[argyllcms] Nvidia Quadro RAMDAC problems

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  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 5 Mar 2008 02:09:51 +0100

I use Argyll 0.70 Beta 8 and I would like to share my experience to save 
some "problem finding" time to all the Nvidia Quadro owners and Argyll 

It looks like dispread has currently problems dealing with the 10 bit RAMDAC 
found on Nvidia Quadro chips, here is what I get:

root@mypc ~ $ dispread -v -yl -k mydisplay.cal mydisplay
Number of patches = 836
Setting up the instrument
Can't currently use a RAMDAC which doesn't have 256 entriesCan't currently 
read a RAMDAC which doesn't have 256 entriesPlace instrument on test window.

Being an Argyll newbie and knowing few about color calibration and proofing, I 
ended up having a very wrong ICC profile, because dispread worked on an 
uncalibrated display and, once created the profile, I loaded it at system 
startup using dispwin!
NB: dispwin fails to load mydisplay.cal exactly as dispread, but has strangely 
no problems in loading mydisplay.icc.

The solution (on Linux, on other systems I don't know) is to force an 8 bit 
RAMDAC in the "Device" section of xorg.conf using the following directive:
Option "Dac8Bit" "True"
Restart X server (or simply reboot your system), create your ICC profile, then 
you can safely remove the previous directive.

I suggest the developers should modify dispread code so that it refuses to 
work if such an error appears, moreover currently the error is only visible 
if you use the "-v" flag, otherwise you don't get any warning that something 
very wrong is happening.

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