[Lcms-user] Check Out-of-gamut in Output CMYK Profile

[Sapaico-Valera, R. <ric...@oc...>]

Hello,

I have an output CMYK ICC profile, which I created using a printing RIP software.

Using MATLAB, I can verify that in the ICC Profile Header:
Device Class='output'
ColorSpace='CMYK'
ConnectionSpace='Lab
RenderingIntent = 'Perceptual'
Version='4.0.0'
Also, when I take a look at the 'CLUT' structures in the Profile, I can see that they are in the uint16 format.

Using an ICC profile viewer, I am able to find out whether a Lab value is inside or outside the gamut.
However, I would like to test programmatically whether a list (~1000) of Lab values is inside or outside the gamut.
>From what I found in the mailing list, I am using the following code:

---------------------------------------------------
cmsHPROFILE hInProfile, hNULL;
cmsHTRANSFORM xform;

cmsUInt16Number Alarm[16] = { 0xFF, 0xFF, 0xFF };
cmsSetAlarmCodes(Alarm);

hInProfile = cmsOpenProfileFromFile("MyICCProfile.icc", "r");
if (hInProfile == NULL) return 0;  // Failed

hNULL = cmsCreateNULLProfile();

xform = cmsCreateProofingTransform(
        hInProfile,                                         // Input
        TYPE_CMYK_16,                             // Input Format
        hNULL,                                              // Output
        TYPE_GRAY_8,                              // Output Format
        cmsCreate_sRGBProfile(),       // Proofing
        INTENT_RELATIVE_COLORIMETRIC,                       // Intent
        INTENT_RELATIVE_COLORIMETRIC,                       // Proofing Intent
        cmsFLAGS_GAMUTCHECK                                 // Flags
    );

cmsCIELab Lab1 = { 83.53, 5.35, 15.22 };
cmsCIELab Lab2 = { 12.75, -6.35, -2.32 };

cmsUInt8Number gamut;
cmsDoTransform(xform, &Lab1, &gamut, 1);
cmsDoTransform(xform, &Lab2, &gamut, 1);

cmsDeleteTransform(xform);
cmsCloseProfile(hInProfile);
cmsCloseProfile(hNULL);
---------------------------------------------------

Using the Profile Gamut viewer, I know that the value 'Lab1' is inside, and 'Lab2' is outside.
However, when I ran the code above, I get both of them as inside.
Next, I thought maybe if I changed the input to cmsDoTransform to be the corresponding CMYK values it might work:

---------------------------------------------------
cmsUInt16Number CMYK1[4], CMYK2[4];
CMYK1[0] = 6553; CMYK1[1] = 13107; CMYK1[2] = 19660; CMYK1[3] = 0;                // C=10%, M=20%, Y=30%, K=0%   -> should be in-gamut
CMYK2[0] = 52428; CMYK2[1] = 42597; CMYK2[2] = 42597; CMYK2[3] = 39321;    // C=80%, M=65%, Y=65%, K=60%   -> should be out-of-gamut
---------------------------------------------------

But it didn't help, and I still get "gamut=0" for both CMYK values (I even tried with extreme values as C=M=Y=K=0% and C=M=Y=K=100%, to no avail).

I did some debugging and I found something it might help.
In 'cmslut.c', in the "_LUTeval16" function (lines 1294..1314), the variable "lut->InputChannels" is 3;
however, I was expecting it to be 4, since I'm working with CMYK values.
Moreover, the correct 16-bit CMYK values are stored in the variable In[].

Could you please let me know what I am doing wrong?
I have the suspicion that my input to the 'cmsDoTransform' might not be ok; but I cannot figure it out what else I could try.

Thank you very much in advance for your help.

Best regards,
Ricardo Sapaico
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