[Lcms-user] Re: [Lcms-user][OpenICC] vgct tags

[Hal V. Engel]

On Monday 17 October 2005 11:18 pm, Greg Sullivan wrote:
> I too would like LCMS to support monitor calibration. (although I don't
> care how and where it stores the calibration data - just as long as there
> is a means to load the data into the graphics card)
>
> Having said this I understand the reasons why it doesn't, and may never
> support calibration. But it'd be nice. :) :)
>
> Greg.

The use of vcgt tags in monitor profiles is a mixed bag.  If your 
hardware/driver setup allow for it's use (on most hardware one monitor per 
video card) then there are advantages (and dangers) to having and using it.  
But on most setups with more than one monitor per video card having vcgt tags 
is something that simply does not work and in most cases these profiles can 
not be correctly used on this type of setup.

My plan for LPROF is to support the creation of monitor profiles with or 
without vcgt data as a user option.  That way the user can control how to 
generate the profiles based on their systems requirements.  

Since monitor profiling is an area where LPROF will be under going significant 
change over the next few months I am very open to feedback from those on this 
list concerning it's features and in the context of this thread specifically 
what things should be included to support proper hardware calibration.

Please feel free to go to the feature request tracker for the LPROF project 
and add any features that you think should be included.  Also perhaps it 
would be good to work through some of these issues here to see how this fits 
into the other work that is happening to make these things work together.

Hal


>
> -----Original Message-----
> From: lcms-user-admin at lists.sourceforge.net
> [mailto:lcms-user-admin at lists.sourceforge.net] On Behalf Of Stefan Döhla
> Sent: Tuesday, 18 October 2005 03:51
> To: Lcms Liste
> Subject: Re: [Lcms-user] Re: [Lcms-user][OpenICC] vgct tags
>
> >> I have to add a very important item: The profiles, created with
> >> ProfileMaker, basicccolor display, Monaco, ... do include the vcgt and
> >> are not containing valid device characterization if the vcgt is not
> >> taken into account. This does mean, that an ICC-lib should support
> >
> > This is an OS issue. Independent of an CMM.
> >
> >> vcgt tags, as they are required to correctly apply the data of
> >> these profiles (which are most likely the majority).
> >
> > Again an OS issue. The profile attached to an screenshot image is
> > completely valid in the sense of the ICC spec. Why would someone need the
> > linearisation data of an printer, With the Cmyk ICC profile a separated
> > image is completely described, as it can be converted to pcs.
>
> What I wanted to say is simply: You should not ignore these tags
> completely, since they are accidentaly very powerful. E.g. changing
> the whitepoint with a vcgt tag is fairly easy, so don't apply it and
> all data contained in the profile is invalid.
>
> You are right in terms: it's the responsibility of the OS to apply
> these changes. But there's no better/cleaner way for now to say that
> certain calibration data lead to a certain profile (at least it's the
> impression when looking at all the commercial profilers).
>
> Stefan