Hello Vicent,
This is now fixed in GIT. Thanks for reporting
Best regards
Marti
Vincent Ponchaut <vincent.ponch...@hotmail.fr> escribió:
>> > Hi everyone,
>> > I am trying to find a generic approach for reading the 'lumi' tag
>> > accurately, using Little CMS 2.7. I use ICC profiles that are
>> > generated with XRite i1 display pro, and it seems that the X & Z
>> > values of the CIEXYZ 'lumi' value are not 0 (making the profile
>> > wrong according to the ICC spec).
>> > I am under the impression that little CMS applies a kind of
>> > correction whenever this kind of 'lumi' tag is detected (diving X,
>> > Y, and Z by 100.0 ? ).
>>
>>
>> Hello Vicent,
>>
>> LittleCMS does nothing with the contents of luminance tag. It just
>> returns the XYZ contained it it. Make sure to use the right type, which
>> is cmsCIEXYZ. Otherwise yes, you can mix read raw with read cooked, but
>> what you say closing and reopening the handle gives you different
>> values is very suspicious. Could you show us the portion of code that
>> reads that tag? Thanks. Oh, also make sure to try the latest code from
>> GIT, there are some fixes that may be relevant.
>>
>> Regards
>> Marti
>>
>
> Hi Marti,
> The "correction" that I mentioned would be the NormalizeXYZ function
> that is used in _cmsReadXYZNumber:
> [...]
> XYZ->X = _cms15Fixed16toDouble(_cmsAdjustEndianess32(xyz.X));
> XYZ->Y = _cms15Fixed16toDouble(_cmsAdjustEndianess32(xyz.Y));
> XYZ->Z = _cms15Fixed16toDouble(_cmsAdjustEndianess32(xyz.Z));
>
>
> NormalizeXYZ(XYZ);
> [...]
>
> I think that this may be the reason why the luminance of my profile
> is not read correctly.
> So I tried to bypass this and observed the behavior I described.
> Sample code:
> /* Open profile handle */ cmsHPROFILE hProfile =
> cmsOpenProfileFromFile("testProfile.icc", "r");
> /* Read luminance in a "classic" way */ cmsCIEXYZ *lumi =
> (cmsCIEXYZ*)cmsReadTag(hProfile, cmsSigLuminanceTag);
> cout << lumi->X << lumi->Y << lumi->Z << endl;
> /* Read luminance from raw data */ cmsS15Fixed16Number
> buffer_s15f16[20]; cmsReadRawTag(hProfile, cmsSigLuminanceTag,
> buffer_s15f16, 20);
> lumi->X =
> cms15Fixed16toDouble(cmsAdjustEndianess32(buffer_s15f16[2]));
> lumi->Y =
> cms15Fixed16toDouble(cmsAdjustEndianess32(buffer_s15f16[3]));
> lumi->Z =
> cms15Fixed16toDouble(cmsAdjustEndianess32(buffer_s15f16[4]));
> cout << lumi->X << lumi->Y << lumi->Z << endl;
> This produces the following output: 0.527483 0.571429 0.697399
> 0.527481 0.571426 0.697403
>
> However, that is not the case with the following code (that is
> practically the same except for closing/reopening the profile
> between the two calls):
> /* Open profile handle */ cmsHPROFILE hProfile =
> cmsOpenProfileFromFile("testProfile.icc", "r");
> /* Read luminance in a "classic" way */ cmsCIEXYZ *lumi =
> (cmsCIEXYZ*)cmsReadTag(hProfile, cmsSigLuminanceTag);
> cout << lumi->X << lumi->Y << lumi->Z << endl;
> /* Close then reopen */ cmsCloseProfile(hProfile);
> hProfile = cmsOpenProfileFromFile("testProfile.icc", "r");
> /* Read luminance from raw data */ cmsS15Fixed16Number
> buffer_s15f16[20]; cmsReadRawTag(hProfile, cmsSigLuminanceTag,
> buffer_s15f16, 20);
> lumi->X =
> cms15Fixed16toDouble(cmsAdjustEndianess32(buffer_s15f16[2]));
> lumi->Y =
> cms15Fixed16toDouble(cmsAdjustEndianess32(buffer_s15f16[3]));
> lumi->Z =
> cms15Fixed16toDouble(cmsAdjustEndianess32(buffer_s15f16[4]));
> cout << lumi->X << lumi->Y << lumi->Z << endl;
> This version produces this output:0.527483 0.571429 0.697399
> 527.483 571.429 697.399
>
>
> I can make my code work fine by using only the version that reads
> the tag from raw data, but I could not, for example, make an
> algorithm that goes: 1) Open profile 2) Read Luminance in a
> "classic" way3) Sanity check of the obtained values4) If the value
> is not correct, read luminance from raw data
> Without having a close/reopen step in between.
> I will definitely give a try to the code on GIT, thanks !
> Best regards,
> Vincent
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