality colour glossy magazine printing is at about 6 lines per mm or 150 lpi.
Professional printing
Most professional print output is from an offset printing press which uses plates made from film supplied by
a pre-press bureau. Black and white printing uses one plate while colour uses four - cyan, magenta, yellow
and black. As mentioned, top printing quality in glossy magazines is around 150 lpi which doesn't exactly
relate to dpi but, very loosely, a full colour photo being scanned for printing at 150 lpi should have a
resolution of 600 dpi. The books recommend 300 dpi but, personally, I've found 600 seems to give a better,
cleaner final result - especially when working with colour separations.
For monochrome greyscale printing scanning at 300 dpi is fine.
I've included a few scans of the same subject at various resolutions - from 72 dpi, the lowest my scanner
will go, to 600 dpi. PC Update is printed at 133 lpi so you can see the difference or lack thereof.
Desktop printer
What's the resolution of your printer? If it's 300 dpi then anything scanned higher than 300 (for 1:1
reproduction) is a waste of resources. Additionally, even though your printer may print 600 or 1200 dpi there
may not be a discernible difference between a 300 dpi and 600 dpi scan when printed. Don't ask me why - I
don't know and anyway I'm short sighted and my glasses were probably dirty at the time.
Computer screen
If your screen resolution is set for 640 x 480 pixels it doesn't matter how high you scan - that's the
maximum number of pixels your screen will show. But what you see on the screen isn't necessarily what comes
out of the printer.
Web pages
The standard rule for images on Web pages is keep them small (in file size that is). Apart from the fact that
the picture is only going to be reproduced on a computer screen with next to no resolution, no-one wants to
sit around while a 20 MB picture file is dragged down from your site to their computer. Especially when they
discover it's a slightly out of focus picture of "me at my computer" and their ISP charges them by the
megabyte for bandwidth.
72 dpi is the recommended maximum for Web pages so ... who needs a 1200 dpi scanner for that?
Your computer
A brief note. Welcome to the world of graphics. If you're going to do any serious (or even not so serious)
photo manipulation go out and buy RAM. Then go out and buy more RAM - no matter what you have it's not
enough!
When I first started with graphics, in the days of Windows 3.11. I had 8 MB of RAM - a lot back then. Apart
from taking hours, the load on the machine made me an expert at rebuilding my system after it overloaded and
either kicked me straight back to the C: prompt in DOS. with no warning, or (horrors) left me looking at the
dread blinking cursor on a blank screen.
A standard postcard-size (6-inch x 4-inch) colour print scanned at 150 dpi creates a file of about 1.6 MB. At
300 dpi the same file is about 6.4 MB and at 600 dpi it leaps to 25 MB. There's a formula for this but the
software that comes with scanners usually shows you what the file size will be so forget it.
If you're going to play around with the image in a graphics manipulation packages you'll need 32 MB of RAM as
an absolute minimum - unless you feel like going and making a cup of coffee each time you change the
picture.
What are you going to scan?
Remember, however good the scanner and however good the printer and computer, GIGO still applies.
You can "fix up" an old torn photo a bit, get rid of specks, remove a pot belly, grow back hair and all those
wonderful things with modern software but if the original is no good the end product won't be much better.
Conversely, the better the source the better the end product. A scan of a photo from a creased-up page of the
newspaper will look like that no matter how good your scanner and, by the way, you could be sued for
copyright infringement as well.
If the input is going to be relatively low quality why waste your hard earned shekels on a $1000+ unit?
On the other hand if you're going to be scanning small but good quality pictures for printing in a much
larger size you'll need a scanner capable of high resolution. If you have a 6-inch x 4-inch photo that you
want to blow up on your computer and print out on A4 at 300 dpi you'll need to scan at a high enough
resolution to be able to increase the image size without the "real" resolution falling below 300 dpi. That
means you'll have to scan the original at about 600 dpi.
A brief comment on slide scanners at this point. If you're thinking of scanning your 35 mm slide collection
go and spend $1000 or more on a transparency scanner but don't expect it to do anything else (for 2.25-inch
square film spend $2500 to $3000). And by the way - you'd better buy a few more gig of hard disk or a 20 pack
of Zip disks or a CD-ROM burner. And you'll only be able to view them on your screen, unless you get a good
quality colour printer, like a top of the line Epson Photo or HP 600+ series or... Remember the ink for these
costs plenty and you use a lot of it, the special paper isn't cheap and, no matter what you do, the result
won't be anywhere like what you get - even from your local mini lab. And you can only use it for slides -
nothing else.
Flatbeds
On second thoughts get prints made when the film is developed and scan them on a flatbed.
(I'm going to get one of these machines myself when I've got the spare cash, because I can probably justify
it, but, unless you have a specific use for it and the spare cash - or someone who will pay you to use it,
forget it.)
So - you end up deciding on a flatbed. So buy the highest resolution you can afford? Wrong!
Quality in scanning comes from a number of things. A flatbed scanner works a bit like a photocopier. You put
a lovely sharp clear picture on a sheet of, hopefully clean, unscratched, glass and cover it so extraneous
light doesn't get in. A light source shines on the picture and a lens goes for a sort of meandering walk
taking a "picture" of whatever is on the glass. Usually the light source wanders along with the lens.
First off the lens should be pretty good quality. If you've ever seen the difference between photos taken
with a throw away plastic lens camera and a good quality TTL camera or by a camera like a Leica you'll know
what I mean. And it should be set up so it's focused right by the manufacturer - you can't do this
yourself.
Second, the light source should be good quality and stable, in a colour sense. Light has colour and, just to
depress you, the light from a lamp changes over the lamp's life. Household lamps are usually a dark yellow
light, halogens are a lighter yellow and sunlight is (relatively) white. The software with the scanner should
compensate for the colour cast from the scanner's light source but you don't want a light source that varies
all the time.
Third, the transport system, which controls the movement of the lens and light source, needs to be as stable
as possible - just like shooting with a camera at slow speed.
Unfortunately, none of the above seem to be mentioned in the specs for scanners. All they do is talk about
resolution. Only solution - try them all - ask lots of silly questions, ask your friends and neighbours ...
and pray.
Now you can worry about resolution. Figure out about how much resolution you will need, Double it, add $100
and you'll probably have a rough idea. This used to be easy when resolution was quoted as optical. Now watch
out. Remember when hi-fi power was watts RMS per channel and then some advertising geek came up with "total
music power" so they could pretend their unit was more powerful, when it wasn't? Well, something similar is
happening with scanners. There's optical resolution and interpolated resolution. The first is what counts.
The second is a method of the machine "imagining" what's in the spaces that it doesn't see and filling in the
blanks - nothing wrong and it works well at times but it's not real resolution.
And remember that a 300 dpi scanner with top quality components (lens, light source and transport) may give
much better scans than a 600 dpi scanner with poor quality innards.
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Other features?
Transparency adapters, to my mind and for what they cost, are a waste of money. They're not much good for
scanning 35mm slides or negatives (they're virtually useless since, even if the scan is OK, you're going to
have to blow it up enormously to get a usable image) and who wants to scan large size transparencies? It's
probably cheaper to get prints made from your film and scan them.
The super el cheapo one page scanners? Great idea back when (like last year). In view of the low cost of
flatbed scanners now, which will do books, fat things and all that, you might as well spend a few more bucks
for a flatbed.
I'd recommend a scanner with its own card, rather than one that uses your parallel port. They're a bit faster
and you don't run out of places at the back of your computer to plug bits onto quite as quickly but bear in
mind the cost/benefit equation.
Also look at the software that comes with the scanners you end up choosing between, but don't buy one just
because of the software. A lousy scanner with Adobe Photoshop is still a lousy scanner while a great machine
with an 8-bit graphics package written in basic for DOS v 2.1 all on one 360 KB floppy will still give good
results. Once the drivers are installed your scanner can be accessed out of virtually any modern software
package, including most word processors, and the post-scanning manipulation can be done in any number of
excellent packages available from Adobe, Micrografx, Corel, or a host of others.
Of course once you've bought your scanner you have to install it, set up the software and calibrate your
system but that's another story.
I can't give much more advice than that, but if any manufacturer out there feels like sending me a free,
top-of-the-line scanner I'd be happy to review it.
Reprinted from the April 1998 issue of PC Update, the
magazine of Melbourne PC User Group, Australia
