Ok, I get the right behavior now with cmsSetAdaptationState(0).
Thank you for answering !
Regards,
Vincent
> Date: Mon, 30 Mar 2015 09:51:54 +0000
> From: marti.ma...@littlecms.com
> To: vincent.ponch...@hotmail.fr
> CC: lcms-user@lists.sourceforge.net
> Subject: Re: [Lcms-user] Issue with built in Lab profiles
>
>
>
>
> Hi Vicent,
>
> This is because a requirement of ICC Spec, see:
>
> http://color.org/ICC_white_paper_6_v2_and_v4_display_profile_differences.pdf
>
> You can get the behavior you wish by setting degree of user adaptation
> to 0 at the very beginning of your program:
>
> cmsSetAdaptationState(0);
>
>
> Additionally, you could try transicc command line utility:
>
> > transicc -t3 -d0 -i*srgb -o*Lab
>
> LittleCMS ColorSpace conversion calculator - 4.3 [LittleCMS 2.07
>
> Enter values, 'q' to quit
> R? 255
> G? 255
> B? 255
>
> L*=100.0000 a*=-2.3871 b*=-19.4050
>
> transicc -t3 -d0 -i*srgb -o*XYZ
> LittleCMS ColorSpace conversion calculator - 4.3 [LittleCMS 2.07]
>
> Enter values, 'q' to quit
> R? 255
> G? 255
> B? 255
>
> X=95.0456 Y=100.0000 Z=108.9058
>
> Regards
> Marti
>
>
>
> Quoting Vincent Ponchaut <vincent.ponch...@hotmail.fr>:
>
> > Hi All,
> > I am having an issue with little CMS built in Lab profiles that I
> > have a hard time understanding. When I try to represent the Gamut of
> > my display from its profile by using the API in different Lab spaces
> > created with two different white points (in this case D50 and D65),
> > I would expect to observe some differences.For instance, The White
> > point (1.0, 1.0, 1.0) could not be converted to Lab (100, 0.0, 0.0)
> > in both spaces, as the reference illuminants used for the
> > conversions are different.
> > I wrote the code sample below to enlighten my confusion:
> >
> > /* hProfile is a display profile read from a validated Icc
> > profile beforehand*/
> > cmsHPROFILE labD50, labD65;
> > labD50 = cmsCreateLab4Profile(cmsD50_xyY());
> > cmsCIExyY white; cmsCIEXYZ white_xyz; white_xyz.X =
> > 0.95047; white_xyz.Y = 1.00000; white_xyz.Z = 1.08883; //D65
> > cmsXYZ2xyY(&white,&white_xyz); labD65 =
> > cmsCreateLab4Profile(&white);
> > cmsHTRANSFORM TD50 = cmsCreateTransform(
> > hProfile, TYPE_RGB_DBL, labD50, TYPE_Lab_DBL,
> > INTENT_ABSOLUTE_COLORIMETRIC, // same with relative 0
> > ); cmsHTRANSFORM TD65 = cmsCreateTransform(
> > hProfile, TYPE_RGB_DBL, labD65, TYPE_Lab_DBL,
> > INTENT_ABSOLUTE_COLORIMETRIC, // same with relative 0
> > );
> > const int SIZE = 64; int Errcount = 0; double sum = 0.0;
> > for (int r = 0; r < SIZE; ++r) for (int g = 0; g <
> > SIZE; ++g) for (int b = 0; b < SIZE; ++b)
> > { cmsCIELab LD50, LD65;
> > double RGB[] = { double(r)/double(SIZE-1),
> > double(g)/double(SIZE-1),
> > double(b)/double(SIZE-1) };
> > cmsDoTransform(TD50,RGB,&LD50,1);
> > cmsDoTransform(TD65,RGB,&LD65,1); sum +=
> > abs(LD50.L - LD65.L) + abs(LD50.a - LD65.a) + abs(LD50.b - LD65.b);
> > if (LD50.L != LD65.L || LD50.a != LD65.a || LD50.b
> > != LD65.b) { Errcount++;
> > } }
> >
> > As a result, absolutely no difference has been observed.
> > Could someone please give some more precision about those built in
> > profiles? Did I misunderstand something?
> > Best regards,
> > Vincent.
>
>
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