[EMAIL PROTECTED] (2004-11-29 at 1021.34 -0500):
> I have a large photograph that I cropped and then reduced in size. But when I 
> do that the pixels per inch goes up. How do I reduce an image in size yet 
> keep the pixels per inch at e.g., 90? I scanned at 50 PPI (the lowest Xsane 
> will do.) But when I reduce it to roughly half size by resizing the image 
> image->scale image 
> the PPI shoots up to 164. If I reset the resolution to 90 then the dimensions 
> go up. 

I started with a 10*10 inch image and 90 DPI (so it will use 900
pixels in each dimension). It is "big" and 90 DPI, and want it to be
half size, 5 inches but still 90 DPI.

Then in that dialog:

1. Set the units in the top most drop down menu to in(ches), so two
   top most labels will show 10.000", and the two entry boxes below it
   will show 10.000. This step is optional, but shows how things

2. Input 0.5 in the Ratio X, and as the link button is on, Y will
   change to 0.5000 as soon as you hit Tab. New Width and Height above
   it will change to 5.000 automatically. The boxes in Print Size &
   Display Unit frame will too. But Resolution boxes stay at 90.

3. Accept that settings and wait for Gimp to do the maths.

Finally check in View/Image Info that each axis is 5 inches at 90 DPI,
and logically using 450 for that.

Playing with Print Size and Display Units makes one go up when you
lower the other, and viceversa, they are interrelated and they are
merely the way to access the fields some file formats have to record
suggestions for printing. To really modify the pixel data, you have to
use the top frame controls, Pixel Dimensions.

Instead of Ratio, you can also use New Width and Height in Pixel
Dimensions ones. You _have_ to do step 1 so Gimp know you are going to
input inches, and then you can type 5 in one of the top boxes, Ratio
will be the ones that change to 0.500.

As it has been said already, all this interrelations can sound
complex, but are useful *, provided you know "what will move when you
pull from a thread". This could get a video, or some graphical
representation of the relations at least:

        Top frame sizes <----> Top frame ratios

     Bottom frame sizes <----> Bottom frame resolutions

              Top frame  ----> Bottom frame sizes

Bottom frame size boxes  ----> Top frame sizes if set to physical units

* Image from a 3D app or a screen capture or whatever, the point is
that nothing matches, it says 1000 pixels, 72DPI and 13.889 inches,
but you need 2 inches and 300 DPI. So you set 300 in DPI box (PS&DU's
W and H will say 3.333), then change top drop down menu to inches and
type 2 in PD's Width (PS&DU's W and H will go to 2, and PD's Scale
will go to 0.600).

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