a preliminar implementation of OkLab color space as built-in profile

Oklab is an alternative to CIE Lab. It works with the same logic, but claims to be more perceptually uniform than CIELab. Thanks to Lukas Sommer for the idea and Björn Ottosson for the documentation
mm2 · May 15, 2023 · f4e9f91 · f4e9f91
1 parent cdf9635
commit f4e9f91
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diff --git a/include/lcms2.h b/include/lcms2.h
@@ -1634,6 +1634,8 @@ CMSAPI cmsHPROFILE      CMSEXPORT cmsCreateXYZProfile(void);
 CMSAPI cmsHPROFILE      CMSEXPORT cmsCreate_sRGBProfileTHR(cmsContext ContextID);
 CMSAPI cmsHPROFILE      CMSEXPORT cmsCreate_sRGBProfile(void);
 
+CMSAPI cmsHPROFILE      CMSEXPORT cmsCreate_OkLabProfile(cmsContext ctx);
+
 CMSAPI cmsHPROFILE      CMSEXPORT cmsCreateBCHSWabstractProfileTHR(cmsContext ContextID,
                                                              cmsUInt32Number nLUTPoints,
                                                              cmsFloat64Number Bright,

diff --git a/src/cmsvirt.c b/src/cmsvirt.c
@@ -672,6 +672,117 @@ cmsHPROFILE CMSEXPORT cmsCreate_sRGBProfile(void)
     return cmsCreate_sRGBProfileTHR(NULL);
 }
 
+/**
+* Oklab colorspace profile (experimental)
+* 
+* This virtual profile cannot be saved as an ICC file
+*/
+cmsHPROFILE cmsCreate_OkLabProfile(cmsContext ctx)
+{
+    cmsStage* XYZPCS = _cmsStageNormalizeFromXyzFloat(ctx);
+    cmsStage* PCSXYZ = _cmsStageNormalizeToXyzFloat(ctx);
+
+    const double M_D65_D50[] =
+    {
+       1.047886, 0.022919, -0.050216,
+       0.029582, 0.990484, -0.017079,
+      -0.009252, 0.015073,  0.751678
+    };
+
+    const double M_D50_D65[] =
+    {
+         0.955513,  -0.0230732, 0.063309,
+        -0.0283249,  1.00994,   0.0210548,
+         0.0123289, -0.0205358, 1.33071
+    };
+
+    cmsStage* D65toD50 = cmsStageAllocMatrix(ctx, 3, 3, M_D65_D50, NULL);
+    cmsStage* D50toD65 = cmsStageAllocMatrix(ctx, 3, 3, M_D50_D65, NULL);
+
+    const double M_D65_LMS[] =
+    {
+        0.8189330101, 0.3618667424, -0.1288597137,
+        0.0329845436, 0.9293118715,  0.0361456387,
+        0.0482003018, 0.2643662691,  0.6338517070
+    };
+
+    const double M_LMS_D65[] =
+    {
+        1.22701,   -0.5578,   0.281256,
+       -0.0405802,  1.11226, -0.0716767,
+       -0.0763813, -0.421482, 1.58616
+    };
+
+    cmsStage* D65toLMS = cmsStageAllocMatrix(ctx, 3, 3, M_D65_LMS, NULL);
+    cmsStage* LMStoD65 = cmsStageAllocMatrix(ctx, 3, 3, M_LMS_D65, NULL);
+
+    cmsToneCurve* CubeRoot = cmsBuildGamma(ctx, 1.0 / 3.0);
+    cmsToneCurve* Cube    = cmsBuildGamma(ctx,  3.0);
+
+    cmsToneCurve* Roots[3] = { CubeRoot, CubeRoot, CubeRoot };
+    cmsToneCurve* Cubes[3] = { Cube, Cube, Cube };
+
+    cmsStage* NonLinearityFw = cmsStageAllocToneCurves(ctx, 3, Roots);
+    cmsStage* NonLinearityRv = cmsStageAllocToneCurves(ctx, 3, Cubes);
+
+    const double M_LMSprime_OkLab[] =
+    {
+        0.2104542553,  0.7936177850, -0.0040720468,
+        1.9779984951, -2.4285922050,  0.4505937099,
+        0.0259040371,  0.7827717662, -0.8086757660
+    };
+
+    const double M_OkLab_LMSprime[] =
+    {
+        1.0,  0.396338,   0.215804,
+        1.0, -0.105561,  -0.0638542,
+        1.0, -0.0894842, -1.29149
+    };
+
+    cmsStage* LMSprime_OkLab = cmsStageAllocMatrix(ctx, 3, 3, M_LMSprime_OkLab, NULL);
+    cmsStage* OkLab_LMSprime = cmsStageAllocMatrix(ctx, 3, 3, M_OkLab_LMSprime, NULL);
+
+    cmsPipeline* AToB = cmsPipelineAlloc(ctx, 3, 3);
+    cmsPipeline* BToA = cmsPipelineAlloc(ctx, 3, 3);
+
+    cmsHPROFILE hProfile = cmsCreateProfilePlaceholder(ctx);
+
+    cmsSetProfileVersion(hProfile, 4.4);
+
+    cmsSetDeviceClass(hProfile, cmsSigColorSpaceClass);
+    cmsSetColorSpace(hProfile, cmsSig3colorData);
+    cmsSetPCS(hProfile, cmsSigXYZData);
+
+    cmsSetHeaderRenderingIntent(hProfile, INTENT_RELATIVE_COLORIMETRIC);
+
+    /**
+    * Conversion PCS (XYZ/D50) to OkLab 
+    */
+    cmsPipelineInsertStage(BToA, cmsAT_END, PCSXYZ);
+    cmsPipelineInsertStage(BToA, cmsAT_END, D50toD65);
+    cmsPipelineInsertStage(BToA, cmsAT_END, D65toLMS);
+    cmsPipelineInsertStage(BToA, cmsAT_END, NonLinearityFw);
+    cmsPipelineInsertStage(BToA, cmsAT_END, LMSprime_OkLab);
+
+    cmsWriteTag(hProfile, cmsSigBToA0Tag, BToA);
+
+    cmsPipelineInsertStage(AToB, cmsAT_END, OkLab_LMSprime);
+    cmsPipelineInsertStage(AToB, cmsAT_END, NonLinearityRv);
+    cmsPipelineInsertStage(AToB, cmsAT_END, LMStoD65);
+    cmsPipelineInsertStage(AToB, cmsAT_END, D65toD50);
+    cmsPipelineInsertStage(AToB, cmsAT_END, XYZPCS);
+
+    cmsWriteTag(hProfile, cmsSigAToB0Tag, AToB);
+
+    cmsPipelineFree(BToA);
+    cmsPipelineFree(AToB);
+
+    cmsFreeToneCurve(CubeRoot);
+    cmsFreeToneCurve(Cube);
+
+    return hProfile;
+}
+
 
 
 typedef struct {
@@ -1062,9 +1173,9 @@ const cmsAllowedLUT* FindCombination(const cmsPipeline* Lut, cmsBool IsV4, cmsTa
 cmsHPROFILE CMSEXPORT cmsTransform2DeviceLink(cmsHTRANSFORM hTransform, cmsFloat64Number Version, cmsUInt32Number dwFlags)
 {
     cmsHPROFILE hProfile = NULL;
-	cmsUInt32Number FrmIn, FrmOut;
-	cmsInt32Number ChansIn, ChansOut;
-	int ColorSpaceBitsIn, ColorSpaceBitsOut;
+    cmsUInt32Number FrmIn, FrmOut;
+    cmsInt32Number ChansIn, ChansOut;
+    int ColorSpaceBitsIn, ColorSpaceBitsOut;
     _cmsTRANSFORM* xform = (_cmsTRANSFORM*) hTransform;
     cmsPipeline* LUT = NULL;
     cmsStage* mpe;

diff --git a/testbed/testcms2.c b/testbed/testcms2.c
@@ -8374,6 +8374,52 @@ int Check_sRGB_Rountrips(void)
     return 1;
 }
 
+/**
+* Check OKLab colorspace
+*/
+static
+int Check_OkLab(void)
+{
+    cmsHPROFILE hOkLab = cmsCreate_OkLabProfile(NULL);
+    cmsHPROFILE hXYZ = cmsCreateXYZProfile();
+    cmsCIEXYZ xyz, xyz2;
+    cmsCIELab okLab;
+
+#define TYPE_OKLAB_DBL          (FLOAT_SH(1)|COLORSPACE_SH(PT_MCH3)|CHANNELS_SH(3)|BYTES_SH(0))
+
+    cmsHTRANSFORM xform  = cmsCreateTransform(hXYZ, TYPE_XYZ_DBL,  hOkLab, TYPE_OKLAB_DBL, INTENT_RELATIVE_COLORIMETRIC, 0);
+    cmsHTRANSFORM xform2 = cmsCreateTransform(hOkLab, TYPE_OKLAB_DBL, hXYZ, TYPE_XYZ_DBL,  INTENT_RELATIVE_COLORIMETRIC, 0);
+
+    /**
+    * D50 should be converted to white by PCS definition
+    */
+    xyz.X = 0.9642; xyz.Y = 1.0000; xyz.Z = 0.8249;
+    cmsDoTransform(xform, &xyz, &okLab, 1);
+    cmsDoTransform(xform2, &okLab, &xyz2, 1);
+
+
+    xyz.X = 1.0; xyz.Y = 0.0; xyz.Z = 0.0;
+    cmsDoTransform(xform, &xyz, &okLab, 1);
+    cmsDoTransform(xform2, &okLab, &xyz2, 1);
+
+
+    xyz.X = 0.0; xyz.Y = 1.0; xyz.Z = 0.0;
+    cmsDoTransform(xform, &xyz, &okLab, 1);
+    cmsDoTransform(xform2, &okLab, &xyz2, 1);
+
+    xyz.X = 0.0; xyz.Y = 0.0; xyz.Z = 1.0;
+    cmsDoTransform(xform, &xyz, &okLab, 1);
+    cmsDoTransform(xform2, &okLab, &xyz2, 1);
+
+
+    cmsDeleteTransform(xform);
+    cmsDeleteTransform(xform2);
+    cmsCloseProfile(hOkLab);
+    cmsCloseProfile(hXYZ);
+
+    return 0;
+}
+
 static
 cmsHPROFILE createRgbGamma(cmsFloat64Number g)
 {
@@ -9492,6 +9538,7 @@ int main(int argc, char* argv[])
     Check("Proofing intersection", CheckProofingIntersection);
     Check("Empty MLUC", CheckEmptyMLUC);
     Check("sRGB round-trips", Check_sRGB_Rountrips);
+    Check("OkLab color space", Check_OkLab);
     Check("Gamma space detection", CheckGammaSpaceDetection);
     Check("Unbounded mode w/ integer output", CheckIntToFloatTransform);
     Check("Corrupted built-in by using cmsWriteRawTag", CheckInducedCorruption);