Re: Gamma values on Windows XP
Re: Gamma values on Windows XP
- Subject: Re: Gamma values on Windows XP
- From: Chris Murphy <email@hidden>
- Date: Wed, 12 Feb 2003 11:48:04 -0700
On Wednesday, February 12, 2003, at 09:33 AM, "Bruce J. Lindbloom"
<email@hidden> writes:
4) Always load your VLUTs with ramps and keep them there.
5) Profile your monitor (while the VLUTs are already ramped and will
remain
forever ramped) and let Photoshop color manage the display for you.
The only product I'm thinking of at the moment that will do only
display characterization without first calibration is ColorVision
OptiCAL. And I'm not sure if they "reset the VLUT" prior to doing this,
or if it's just prior to a calibration. I pretty sure I've see it
happen just prior to calibration.
The other problem is that some video cards are jacked up. Maybe I've
just had bad luck with a few of them, but the nVIDEA GeForce 2MX card I
have in my PowerMac 867 - when the LUT gets zero'd out just before
calibration - produces a *strong* green cast on pretty much every
monitor I've hooked it up to. And on an old Powerbook the same displays
would have a semi-strong magenta cast.
So the in/out voltage of each channel from the video card must not be
exactly the same, when the VLUT is set with the same ramps. Thus - some
calibration is needed in order to gray balance the monitor to something
reasonable. If it's all done in the CMS, only a window that's being
color managed will be gray balanced. A gray desktop pattern won't be
gray. In theory everything should eventually pass through the CMS on OS
X, but that's not currently the way it is. So in the meantime, I think
we're going to need at least some minimum calibration capability. But
we also need to hold the video card vendors to a higher standard too.
6) Down with 'vcgt'! <g> (Except when using it to force ramps into the
VLUTs.)
*If* it's given that we need some kind of calibration, vcgt I think is
a good thing because we don't need those silly startup applets to apply
calibration. The Display Manager handles it. And if you select a
different profile (let's say you're going to do some video editing and
want to compensate for a lower light level that will be used to few the
video), the LUT is updated automatically by the Display Manager. At
least, on Mac OS. On Windows, vcgt is ignored. So not only do you need
a silly startup applet, but if you select some other profile and make
it active, the LUT isn't update to what it should be for the profile to
be valid.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
---------------------------------------------------------
Co-author "Real World Color Management"
Published by PeachPit Press (ISBN 0201773406)
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