On Tue, 2009-04-07 at 15:37 +0100, norman wrote:
> I scan a photograph
> which is, say, 5 inches square and then display that scan on my monitor,
> it will measure 24,000 pixels X 48,000 pixels. To test this on my rather
> cheap Canon LIDE20 I scanned a picture which is 5 inches square saved
> the file, opened the file in GIMP, cropped so that only the picture was
> there and GIMP said it was 729 pixels X 729 pixels.

729/5 = ~145 ppi.  Assuming you're reading the size of the image
correctly in GIMP, it appears your scan wasn't at that much higher
resolution.  Note that scanners convert reflected light (analog signals)
into pixels (digital signals) and can do this by varying the range of
sampling of the light.  Sometimes the higher resolution they advertise
is actually a function of their software and not of their hardware.
Their hardware may not be able to sample at those higher rates.  In that
case, and if you aren't using their software, you probably won't get the
higher ppi resolution.

If you are using their software to scan (I haven't read this whole
thread but in this case it would mean you're using Windows) then try
opening the image in another program and see if it will tell you the
pixel size of the image.  If you get two programs telling you that the
image is 729x729 pixels, then your scanner/scanning software isn't doing
what it says its doing.

> Please explain and, just in case you think I am some youngster trying to
> get his homework done, I was 81 years old last birthday.

I hope I'm still learning new things when I'm 81 (I'm on the high side
of the 40's).  :-)

Michael J. Hammel                                    Principal Software Engineer
mjham...@graphics-muse.org                           http://graphics-muse.org
The essence of our practice is to involve others in a world for which even
we do not understand the rules.  --  Michael J. Hammel, on writing

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