Thank you for the reply. I figured out on Friday, that I used the Null
and custom profiles in wrong order (found an old example for lcms 1 and
adapted it). But almost all Lab values were giving me out of gamut
warning. So I implemented my own warning, that I make Lab -> ICC -> RGB
transform and the reverse one. Then I compute deltaE of the original Lab
and the one after conversion to RGB and back. I set a threshold of
deltaE 5 (found this in lcms constants and sounds reasonable) and this
gives me much better results. Is this a good way or should I trust the
proofing transform more? Thank you.
Regards,
Martin
On 24. 11. 2013 11:04, marti.ma...@littlecms.com wrote:
>
>
> Hello Martin,
>
> You almost got it. It doesn't work because the order is wrong.
>
> Ok, lets revise what you want to do. You said, you want to check if a
> Lab color is withing an ICC profile gamut. That's fine, and this
> functionality can be obtained by cmsCreateProofingTransform. Ok so far.
>
> Then the question is how you want to mark this. One possible solution
> would be to use an array of byes. If the color is withing, then the
> byte would be set to '00'. If out of gamut 'FF'.
>
> To do that, we could use the NULL profile. This is an special 1-channel
> profile that always returns 0. Being 1-channel, this can be interpreted
> as gray.
>
> The trick comes now with the alarm color. NULL profile will return always
> 0, but the alarm color will bypass the transform and therefore give
> whatever value you set. 'FF' for example.
>
> So that's how the transform works. There are some leaks here since the
> profiles are created and never set free, but you can take the idea.
>
> There is no softproofing here, only gamut check. And then you could
> do the check by calling cmsDoTransforms in this way;
>
> cmsHTRANSFORM xfrm =
> cmsCreateProofingTransform(cmsCreateLab4Profile(NULL), TYPE_Lab_DBL,
> cmsCreateNULLProfile(), TYPE_GRAY_8, cmsCreate_sRGBProfile(),
> INTENT_RELATIVE_COLORIMETRIC, INTENT_ABSOLUTE_COLORIMETRIC,
> cmsFLAGS_GAMUTCHECK);
>
> cmsCIELab Lab = { 50, -125, 125 };
> cmsCIELab Lab2 = { 50, -10, 12 };
>
> cmsUInt8Number gamut;
> cmsDoTransform(xfrm, &Lab, &gamut, 1); // Gives the alarm != 0
> cmsDoTransform(xfrm, &Lab2, &gamut, 1); // Gives 0
>
> That should work as you expect.
>
> Regards
> Matri
>
> Quoting Martin Florek <mflo...@gmail.com>:
>
>> I would like to check if a Lab color is within an ICC profile's gamut.
>> For this I create a proofing transform, but I get an error "Couldn't
>> link the profiles". I create the transform like this:
>>
>> cmsCreateProofingTransform(cmsCreateLab4Profile(), TYPE_Lab_DBL,
>> outProfile, TYPE_RGB_DBL, cmsCreateNULLProfile(),
>> INTENT_RELATIVE_COLORIMETRIC, INTENT_ABSOLUTE_COLORIMETRIC,
>> cmsFLAGS_GAMUTCHECK | cmsFLAG_SOFTPROOFING);
>>
>> When I create a normal transform from the custom Lab and the outProfile
>> (loaded from an ICC profile file), the conversion works perfectly. I set
>> the alarm codes to 0xffff before creating a proofing transform.
>>
>> What am I doing wrong? Another question about out of gamut values, is
>> there a way to get unbounded results from a transform (or multi profile
>> transform) so I could check if the colour is out of gamut when RGB
>> values are smaller than zero and bigger than 1, without the need of a
>> proofing profile? Thank you.
>> Regards,
>>
>>
>> Martin
>>
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