Hi Gerhard, Well, this is the old question again. I have even submitted a paper to ICC regarding that issue.
Anyway, some answers. This particular profile is a "mix" between v4 and v2. If you list the tags, you will find there is a chromatic adaptation tag present. Well, lcms at its 1.14 incarnation implements absolute intent as "no adaptation", so, it uses the chromatic adaptation tag to "undo" the chromatic adaptation and therefore, recover the true primaries. Next version will have a way to control if absolute intent should behave as observer is fully adapted (this is called the ICC-absolute intent) or as observer not adapted at all (very useful in a match to screen environments). See some details of that here: http://www.color.org/ICC_white_paper_6_v2_and_v4_display_profile_diffrerences.pdf The CVS has this feature already implemented. The new function is "cmsSetAdaptationState" Argyll probably doesn't handle chromatic adaptation tag, and then, since white point is D50, you are getting same values as rel. colorimetric. That will be the behavior of lcms with adaptation state=1 (totally adapted). The default behavior is adaptation state=0 (not adapted) I think the different values are because slight differences between D65 in the stardard sRGB profile and in the black body locus on 6504K, as well as the lam-rigg matrix (cone primaries). I will take a look on that. All makes sense if you take into account chromatic adaptation applies only for *illuminant* and not for *media*. That is, a paper under a D65 illuminant should be profiled doing chromatic adaptation from D65 to D50, not using media chromaticity. See my paper here: http://www.littlecms.com/Absolute%20colorimetric%20intent1.pdf Regards, -- Marti Maria The littlecms project. www.littlecms.com ----- Original Message ----- From: "Gerhard Fuernkranz" <[EMAIL PROTECTED]> To: "Marti" <[EMAIL PROTECTED]> Cc: "LCMS mailing list" <lcms-user@lists.sourceforge.net>; "Graeme" <[EMAIL PROTECTED]> Sent: Saturday, July 16, 2005 7:45 PM Subject: Re: [Lcms-user] XYZ values of colorants seem different? Marti schrieb: >Just create a transform RGB profile -> XYZ using abs. >colorimetric, then feed (255, 0, 0), (0, 255, 0) and (0, 0, 255) > >For example: > >F:\lcms>icctrans -t3 -i "sRGB Color Space Profile.icm" -o*XYZ >little cms ColorSpace conversion calculator - v1.9 >Enter values, 'q' to quit >R (0..255)? 255 >G (0..255)? 0 >B (0..255)? 0 > >X=41.2415 Y=21.2616 Z=1.9318 > Hi Marti, you just triggered me to bring up an issue I already wanted to discuss. Obviously, the results depend on the sRGB profile being used. With the old sRGB profile from 1998, one gets the result you mentioned above. However, with the new sRGB profiles from July 2004, which can be downloaded from the ICC web site www.color.org, the result is different: $ icctrans -t3 -i sRGB_IEC61966-2-1_noBPC.icc -o \*XYZ little cms ColorSpace conversion calculator - v1.8 Enter values, 'q' to quit R (0..255)? 255 G (0..255)? 0 B (0..255)? 0 X=43.0878 Y=22.3145 Z=2.5116 And with Argyll CMS, the new sRGB profile gives me the same results for relative colorimetric and for ICC-absolute intent: $ icclu -ia sRGB_IEC61966-2-1_noBPC.icc 1 0 0 1.000000 0.000000 0.000000 [RGB] -> MatrixFwd -> 0.442668 0.232205 0.024054 [XYZ] $ icclu -ir sRGB_IEC61966-2-1_noBPC.icc 1 0 0 1.000000 0.000000 0.000000 [RGB] -> MatrixFwd -> 0.442667 0.232205 0.024053 [XYZ] According to the header, the new sRGB profile is a V 2.0.0 profile, however, its media white point tag records D50 (not D65, but D65 adapted to D50), and the profile also does contain a "chad" tag. In the past, my understanding of ICC-absolute intent was the unchanged reproducion of the source XYZ color on the destination device (without performing any CAT), only the luminance may possibly differ. In the mean time, I'm no longer sure. There seems to exist a seconds interpretation as well, which interprets ICC-absolute intent as an *illuminant relative* transformation (i.e. CAT from source illuminant to destination illuminant), with the consequence, that relative colorimetric and iCC-absolute intent give the same result, if source and destination profiles are monitor profiles, since media WP equal to illuminant is assumed for monitor profiles. Basiaclly all three transformations make sense 1. Media relative, i.e. source media WP is mapped to dst media WP (-> "relative colorimetric") 2. CAT from source illuminant to destination illuminant, discounting only the illuminant, but not the paper color 3. Source XYZ colors map unchanged to dst XYZ colors, (i.e. sRGB image is reproduced very blue-ish on a D50 monitor) but there are only two colorimetric intents defined (relative colorimetric and ICC-absolute), thus only either (2) or (3), but not both, can be the "correct" interpretation of ICC-absolute intent. So I'm a bit confused, and I'm wondering, what's now really the correct interpretation of ICC-aboslute intent? Thanks, Gerhard -- No virus found in this incoming message. Checked by AVG Anti-Virus. Version: 7.0.323 / Virus Database: 267.8.16/50 - Release Date: 15/07/2005 -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.323 / Virus Database: 267.8.16/50 - Release Date: 15/07/2005 ------------------------------------------------------- SF.Net email is sponsored by: Discover Easy Linux Migration Strategies from IBM. Find simple to follow Roadmaps, straightforward articles, informative Webcasts and more! 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