Calculate dpi value

Christoph Pleger Christoph.Pleger at
Fri Feb 2 03:05:19 PST 2007

On Fri, 2 Feb 2007 11:05:08 +0100 (CET)
"Nicolas Mailhot" <nicolas.mailhot at> wrote:

> Le Ven 2 février 2007 08:48, Christoph Pleger a écrit :
> > Hello,
> >
> > how does the Xorg server calculate the DPI values? What is done if
> > the screen size can be read from DDC and what is done if not?
> If the screen size can not be read and no one specified it in
> xorg.conf using DisplaySize directive generi 17" will be assumed IIRC

Hm, I just added DisplaySize values to xorg.conf on a machine where
because of kernel restrictions the monitor cannot be DDC-probed, but I
cannot see a difference after restarting the X server.

Is it possible that assuming a 17" monitor generally gives a quite good
image on all monitors? And how can the DPI-value be calculated from the
values given for DisplaySize?


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