Problems with monitor calibration and MergedFB/TwinView

Alex Deucher alexdeucher at
Mon Aug 21 20:57:29 PDT 2006

On 8/21/06, Graeme Gill <graeme2 at> wrote:
> Graeme Gill wrote:
> > A number of my users are reporting problems with color management
> > and multiple monitors when running their under NVidia TwinView, or
> > MergedFB.
> OK, since there were zero replies to my query, I guess I
> can conclude that there is zero interest in supporting
> quality color display on X11 systems using NVidia or ATI cards.
> I'll advise my users accordingly.

Despite your unpleasant attitude, I'll reply to this...again.  I
replied to this thread a couple days ago, but if it didn't go through
then here it is one more time...   At the moment it's not currently
possible to adjust the CLUT on the secondary crtc in mergedfb mode.
this is due to the fact that mergedfb is a hack to make multiple
monitors on a multi-crtc card look like a single screen.  The current
driver infrastructure is not really designd to handle multi crtc cards
very well (it's generally assumed one screen, monitor per card). As
such, there's no standard method for accessing the secondary CLUT.
one could add a driver option or an Xv attribute to adjust the gamma
on the second crtc, but those would just be hacks as well.  Hopefully
Keithp's new multi-head aware update to xrandr or the driver attribute
system discussed in the power management thread will provide some
semi-standard method of doing this.  If this is of interest to you
perhaps you could provide a patch or some ideas on implementing a
solution.  The source is available after all.


> Graeme Gill.

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