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

[Marti <ma...@li...>]

Hi Kai-Uwe.

chad applies only to illuminant, so it depends on which kind of
profile. On printer profiles, no chromatic adaptation is assumed.
On Display profiles, lcms uses a sort of linear Bradford (same as
sRGB). Works well on most workspace profiles.

Regards,
--
Marti Maria
The littlecms project.
www.littlecms.com

----- Original Message ----- 
From: "Kai-Uwe Behrmann" <ku...@gm...>
To: "Marti" <ma...@li...>
Cc: "Lcms Liste" <lcm...@li...>
Sent: Tuesday, October 11, 2005 6:37 PM
Subject: Re: [Lcms-user] ICC profiles -> primaries


> 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
>> > > 
>> > 
> 
> 
> 
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