Re: graphicsmagick won't "gm identify" resolution correctly

On Thu, 5 Aug 2004, Benjamin Adler wrote:

> I have some tif-files on which "gm identify [-verbose]" shows a resolution of
> 0, 0 pixels/inch. Quite possibly that is only with files that have been
> created with a certain version of Kodak's DCS PhotoDesk. Photoshop shows a
> resolution of 72dpi on those images.
>
> The example.tif can be downloaded at
> http://politbuero.dyndns.org/example.tif.bz2. Sorry, the file is 11mb in
> size, I had no smaller file showing this problem, and when I open and save it
> it photoshop, the problem is gone. Can an image have a resolution of 0 dpi?
> Is there any way to fix this, other than opening and saving all those files
> in photoshop?

A returned resolution of 0 dpi indicates that the image file does not 
contain a resolution setting.  Many/most image file formats do not 
support a resolution setting.  For others, it is optional.

Photoshop is likely "fixing" the resolution by updating the image with 
a default resolution value.

You can fix the resolution setting for images that lack an existing 
setting by executing

   gm mogrify -density 150x150 example.tif

Unfortunately, in order to not overwrite an existing resolution, you 
would need to use something like

   gm identify -format "%xx%y" example.tif

to query the existing resolution and only update it if the result is 
"0x0" (or some other value which is unacceptable to you).

Bob
======================================
Bob Friesenhahn
[email protected]
http://www.simplesystems.org/users/bfriesen


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