//--------------------------------------------------------------------------------- // // Little Color Management System // Copyright (c) 1998-2010 Marti Maria Saguer // // Permission is hereby granted, free of charge, to any person obtaining // a copy of this software and associated documentation files (the "Software"), // to deal in the Software without restriction, including without limitation // the rights to use, copy, modify, merge, publish, distribute, sublicense, // and/or sell copies of the Software, and to permit persons to whom the Software // is furnished to do so, subject to the following conditions: // // The above copyright notice and this permission notice shall be included in // all copies or substantial portions of the Software. // // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO // THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. // //--------------------------------------------------------------------------------- // #include "lcms2_internal.h" // This file contains routines for resampling and LUT optimization, black point detection // and black preservation. // Black point detection ------------------------------------------------------------------------- // PCS -> PCS round trip transform, always uses relative intent on the device -> pcs static cmsHTRANSFORM CreateRoundtripXForm(cmsHPROFILE hProfile, cmsUInt32Number nIntent) { cmsHPROFILE hLab = cmsCreateLab4Profile(NULL); cmsHTRANSFORM xform; cmsBool BPC[4] = { FALSE, FALSE, FALSE, FALSE }; cmsFloat64Number States[4] = { 1.0, 1.0, 1.0, 1.0 }; cmsHPROFILE hProfiles[4]; cmsUInt32Number Intents[4]; cmsContext ContextID = cmsGetProfileContextID(hProfile); hProfiles[0] = hLab; hProfiles[1] = hProfile; hProfiles[2] = hProfile; hProfiles[3] = hLab; Intents[0] = INTENT_RELATIVE_COLORIMETRIC; Intents[1] = nIntent; Intents[2] = INTENT_RELATIVE_COLORIMETRIC; Intents[3] = INTENT_RELATIVE_COLORIMETRIC; xform = cmsCreateExtendedTransform(ContextID, 4, hProfiles, BPC, Intents, States, NULL, 0, TYPE_Lab_DBL, TYPE_Lab_DBL, cmsFLAGS_NOCACHE|cmsFLAGS_NOOPTIMIZE); cmsCloseProfile(hLab); return xform; } // Use darker colorants to obtain black point. This works in the relative colorimetric intent and // assumes more ink results in darker colors. No ink limit is assumed. static cmsBool BlackPointAsDarkerColorant(cmsHPROFILE hInput, cmsUInt32Number Intent, cmsCIEXYZ* BlackPoint, cmsUInt32Number dwFlags) { cmsUInt16Number *Black; cmsHTRANSFORM xform; cmsColorSpaceSignature Space; cmsUInt32Number nChannels; cmsUInt32Number dwFormat; cmsHPROFILE hLab; cmsCIELab Lab; cmsCIEXYZ BlackXYZ; cmsContext ContextID = cmsGetProfileContextID(hInput); // If the profile does not support input direction, assume Black point 0 if (!cmsIsIntentSupported(hInput, Intent, LCMS_USED_AS_INPUT)) { BlackPoint -> X = BlackPoint ->Y = BlackPoint -> Z = 0.0; return FALSE; } // Create a formatter which has n channels and floating point dwFormat = cmsFormatterForColorspaceOfProfile(hInput, 2, FALSE); // Try to get black by using black colorant Space = cmsGetColorSpace(hInput); // This function returns darker colorant in 16 bits for several spaces if (!_cmsEndPointsBySpace(Space, NULL, &Black, &nChannels)) { BlackPoint -> X = BlackPoint ->Y = BlackPoint -> Z = 0.0; return FALSE; } if (nChannels != T_CHANNELS(dwFormat)) { BlackPoint -> X = BlackPoint ->Y = BlackPoint -> Z = 0.0; return FALSE; } // Lab will be used as the output space, but lab2 will avoid recursion hLab = cmsCreateLab2ProfileTHR(ContextID, NULL); if (hLab == NULL) { BlackPoint -> X = BlackPoint ->Y = BlackPoint -> Z = 0.0; return FALSE; } // Create the transform xform = cmsCreateTransformTHR(ContextID, hInput, dwFormat, hLab, TYPE_Lab_DBL, Intent, cmsFLAGS_NOOPTIMIZE|cmsFLAGS_NOCACHE); cmsCloseProfile(hLab); if (xform == NULL) { // Something went wrong. Get rid of open resources and return zero as black BlackPoint -> X = BlackPoint ->Y = BlackPoint -> Z = 0.0; return FALSE; } // Convert black to Lab cmsDoTransform(xform, Black, &Lab, 1); // Force it to be neutral, clip to max. L* of 50 Lab.a = Lab.b = 0; if (Lab.L > 50) Lab.L = 50; // Free the resources cmsDeleteTransform(xform); // Convert from Lab (which is now clipped) to XYZ. cmsLab2XYZ(NULL, &BlackXYZ, &Lab); if (BlackPoint != NULL) *BlackPoint = BlackXYZ; return TRUE; cmsUNUSED_PARAMETER(dwFlags); } // Get a black point of output CMYK profile, discounting any ink-limiting embedded // in the profile. For doing that, we use perceptual intent in input direction: // Lab (0, 0, 0) -> [Perceptual] Profile -> CMYK -> [Rel. colorimetric] Profile -> Lab static cmsBool BlackPointUsingPerceptualBlack(cmsCIEXYZ* BlackPoint, cmsHPROFILE hProfile) { cmsHTRANSFORM hRoundTrip; cmsCIELab LabIn, LabOut; cmsCIEXYZ BlackXYZ; // Is the intent supported by the profile? if (!cmsIsIntentSupported(hProfile, INTENT_PERCEPTUAL, LCMS_USED_AS_INPUT)) { BlackPoint -> X = BlackPoint ->Y = BlackPoint -> Z = 0.0; return TRUE; } hRoundTrip = CreateRoundtripXForm(hProfile, INTENT_PERCEPTUAL); if (hRoundTrip == NULL) { BlackPoint -> X = BlackPoint ->Y = BlackPoint -> Z = 0.0; return FALSE; } LabIn.L = LabIn.a = LabIn.b = 0; cmsDoTransform(hRoundTrip, &LabIn, &LabOut, 1); // Clip Lab to reasonable limits if (LabOut.L > 50) LabOut.L = 50; LabOut.a = LabOut.b = 0; cmsDeleteTransform(hRoundTrip); // Convert it to XYZ cmsLab2XYZ(NULL, &BlackXYZ, &LabOut); if (BlackPoint != NULL) *BlackPoint = BlackXYZ; return TRUE; } // This function shouldn't exist at all -- there is such quantity of broken // profiles on black point tag, that we must somehow fix chromaticity to // avoid huge tint when doing Black point compensation. This function does // just that. There is a special flag for using black point tag, but turned // off by default because it is bogus on most profiles. The detection algorithm // involves to turn BP to neutral and to use only L component. cmsBool CMSEXPORT cmsDetectBlackPoint(cmsCIEXYZ* BlackPoint, cmsHPROFILE hProfile, cmsUInt32Number Intent, cmsUInt32Number dwFlags) { // Zero for black point if (cmsGetDeviceClass(hProfile) == cmsSigLinkClass) { 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; } #ifdef CMS_USE_PROFILE_BLACK_POINT_TAG // v2, v4 rel/abs colorimetric if (cmsIsTag(hProfile, cmsSigMediaBlackPointTag) && Intent == INTENT_RELATIVE_COLORIMETRIC) { cmsCIEXYZ *BlackPtr, BlackXYZ, UntrustedBlackPoint, TrustedBlackPoint, MediaWhite; cmsCIELab Lab; // If black point is specified, then use it, BlackPtr = cmsReadTag(hProfile, cmsSigMediaBlackPointTag); if (BlackPtr != NULL) { BlackXYZ = *BlackPtr; _cmsReadMediaWhitePoint(&MediaWhite, hProfile); // Black point is absolute XYZ, so adapt to D50 to get PCS value cmsAdaptToIlluminant(&UntrustedBlackPoint, &MediaWhite, cmsD50_XYZ(), &BlackXYZ); // Force a=b=0 to get rid of any chroma cmsXYZ2Lab(NULL, &Lab, &UntrustedBlackPoint); Lab.a = Lab.b = 0; if (Lab.L > 50) Lab.L = 50; // Clip to L* <= 50 cmsLab2XYZ(NULL, &TrustedBlackPoint, &Lab); if (BlackPoint != NULL) *BlackPoint = TrustedBlackPoint; return TRUE; } } #endif // That is about v2 profiles. // If output profile, discount ink-limiting and that's all if (Intent == INTENT_RELATIVE_COLORIMETRIC && (cmsGetDeviceClass(hProfile) == cmsSigOutputClass) && (cmsGetColorSpace(hProfile) == cmsSigCmykData)) return BlackPointUsingPerceptualBlack(BlackPoint, hProfile); // Nope, compute BP using current intent. return BlackPointAsDarkerColorant(hProfile, Intent, BlackPoint, dwFlags); } // --------------------------------------------------------------------------------------------------------- // Least Squares Fit of a Quadratic Curve to Data // http://www.personal.psu.edu/jhm/f90/lectures/lsq2.html static cmsFloat64Number RootOfLeastSquaresFitQuadraticCurve(int n, cmsFloat64Number x[], cmsFloat64Number y[]) { double sum_x = 0, sum_x2 = 0, sum_x3 = 0, sum_x4 = 0; double sum_y = 0, sum_yx = 0, sum_yx2 = 0; double disc; int i; cmsMAT3 m; cmsVEC3 v, res; if (n < 4) return 0; for (i=0; i < n; i++) { double xn = x[i]; double yn = y[i]; sum_x += xn; sum_x2 += xn*xn; sum_x3 += xn*xn*xn; sum_x4 += xn*xn*xn*xn; sum_y += yn; sum_yx += yn*xn; sum_yx2 += yn*xn*xn; } _cmsVEC3init(&m.v[0], n, sum_x, sum_x2); _cmsVEC3init(&m.v[1], sum_x, sum_x2, sum_x3); _cmsVEC3init(&m.v[2], sum_x2, sum_x3, sum_x4); _cmsVEC3init(&v, sum_y, sum_yx, sum_yx2); if (!_cmsMAT3solve(&res, &m, &v)) return 0; // y = t x2 + u x + c // x = ( - u + Sqrt( u^2 - 4 t c ) ) / ( 2 t ) disc = res.n[1]*res.n[1] - 4.0 * res.n[0] * res.n[2]; if (disc < 0) return -1; return ( -1.0 * res.n[1] + sqrt( disc )) / (2.0 * res.n[0]); } static cmsBool IsMonotonic(int n, const cmsFloat64Number Table[]) { int i; cmsFloat64Number last; last = Table[n-1]; for (i = n-2; i >= 0; --i) { if (Table[i] > last) return FALSE; else last = Table[i]; } return TRUE; } // 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 = RootOfLeastSquaresFitQuadraticCurve(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; }