[Openicc] Re:vgct tags

[Chris Murphy]

On Oct 15, 2005, at 2:00 AM, Kai-Uwe Behrmann wrote:

> As I understand, Microsoft will differ to osX in the way to set up
> things, as well as Linux will. The ICC did not try to cover such
> differences under one cover. If we find a way to include Linux OS
> specifics into the profile I would like to support it.

I don't have a problem with the differences or lack of universal  
support for vcgt per se, just because these profiles aren't meant to  
be portable. It's not like a printer where its behavior is the same  
regardless of what machine it's moved to (so long as the drivers for  
the printer cause the same behavior to occur); a display only works a  
particular way depending on the video card it's attached to, so the  
LUT information doesn't have to be in the profile. It just has to be  
on that machine somewhere.

What I don't like on Windows is the potential for conflict. On  
Windows, each display calibration product installs two applications.  
The main application and a small startup applet whose sole purpose is  
to find some preference file, read the LUT data from it, and apply it  
to the video card. When you upgrade your calibration software, the  
old one isn't automatically removed, which means you can have two  
such startup applets on the machine running in conflict with each other.

On Mac OS, Apple took control of the situation by coming up with vcgt  
and the display manager grabs the information from the currently  
selected display profile and updates video card LUTs accordingly.

The trend in the future however is probably not video card LUT, but  
display side LUT. So that too will take proprietary software, not OS  
hardware agnostic software like Apple's display manager, because  
there is no standard way to communicate to displays. So either  
someone compels the display manufacturers to do this in a standard  
way, or every developer will have to include display specific code to  
do display LUT updating (which is currently the case and why it's a  
problematic area).

The nice thing is that display side calibration totally bypasses the  
video card mess on Windows, whereas on Mac OS there are standard ways  
to communicate with video cards, unlike Windows and likely Linux/BSD  
as well.

I think if this video card and display LUT to remain proprietary is a  
driver requirement to translate some OS specific settings language  
into whatever proprietary signals are need to achieve a result. Thus  
the "standard" as it were, it OS specific, rather than at the whim of  
the display companies. Unless you get Microsoft to tie that kind of  
functionality to their Windows logo usage, I don't think display  
companies will budge an inch.



Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
-------------------------------------------------------------
Co-author "Real World Color Management, 2nd Edition"
Published by PeachPit Press (ISBN 0-321-26722-2)