On Tue, Apr 07, 2009 at 03:37:57PM +0100, norman wrote:
> > As for your original question.
> > if you have 4800x9600 ppi, and you scan an inch square of material,
> > you will end up with 4800x9600 pixels.  Thus the question if you are
> > having a laugh, as your question seemed trivial.
> I am really sorry you see my questions as trivial, they are not meant to
> be. Much of my difficulty is one of understanding the terminology used.

Not a problem at all.  Professionals get this kind of stuff wrong all
the time.

Yes, if you were to scan a 5 inch square image at 4800x9600 ppi, then
you should get 24,000 x 48,000 pixels.  So, something else is going
on.  Your hardware is only capable of 600dpi (I just looked it up on
Canon's website), it can double sample in one direction to get close
to 600x1200, then interpolate to get up to the ranges of 2400.  So, it
really doesn't make sense to scan any higher than your base of 600dpi.
But that doesn't address the other problem you mentioned.  729 pixels
/ 5 inches is 149dpi, which is off by a factor of 4 from what the
hardware is supposedly capable of and 16 from what you think you
scanned at.  I would make sure that the GIMP isn't loading some
embedded thumbnail instead of the real image.  If you are in windows,
you should be able to right click on the image and go to properties.
The size that Windows thinks the image is is usually stored in the
"Summary" tab.  If you are on a Mac, I would suggest using Preview,
then there should be a view image info menu button somewhere (not near
a mac at the moment).  If you are on Linux, then you should be able to
type "file imagename.ext" and get the file size.

> 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 didn't think that for one second.  I assumed that unit conversion
wasn't understood rather than that you were seeing something contrary
to what the math tells you.  I apologize.


"The man who does not read good books has no advantage over 
 the man who cannot read them."
 -- Mark Twain

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