Re: [Lcms-user] ICC profiles -> primaries

[Kai-Uwe B. <ku...@gm...>]

Marti,

thanks for the hint.

An other question comes to my mind:
for the absolute intent you need to guess, when chrm or chad are absent?

Or how does you find out the original primaries, which are lost during the 
Wtpt->D50 transformation?


regards
Kai-Uwe Behrmann
                                + development for color management 
                                + imaging / panoramas
                                + email: ku...@gm...
                                + http://www.behrmann.name



Am 10.10.05, 18:54 +0200 schrieb Marti:

> 
> Kai-Uwe,
> 
> Just take the ICC profile as a black-box. The fact some profiles
> are implemented as matrix-shaper should be irrelevant.
> 
> If you understand primaries as the chromaticity of colorants,
> obtaining the primaries should be as easy as using an absolute colorimetric
> transform from the given profile to XYZ space, and then obtaining the XYZ
> value of each colorant.  This will work on all colorspaces,
> not only on RGB.
> 
> Regards,
> --
> Marti Maria
> The littlecms project.
> www.littlecms.com
> 
> 
> 
> 
> 
> ----- Original Message ----- From: "Kai-Uwe Behrmann" <ku...@gm...>
> To: "Lcms Liste" <lcm...@li...>
> Sent: Thursday, October 06, 2005 8:01 PM
> Subject: Re: [Lcms-user] ICC profiles -> primaries
> 
> 
> > Hi,
> > 
> > even in danger to repeat this toppic, here comes my own take:
> > 
> > The primaries stored in the rXYZ,gXYZ and bXYZ tags are part of the
> > RGB<->XYZ conversion matrix. They are related to D50. The whitepoint in
> > wtpt represents the original whitepoint of the media. 
> > To convert from D50 primaries to oroginal wtpt primaries the chad tag was
> > introduced. It holdes the conversion matrix to come from D50 primaries to
> > wtpt primaries.
> > 
> > Additional the chromaticity (chrm) tag, natively being in wtpt, can be
> > used to hold the origin in the profile.
> > 
> > Without knowing the chromaticities (chrm) or the transform (chad)
> > conversion is guessing of the right transform. Bradford is a good
> > candidate.
> > 
> > The good news, now I understand it, the chrm tag is included by lcms
> > during RGB matrix profile generation. Thanks!
> > 
> > regards
> > Kai-Uwe Behrmann
> > + development for color management +
> > imaging / panoramas
> > + email: ku...@gm...
> > + http://www.behrmann.name
> > 
> > 
> > Am 03.10.05, 12:38 +0200 schrieb Kai-Uwe Behrmann:
> > 
> > > Hi,
> > > 
> > > is there a example to get the real xy primaries from an given matrix
> > > profile, including white point adaption?
> > > 
> > > regards
> > > Kai-Uwe Behrmann
> > > + development for color management +
> > > imaging / panoramas
> > > + email: ku...@gm...
> > > + http://www.behrmann.name
> > > 
> >