I hope I have not misconstrued your question / wording.

You used the word "scan" in conjunction with your camera.  Your camera
is not a scanner.  It has a very different dpi/ppi than a scanner.

Scanners use A x B dots/pixels maximum per square inch.  However, what
you get from your scanner (up to that maximum) is what you tell it to
give you, for example 600 x 600 dots/pixels per square inch.

On scanners, most humans have little use for their so-called maximum
resolution.  However, one practical application for using higher
resolution settings is if you want to scan a small object, such as a
postage stamp, and blow it up to a wall-sized poster.  Scanners scan at
100% of actual object size, so a 1x1-inch object at 600 x 600 is going
to show up in your image software as 600 x 600 pixels/dots.  The
resolution of your computer monitor and the zoom/magnification (for
viewing purposes only) setting in your image program will affect how
large it appears on your computer screen.  However, if you PRINT that
image on a 600 dpi/lpi/ppi PRINTER, then it will come out 1x1-inch on
the paper (unless you make it larger, i.e. more pixels/dots, in your
image program).

(I find it nearly impossible to explain to folks the difference between
viewing and printing in regard to resolution.  It takes a while to "get

So, to scan that postage stamp that you want to turn into a wall poster,
you might scan it at a very high 2400 x 2400 resolution.  Then, in your
image program, change the size from 1x1-inch up to 20x20 inches AT THE
VERY  SAME TIME AS YOU _reduce_ the resolution to 300x300 dots/pixels
per inch.  My understanding is that you have to do it at the same time
for best results. You thus are SPREADING the 2400 x 2400 pixels over an
area of 6000 x 6000 pixels (20 x 300).  The result won't be crisp and
clear when printed, but then it is a wall poster meant to be viewed from
some distance.  Good luck finding a printer that can print it (a
36,000,000 pixel/dot, 20x20 inch image).  ;-)

Cameras use a different C x D maximum dots/pixels per square inch than
scanners.  You might have to find the info buried in the manual.
Scanners and cameras are two completely different animals in several
ways.  But more to the point, it is my understanding that they use a
maximum total image/data size for the picture.  However, again, what you
actually get is what you tell it to give you, up to that maximum.  You
probably got 729 x 729 (i.e. 531,441 dots/pixels or "half megabyte")
because you told it to use a particular size/quality.  I don't have a
lot of experience with cameras seem to use words to describe the image
"size" or "quality", or "speed", such as "good", "better", "best".  If
"good" is 729 x 729 and you use the setting of "good", then whatever is
in the picture is 729 x 729.  If that is not enough detail, then the
picture must be taken zoomed in so that whatever it is you want in the
picture is taking up more of the image area.

I suggest if you have further questions about this, you find a mailing
list or forum about cameras, scanners, and computer graphics, etc.  The
Gimp list is meant to be most about GIMP.

BTW, You got a LOT more action on this than I get when I ask a GIMP
question.  Nobody seems to want to answer my GIMP questions.  :-(


On 04/07/2009 10:48 AM, Michaela Baulderstone wrote:
> I'm 36 with a post grad degree & I can't figure out how to get an image to
> specific size
> Cheers
> M
> -----Original Message-----
> From:
> [] On Behalf Of norman
> Sent: Wednesday, 8 April 2009 12:08 AM
> To: gimp-user@lists.XCF.Berkeley.EDU
> Subject: Re: [Gimp-user] pixels to dpi
> < snip >
>> 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.
> For example and, assuming I understand correctly, if 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.
> 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.
> Norman
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