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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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