[argyllcms] Re: Nvidia Quadro RAMDAC problems

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 06 Mar 2008 00:37:51 +1100

lists@xxxxxxxxxxxx wrote:
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.

Hmm. I wasn't aware than any currently available cards had 10 bit frame buffers!

Any idea what the videoLUT output resolution is ?

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.

I'll try and go one better by fixing it so that it should work with a 10
bit frame buffer and 1024 VideoLUT entries. Hard for me to test though ...

Graeme Gill.

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