bool LcmsColorProfileContainer::init()
{
    if (d->profile) cmsCloseProfile(d->profile);

    d->profile = cmsOpenProfileFromMem((void*)d->data->rawData().constData(), d->data->rawData().size());

#ifndef NDEBUG
    if (d->data->rawData().size() == 4096) {
        warnPigment << "Profile has a size of 4096, which is suspicious and indicates a possible misuse of QIODevice::read(int), check your code.";
    }
#endif

    if (d->profile) {
        wchar_t buffer[_BUFFER_SIZE_];
        d->colorSpaceSignature = cmsGetColorSpace(d->profile);
        d->deviceClass = cmsGetDeviceClass(d->profile);
        cmsGetProfileInfo(d->profile, cmsInfoDescription, cmsNoLanguage, cmsNoCountry, buffer, _BUFFER_SIZE_);
        d->productDescription = QString::fromWCharArray(buffer);
        d->valid = true;
        cmsGetProfileInfo(d->profile, cmsInfoModel, cmsNoLanguage, cmsNoCountry, buffer, _BUFFER_SIZE_);
        d->name = QString::fromWCharArray(buffer);

        cmsGetProfileInfo(d->profile, cmsInfoManufacturer, cmsNoLanguage, cmsNoCountry, buffer, _BUFFER_SIZE_);
        d->manufacturer = QString::fromWCharArray(buffer);

        // Check if the profile can convert (something->this)
        d->suitableForOutput = cmsIsMatrixShaper(d->profile)
                               || ( cmsIsCLUT(d->profile, INTENT_PERCEPTUAL, LCMS_USED_AS_INPUT) &&
                                    cmsIsCLUT(d->profile, INTENT_PERCEPTUAL, LCMS_USED_AS_OUTPUT) );
        return true;
    }
    return false;
}
Exemple #2
0
/**
 * gimp_color_profile_is_linear:
 * @profile: a #GimpColorProfile
 *
 * This function determines is the ICC profile represented by a GimpColorProfile
 * is a linear RGB profile or not, some profiles that are LUTs though linear
 * will also return FALSE;
 *
 * Return value: %TRUE if the profile is a matrix shaping profile with linear
 * TRCs, %FALSE otherwise.
 *
 * Since: 2.10
 **/
gboolean
gimp_color_profile_is_linear (GimpColorProfile *profile)
{
  cmsHPROFILE prof;
  cmsToneCurve *curve;

  g_return_val_if_fail (GIMP_IS_COLOR_PROFILE (profile), FALSE);

  prof = profile->priv->lcms_profile;

  if (! cmsIsMatrixShaper (prof))
    return FALSE;

  if (cmsIsCLUT (prof, INTENT_PERCEPTUAL, LCMS_USED_AS_INPUT))
    return FALSE;

  if (cmsIsCLUT (prof, INTENT_PERCEPTUAL, LCMS_USED_AS_OUTPUT))
    return FALSE;

  curve = cmsReadTag(prof, cmsSigRedTRCTag);
  if (curve == NULL || ! cmsIsToneCurveLinear (curve))
    return FALSE;

  curve = cmsReadTag (prof, cmsSigGreenTRCTag);
  if (curve == NULL || ! cmsIsToneCurveLinear (curve))
    return FALSE;

  curve = cmsReadTag (prof, cmsSigBlueTRCTag);
  if (curve == NULL || ! cmsIsToneCurveLinear (curve))
    return FALSE;

  return TRUE;
}
Exemple #3
0
// Return info about supported intents
cmsBool  CMSEXPORT cmsIsIntentSupported(cmsHPROFILE hProfile,
                                        cmsUInt32Number Intent, cmsUInt32Number UsedDirection)
{

    if (cmsIsCLUT(hProfile, Intent, UsedDirection)) return TRUE;

    // Is there any matrix-shaper? If so, the intent is supported. This is a bit odd, since V2 matrix shaper
    // does not fully support relative colorimetric because they cannot deal with non-zero black points, but
    // many profiles claims that, and this is certainly not true for V4 profiles. Lets answer "yes" no matter
    // the accuracy would be less than optimal in rel.col and v2 case.

    return cmsIsMatrixShaper(hProfile);
}
bool LcmsColorProfileContainer::init()
{
    if (d->profile) {
        cmsCloseProfile(d->profile);
    }

    d->profile = cmsOpenProfileFromMem((void *)d->data->rawData().constData(), d->data->rawData().size());

#ifndef NDEBUG
    if (d->data->rawData().size() == 4096) {
        qWarning() << "Profile has a size of 4096, which is suspicious and indicates a possible misuse of QIODevice::read(int), check your code.";
    }
#endif

    if (d->profile) {
        wchar_t buffer[_BUFFER_SIZE_];
        d->colorSpaceSignature = cmsGetColorSpace(d->profile);
        d->deviceClass = cmsGetDeviceClass(d->profile);
        cmsGetProfileInfo(d->profile, cmsInfoDescription, cmsNoLanguage, cmsNoCountry, buffer, _BUFFER_SIZE_);
        d->name = QString::fromWCharArray(buffer);

        //apparantly this should give us a localised string??? Not sure about this.
        cmsGetProfileInfo(d->profile, cmsInfoModel, cmsNoLanguage, cmsNoCountry, buffer, _BUFFER_SIZE_);
        d->productDescription = QString::fromWCharArray(buffer);

        cmsGetProfileInfo(d->profile, cmsInfoManufacturer, cmsNoLanguage, cmsNoCountry, buffer, _BUFFER_SIZE_);
        d->manufacturer = QString::fromWCharArray(buffer);

        cmsGetProfileInfo(d->profile, cmsInfoCopyright, cmsNoLanguage, cmsNoCountry, buffer, _BUFFER_SIZE_);
        d->copyright = QString::fromWCharArray(buffer);

        cmsProfileClassSignature profile_class;
        profile_class = cmsGetDeviceClass(d->profile);
        d->valid = (profile_class != cmsSigNamedColorClass);

        //This is where obtain the whitepoint, and convert it to the actual white point of the profile in the case a Chromatic adaption tag is
        //present. This is necessary for profiles following the v4 spec.
        cmsCIEXYZ baseMediaWhitePoint;//dummy to hold copy of mediawhitepoint if this is modified by chromatic adaption.
        if (cmsIsTag(d->profile, cmsSigMediaWhitePointTag)) {
            d->mediaWhitePoint = *((cmsCIEXYZ *)cmsReadTag(d->profile, cmsSigMediaWhitePointTag));
            baseMediaWhitePoint = d->mediaWhitePoint;
            cmsXYZ2xyY(&d->whitePoint, &d->mediaWhitePoint);

            if (cmsIsTag(d->profile, cmsSigChromaticAdaptationTag)) {
                //the chromatic adaption tag represent a matrix from the actual white point of the profile to D50.
                cmsCIEXYZ *CAM1 = (cmsCIEXYZ *)cmsReadTag(d->profile, cmsSigChromaticAdaptationTag);
                //We first put all our data into structures we can manipulate.
                double d3dummy [3] = {d->mediaWhitePoint.X, d->mediaWhitePoint.Y, d->mediaWhitePoint.Z};
                QGenericMatrix<1, 3, double> whitePointMatrix(d3dummy);
                QTransform invertDummy(CAM1[0].X, CAM1[0].Y, CAM1[0].Z, CAM1[1].X, CAM1[1].Y, CAM1[1].Z, CAM1[2].X, CAM1[2].Y, CAM1[2].Z);
                //we then abuse QTransform's invert function because it probably does matrix invertion 20 times better than I can program.
                //if the matrix is uninvertable, invertedDummy will be an identity matrix, which for us means that it won't give any noticeble
                //effect when we start multiplying.
                QTransform invertedDummy = invertDummy.inverted();
                //we then put the QTransform into a generic 3x3 matrix.
                double d9dummy [9] = {invertedDummy.m11(), invertedDummy.m12(), invertedDummy.m13(),
                                      invertedDummy.m21(), invertedDummy.m22(), invertedDummy.m23(),
                                      invertedDummy.m31(), invertedDummy.m32(), invertedDummy.m33()
                                     };
                QGenericMatrix<3, 3, double> chromaticAdaptionMatrix(d9dummy);
                //multiplying our inverted adaption matrix with the whitepoint gives us the right whitepoint.
                QGenericMatrix<1, 3, double> result = chromaticAdaptionMatrix * whitePointMatrix;
                //and then we pour the matrix into the whitepoint variable. Generic matrix does row/column for indices even though it
                //uses column/row for initialising.
                d->mediaWhitePoint.X = result(0, 0);
                d->mediaWhitePoint.Y = result(1, 0);
                d->mediaWhitePoint.Z = result(2, 0);
                cmsXYZ2xyY(&d->whitePoint, &d->mediaWhitePoint);
            }
        }
        //This is for RGB profiles, but it only works for matrix profiles. Need to design it to work with non-matrix profiles.
        if (cmsIsTag(d->profile, cmsSigRedColorantTag)) {
            cmsCIEXYZTRIPLE tempColorants;
            tempColorants.Red = *((cmsCIEXYZ *)cmsReadTag(d->profile, cmsSigRedColorantTag));
            tempColorants.Green = *((cmsCIEXYZ *)cmsReadTag(d->profile, cmsSigGreenColorantTag));
            tempColorants.Blue = *((cmsCIEXYZ *)cmsReadTag(d->profile, cmsSigBlueColorantTag));
            //convert to d65, this is useless.
            cmsAdaptToIlluminant(&d->colorants.Red, &baseMediaWhitePoint, &d->mediaWhitePoint, &tempColorants.Red);
            cmsAdaptToIlluminant(&d->colorants.Green, &baseMediaWhitePoint, &d->mediaWhitePoint, &tempColorants.Green);
            cmsAdaptToIlluminant(&d->colorants.Blue, &baseMediaWhitePoint, &d->mediaWhitePoint, &tempColorants.Blue);
            //d->colorants = tempColorants;
            d->hasColorants = true;
        } else {
            //qDebug()<<d->name<<": has no colorants";
            d->hasColorants = false;
        }
        //retrieve TRC.
        if (cmsIsTag(d->profile, cmsSigRedTRCTag) && cmsIsTag(d->profile, cmsSigBlueTRCTag) && cmsIsTag(d->profile, cmsSigGreenTRCTag)) {

            d->redTRC = ((cmsToneCurve *)cmsReadTag (d->profile, cmsSigRedTRCTag));
            d->greenTRC = ((cmsToneCurve *)cmsReadTag (d->profile, cmsSigGreenTRCTag));
            d->blueTRC = ((cmsToneCurve *)cmsReadTag (d->profile, cmsSigBlueTRCTag));
            d->redTRCReverse = cmsReverseToneCurve(d->redTRC);
            d->greenTRCReverse = cmsReverseToneCurve(d->greenTRC);
            d->blueTRCReverse = cmsReverseToneCurve(d->blueTRC);
            d->hasTRC = true;

        } else if (cmsIsTag(d->profile, cmsSigGrayTRCTag)) {
            d->grayTRC = ((cmsToneCurve *)cmsReadTag (d->profile, cmsSigGrayTRCTag));
            d->grayTRCReverse = cmsReverseToneCurve(d->grayTRC);
            d->hasTRC = true;
        } else {
            d->hasTRC = false;
        }

        // Check if the profile can convert (something->this)
        d->suitableForOutput = cmsIsMatrixShaper(d->profile)
                               || (cmsIsCLUT(d->profile, INTENT_PERCEPTUAL, LCMS_USED_AS_INPUT) &&
                                   cmsIsCLUT(d->profile, INTENT_PERCEPTUAL, LCMS_USED_AS_OUTPUT));

        d->version = cmsGetProfileVersion(d->profile);
        d->defaultIntent = cmsGetHeaderRenderingIntent(d->profile);
        d->isMatrixShaper = cmsIsMatrixShaper(d->profile);
        d->isPerceptualCLUT = cmsIsCLUT(d->profile, INTENT_PERCEPTUAL, LCMS_USED_AS_INPUT);
        d->isSaturationCLUT = cmsIsCLUT(d->profile, INTENT_SATURATION, LCMS_USED_AS_INPUT);
        d->isAbsoluteCLUT = cmsIsCLUT(d->profile, INTENT_SATURATION, LCMS_USED_AS_INPUT);
        d->isRelativeCLUT = cmsIsCLUT(d->profile, INTENT_RELATIVE_COLORIMETRIC, LCMS_USED_AS_INPUT);

        return true;
    }

    return false;
}
Exemple #5
0
// Calculates the black point of a destination profile.
// This algorithm comes from the Adobe paper disclosing its black point compensation method.
cmsBool CMSEXPORT cmsDetectDestinationBlackPoint(cmsCIEXYZ* BlackPoint, cmsHPROFILE hProfile, cmsUInt32Number Intent, cmsUInt32Number dwFlags)
{
    cmsColorSpaceSignature ColorSpace;
    cmsHTRANSFORM hRoundTrip = NULL;
    cmsCIELab InitialLab, destLab, Lab;
    cmsFloat64Number inRamp[256], outRamp[256];
    cmsFloat64Number MinL, MaxL;
    cmsBool NearlyStraightMidrange = TRUE;  
    cmsFloat64Number yRamp[256];
    cmsFloat64Number x[256], y[256];
    cmsFloat64Number lo, hi;
    int n, l;
    cmsProfileClassSignature devClass;

    // Make sure the device class is adequate
    devClass = cmsGetDeviceClass(hProfile);
    if (devClass == cmsSigLinkClass ||
        devClass == cmsSigAbstractClass ||
        devClass == cmsSigNamedColorClass) {
            BlackPoint -> X = BlackPoint ->Y = BlackPoint -> Z = 0.0;
            return FALSE;
    }

    // Make sure intent is adequate
    if (Intent != INTENT_PERCEPTUAL &&
        Intent != INTENT_RELATIVE_COLORIMETRIC &&
        Intent != INTENT_SATURATION) {
            BlackPoint -> X = BlackPoint ->Y = BlackPoint -> Z = 0.0;
            return FALSE;
    }


    // v4 + perceptual & saturation intents does have its own black point, and it is
    // well specified enough to use it. Black point tag is deprecated in V4.
    if ((cmsGetEncodedICCversion(hProfile) >= 0x4000000) &&
        (Intent == INTENT_PERCEPTUAL || Intent == INTENT_SATURATION)) {

            // Matrix shaper share MRC & perceptual intents
            if (cmsIsMatrixShaper(hProfile))
                return BlackPointAsDarkerColorant(hProfile, INTENT_RELATIVE_COLORIMETRIC, BlackPoint, 0);

            // Get Perceptual black out of v4 profiles. That is fixed for perceptual & saturation intents
            BlackPoint -> X = cmsPERCEPTUAL_BLACK_X;
            BlackPoint -> Y = cmsPERCEPTUAL_BLACK_Y;
            BlackPoint -> Z = cmsPERCEPTUAL_BLACK_Z;
            return TRUE;
    }


    // Check if the profile is lut based and gray, rgb or cmyk (7.2 in Adobe's document)
    ColorSpace = cmsGetColorSpace(hProfile);
    if (!cmsIsCLUT(hProfile, Intent, LCMS_USED_AS_OUTPUT ) ||
        (ColorSpace != cmsSigGrayData &&
         ColorSpace != cmsSigRgbData  &&
         ColorSpace != cmsSigCmykData)) {

        // In this case, handle as input case
        return cmsDetectBlackPoint(BlackPoint, hProfile, Intent, dwFlags);
    }

    // It is one of the valid cases!, use Adobe algorithm

    
    // Set a first guess, that should work on good profiles.
    if (Intent == INTENT_RELATIVE_COLORIMETRIC) {

        cmsCIEXYZ IniXYZ;

        // calculate initial Lab as source black point
        if (!cmsDetectBlackPoint(&IniXYZ, hProfile, Intent, dwFlags)) {
            return FALSE;
        }

        // convert the XYZ to lab
        cmsXYZ2Lab(NULL, &InitialLab, &IniXYZ);

    } else {

        // set the initial Lab to zero, that should be the black point for perceptual and saturation
        InitialLab.L = 0;
        InitialLab.a = 0;
        InitialLab.b = 0;
    }


    // Step 2
    // ======

    // Create a roundtrip. Define a Transform BT for all x in L*a*b*
    hRoundTrip = CreateRoundtripXForm(hProfile, Intent);
    if (hRoundTrip == NULL)  return FALSE;

    // Compute ramps

    for (l=0; l < 256; l++) {

        Lab.L = (cmsFloat64Number) (l * 100.0) / 255.0;
        Lab.a = cmsmin(50, cmsmax(-50, InitialLab.a));
        Lab.b = cmsmin(50, cmsmax(-50, InitialLab.b));

        cmsDoTransform(hRoundTrip, &Lab, &destLab, 1);

        inRamp[l]  = Lab.L;
        outRamp[l] = destLab.L;
    }

    // Make monotonic
    for (l = 254; l > 0; --l) {
        outRamp[l] = cmsmin(outRamp[l], outRamp[l+1]);
    }

    // Check
    if (! (outRamp[0] < outRamp[255])) {

        cmsDeleteTransform(hRoundTrip);
        BlackPoint -> X = BlackPoint ->Y = BlackPoint -> Z = 0.0;
        return FALSE;
    }


    // Test for mid range straight (only on relative colorimetric)
    NearlyStraightMidrange = TRUE;
    MinL = outRamp[0]; MaxL = outRamp[255];
    if (Intent == INTENT_RELATIVE_COLORIMETRIC) {
      
        for (l=0; l < 256; l++) {

            if (! ((inRamp[l] <= MinL + 0.2 * (MaxL - MinL) ) ||   
                (fabs(inRamp[l] - outRamp[l]) < 4.0 )))
                NearlyStraightMidrange = FALSE;
        }

        // If the mid range is straight (as determined above) then the 
        // DestinationBlackPoint shall be the same as initialLab. 
        // Otherwise, the DestinationBlackPoint shall be determined 
        // using curve fitting.
        if (NearlyStraightMidrange) {

            cmsLab2XYZ(NULL, BlackPoint, &InitialLab);
            cmsDeleteTransform(hRoundTrip);
            return TRUE;
        }
    }

 
    // curve fitting: The round-trip curve normally looks like a nearly constant section at the black point,
    // with a corner and a nearly straight line to the white point.  
    for (l=0; l < 256; l++) {
    
        yRamp[l] = (outRamp[l] - MinL) / (MaxL - MinL);
    }

    // find the black point using the least squares error quadratic curve fitting
    if (Intent == INTENT_RELATIVE_COLORIMETRIC) {
        lo = 0.1;
        hi = 0.5;
    }
    else {

        // Perceptual and saturation
        lo = 0.03;
        hi = 0.25;
    }

    // Capture shadow points for the fitting.
    n = 0;
    for (l=0; l < 256; l++) {
    
        cmsFloat64Number ff = yRamp[l];

        if (ff >= lo && ff < hi) {
            x[n] = inRamp[l];
            y[n] = yRamp[l];
            n++;
        }    
    }

    
    // No suitable points
    if (n < 3 ) {
        cmsDeleteTransform(hRoundTrip);
        BlackPoint -> X = BlackPoint ->Y = BlackPoint -> Z = 0.0;
        return FALSE;
    }

  
    // fit and get the vertex of quadratic curve
    Lab.L = RootOfLeastSquaresFitQuadraticCurve(n, x, y);

    if (Lab.L < 0.0) { // clip to zero L* if the vertex is negative
        Lab.L = 0;
    }

    Lab.a = InitialLab.a;
    Lab.b = InitialLab.b;

    cmsLab2XYZ(NULL, BlackPoint, &Lab);

    cmsDeleteTransform(hRoundTrip);
    return TRUE;
}
Exemple #6
0
// Calculates the black point of a destination profile. 
// This algorithm comes from the Adobe paper disclosing its black point compensation method. 
cmsBool CMSEXPORT cmsDetectDestinationBlackPoint(cmsCIEXYZ* BlackPoint, cmsHPROFILE hProfile, cmsUInt32Number Intent, cmsUInt32Number dwFlags)
{  
    cmsColorSpaceSignature ColorSpace;
    cmsHTRANSFORM hRoundTrip = NULL;
    cmsCIELab InitialLab, destLab, Lab;
  
    cmsFloat64Number MinL, MaxL;
    cmsBool NearlyStraightMidRange = FALSE;
    cmsFloat64Number L;
    cmsFloat64Number x[101], y[101];
    cmsFloat64Number lo, hi, NonMonoMin;
    int n, l, i, NonMonoIndx;
    

    // Make sure intent is adequate
    if (Intent != INTENT_PERCEPTUAL &&
        Intent != INTENT_RELATIVE_COLORIMETRIC &&
		Intent != INTENT_SATURATION) {
			BlackPoint -> X = BlackPoint ->Y = BlackPoint -> Z = 0.0;
			return FALSE;
	}


    // v4 + perceptual & saturation intents does have its own black point, and it is 
    // well specified enough to use it. Black point tag is deprecated in V4.
    if ((cmsGetEncodedICCversion(hProfile) >= 0x4000000) &&     
        (Intent == INTENT_PERCEPTUAL || Intent == INTENT_SATURATION)) {

            // Matrix shaper share MRC & perceptual intents
            if (cmsIsMatrixShaper(hProfile)) 
                return BlackPointAsDarkerColorant(hProfile, INTENT_RELATIVE_COLORIMETRIC, BlackPoint, 0);

            // Get Perceptual black out of v4 profiles. That is fixed for perceptual & saturation intents
            BlackPoint -> X = cmsPERCEPTUAL_BLACK_X; 
            BlackPoint -> Y = cmsPERCEPTUAL_BLACK_Y;
            BlackPoint -> Z = cmsPERCEPTUAL_BLACK_Z;
            return TRUE;
    }


    // Check if the profile is lut based and gray, rgb or cmyk (7.2 in Adobe's document)
    ColorSpace = cmsGetColorSpace(hProfile);
    if (!cmsIsCLUT(hProfile, Intent, LCMS_USED_AS_OUTPUT ) ||
        (ColorSpace != cmsSigGrayData && 
         ColorSpace != cmsSigRgbData  && 
         ColorSpace != cmsSigCmykData)) { 

        // In this case, handle as input case
        return cmsDetectBlackPoint(BlackPoint, hProfile, Intent, dwFlags);
    }

    // It is one of the valid cases!, presto chargo hocus pocus, go for the Adobe magic

    // Step 1
    // ======

    // Set a first guess, that should work on good profiles.
    if (Intent == INTENT_RELATIVE_COLORIMETRIC) {

        cmsCIEXYZ IniXYZ;

        // calculate initial Lab as source black point
        if (!cmsDetectBlackPoint(&IniXYZ, hProfile, Intent, dwFlags)) {           
            return FALSE;
        }

        // convert the XYZ to lab
        cmsXYZ2Lab(NULL, &InitialLab, &IniXYZ);

    } else {

        // set the initial Lab to zero, that should be the black point for perceptual and saturation
        InitialLab.L = 0;
        InitialLab.a = 0;
        InitialLab.b = 0;
    }


    // Step 2
    // ======

    // Create a roundtrip. Define a Transform BT for all x in L*a*b*
    hRoundTrip = CreateRoundtripXForm(hProfile, Intent);
    if (hRoundTrip == NULL)  return FALSE;
    
    // Calculate Min L*
    Lab = InitialLab;
    Lab.L = 0;
    cmsDoTransform(hRoundTrip, &Lab, &destLab, 1);
    MinL = destLab.L;

    // Calculate Max L*
    Lab = InitialLab;
    Lab.L = 100;
    cmsDoTransform(hRoundTrip, &Lab, &destLab, 1);
    MaxL = destLab.L;

    // Step 3
    // ======

    // check if quadratic estimation needs to be done.  
    if (Intent == INTENT_RELATIVE_COLORIMETRIC) {

        // Conceptually, this code tests how close the source l and converted L are to one another in the mid-range
        // of the values. If the converted ramp of L values is close enough to a straight line y=x, then InitialLab 
        // is good enough to be the DestinationBlackPoint,        
        NearlyStraightMidRange = TRUE;
        
        for (l=0; l <= 100; l++) {              

            Lab.L = l;
            Lab.a = InitialLab.a;
            Lab.b = InitialLab.b;

            cmsDoTransform(hRoundTrip, &Lab, &destLab, 1);

            L = destLab.L;

            // Check the mid range in 20% after MinL
            if (L > (MinL + 0.2 * (MaxL - MinL))) {

                // Is close enough?
                if (fabs(L - l) > 4.0) {

                    // Too far away, profile is buggy!
                    NearlyStraightMidRange = FALSE;
                    break;
                }
            }           
        }
    }
    else {
        // Check is always performed for perceptual and saturation intents
        NearlyStraightMidRange = FALSE;
    }


    // If no furter checking is needed, we are done
    if (NearlyStraightMidRange) { 

        cmsLab2XYZ(NULL, BlackPoint, &InitialLab);          
        cmsDeleteTransform(hRoundTrip);
        return TRUE;
    }
    
    // The round-trip curve normally looks like a nearly constant section at the black point, 
    // with a corner and a nearly straight line to the white point.
    
    // STEP 4
    // =======

    // find the black point using the least squares error quadratic curve fitting

    if (Intent == INTENT_RELATIVE_COLORIMETRIC) {
        lo = 0.1;
        hi = 0.5;
    }
    else {

        // Perceptual and saturation
        lo = 0.03;
        hi = 0.25;
    }

    // Capture points for the fitting. 
    n = 0;
    for (l=0; l <= 100; l++) {

        cmsFloat64Number ff;

        Lab.L = (cmsFloat64Number) l;
        Lab.a = InitialLab.a;
        Lab.b = InitialLab.b;

        cmsDoTransform(hRoundTrip, &Lab, &destLab, 1);

        ff = (destLab.L - MinL)/(MaxL - MinL);

        if (ff >= lo && ff < hi) {

            x[n] = Lab.L;
            y[n] = ff;
            n++;
        }

    }

	// This part is not on the Adobe paper, but I found is necessary for getting any result.

	if (IsMonotonic(n, y)) {

		// Monotonic means lower point is stil valid
        cmsLab2XYZ(NULL, BlackPoint, &InitialLab);
        cmsDeleteTransform(hRoundTrip);
        return TRUE;
	}
	
    // No suitable points, regret and use safer algorithm
    if (n == 0) {
        cmsDeleteTransform(hRoundTrip);
        return cmsDetectBlackPoint(BlackPoint, hProfile, Intent, dwFlags);
    }


	NonMonoMin = 100;
	NonMonoIndx = 0;
	for (i=0; i < n; i++) {

		if (y[i] < NonMonoMin) {
			NonMonoIndx = i;
			NonMonoMin = y[i];
		}
	}

	Lab.L = x[NonMonoIndx];

    // fit and get the vertex of quadratic curve
    Lab.L = VertexOfLeastSquaresFitQuadraticCurve(n, x, y);

    if (Lab.L < 0.0 || Lab.L > 50.0) { // clip to zero L* if the vertex is negative
        Lab.L = 0;
    }
    
    Lab.a = InitialLab.a;
    Lab.b = InitialLab.b;

    cmsLab2XYZ(NULL, BlackPoint, &Lab);

    cmsDeleteTransform(hRoundTrip);
    return TRUE;
}