Markk wrote:
> I am a very new user to POVRAY.
> 
> I have rendered and saved my image as an uncompressed Targa file. The image
> looks great, but it is only 72 ppi. Is there a way to set the ppi during
> rendering in POVRAY?

Okay, this has already been answered quite thoroughly, particularly in 
Thorsten's reply, but I'm going to add my own two cents anyway, and 
maybe give it a little different slant.

Essentially, the ppi value (or more commonly called dpi--same thing...) 
is fairly irrelevant.  It is nothing more than a data value in the file 
header and is completely independent from the actual image data itself. 
  (That is, in the graphic formats that support it, which, according to 
Christoph, Targa does not.)  And it has been pointed out, this value can 
be changed with a graphics editor.  But I want to emphasize, this 
changes that one data value and does nothing to the actual image.

Now, when an image is displayed on a computer screen, this ppi/dpi value 
is totally ignored because the screen has a fixed pixel size.  The 72 
ppi value is usually used as a "generic" average value for computer 
screens.  Obviously, in reality it varies, nevertheless this value is 
used as an average.  And this is why 72 dpi is often used by graphics 
software as a default value.

However, things change a bit when we come to print the image.  Now the 
ppi/dpi value _can_ be used -- it might or it might not, depending on 
the printing software and the printer's capabilities.  If it _is_ used 
the print will be this specified "natural" size.  But even here, the 
printing software will usually have a "print preview" or other means of 
adjusting the size (and position) of the printed image, which also makes 
the stored ppi/dpi value unimportant.

Now, to your second question...

 >                How do people generete publication quality images with
 > POVRAY???

That's due to the _size_ of the image (in pixel dimensions).  More 
pixels--higher quality, fewer pixels--lower quality.  It's that simple.

The upshot of all this is -- forget about the ppi value.  For most 
practical purposes this value is totally irrelevant.

      -=- Larry -=-

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