> I need to create a picture with a specific size and resolution.
> I am Linux user so I have a .ini file which contains info like the picture
> size in pixels, e.g. :
> Width=4000
> Height=3200
> But, I don't how to set the resolution. I've actually been asked to create a
> picture with 300 DPI with a size of 213 x 161 mm
> How do I do that ?

DPI is "irrelevant", what you want to know about from a printing/quality 
point of view is the number of pixels. DPI only comes into the game when
you consider printing an image at a paricular size. For example, your 4000
pixel wide image above, if printed 10 inchs wide will be 400DPI. The exact
same image printed at 20 inchs will be 200DPI.....a clear example of why
DPI as a measure isn't so useful.

The problem is that the printing industry is so steeped in the use of DPI
that they often don't understand what's really going on. So when they give
you a DPI value and an image size you simply multiply them to give the
right number of pixels. So for your example 300DPI at 213mm is
   300 * 213 / 25.4 pixels
or about 2500 pixels. 

Now most image formats do have a DPI setting as part of the file information,
but again it is largely irrelevant except at the point of actually representing
the image on some media. It is the number of pixels that determines the 
(potential) resolution and information content.

-- 
Paul Bourke
pdb(NOSPAM)swin.edu.au

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