[gimp] plug-ins: Use GIMP's internal profile when loading EXR

[Tobias Ellinghaus <et src gnome org>]

commit 3d86a6c709366ab839c690185d295b6dea18836f
Author: Tobias Ellinghaus <me houz org>
Date:   Fri Apr 29 13:10:30 2016 +0200

    plug-ins: Use GIMP's internal profile when loading EXR
    
    ... when it's appropriate.

 plug-ins/file-exr/file-exr.c         |   19 ++------
 plug-ins/file-exr/openexr-wrapper.cc |   74 ++++++++++++++++++++++++++++-----
 plug-ins/file-exr/openexr-wrapper.h  |    4 +-
 3 files changed, 69 insertions(+), 28 deletions(-)
---
diff --git a/plug-ins/file-exr/file-exr.c b/plug-ins/file-exr/file-exr.c
index e9ab507..135a3c0 100644
--- a/plug-ins/file-exr/file-exr.c
+++ b/plug-ins/file-exr/file-exr.c
@@ -302,22 +302,13 @@ load_image (const gchar  *filename,
    */
   if (image_type == GIMP_RGB)
     {
-      cmsHPROFILE lcms_profile;
+      GimpColorProfile *profile;
 
-      lcms_profile = exr_loader_get_icc_profile (loader);
-      if (lcms_profile)
+      profile = exr_loader_get_profile (loader);
+      if (profile)
         {
-          GimpColorProfile *profile;
-
-          profile = gimp_color_profile_new_from_lcms_profile (lcms_profile,
-                                                              NULL);
-          cmsCloseProfile (lcms_profile);
-
-          if (profile)
-            {
-              gimp_image_set_color_profile (image, profile);
-              g_object_unref (profile);
-            }
+          gimp_image_set_color_profile (image, profile);
+          g_object_unref (profile);
         }
     }
 
diff --git a/plug-ins/file-exr/openexr-wrapper.cc b/plug-ins/file-exr/openexr-wrapper.cc
index 6637a19..ef401f8 100644
--- a/plug-ins/file-exr/openexr-wrapper.cc
+++ b/plug-ins/file-exr/openexr-wrapper.cc
@@ -7,6 +7,7 @@
  */
 #include "libgimp/gimp.h"
 #include "libgimp/gimpui.h"
+#include "libgimpcolor/gimpcolor.h"
 
 #include "openexr-wrapper.h"
 
@@ -24,6 +25,15 @@ using namespace Imf;
 using namespace Imf::RgbaYca;
 using namespace Imath;
 
+static bool XYZ_equal(cmsCIEXYZ *a, cmsCIEXYZ *b)
+{
+  static const double epsilon = 0.0001;
+  // Y is encoding the luminance, we normalize that for comparison
+  return fabs ((a->X / a->Y * b->Y) - b->X) < epsilon &&
+         fabs ((a->Y / a->Y * b->Y) - b->Y) < epsilon &&
+         fabs ((a->Z / a->Y * b->Y) - b->Z) < epsilon;
+}
+
 struct _EXRLoader
 {
   _EXRLoader(const char* filename) :
@@ -172,12 +182,20 @@ struct _EXRLoader
     return has_alpha_ ? 1 : 0;
   }
 
-  cmsHPROFILE getICCProfile() const {
+  GimpColorProfile *getProfile() const {
     Chromaticities chromaticities;
     float whiteLuminance = 1.0;
 
-    cmsHPROFILE profile = NULL;
+    GimpColorProfile *linear_srgb_profile;
+    cmsHPROFILE linear_srgb_lcms;
+
+    GimpColorProfile *profile;
+    cmsHPROFILE lcms_profile;
 
+    cmsCIEXYZ *gimp_r_XYZ, *gimp_g_XYZ, *gimp_b_XYZ, *gimp_w_XYZ;
+    cmsCIEXYZ exr_r_XYZ, exr_g_XYZ, exr_b_XYZ, exr_w_XYZ;
+
+    // get the color information from the EXR
     if (hasChromaticities (file_.header ()))
       chromaticities = Imf::chromaticities (file_.header ());
     else
@@ -195,6 +213,7 @@ struct _EXRLoader
     std::cout << "hasWhiteLuminance: "
               << hasWhiteLuminance (file_.header ())
               << std::endl;
+    std::cout << whiteLuminance << std::endl;
     std::cout << chromaticities.red << std::endl;
     std::cout << chromaticities.green << std::endl;
     std::cout << chromaticities.blue << std::endl;
@@ -202,7 +221,6 @@ struct _EXRLoader
     std::cout << std::endl;
 #endif
 
-    // TODO: maybe factor this out into libgimpcolor/gimpcolorprofile.h ?
     cmsCIExyY whitePoint = { chromaticities.white.x,
                              chromaticities.white.y,
                              whiteLuminance };
@@ -216,29 +234,61 @@ struct _EXRLoader
                                           chromaticities.blue.y,
                                           whiteLuminance } };
 
+    // get the primaries + wp from GIMP's internal linear sRGB profile
+    linear_srgb_profile = gimp_color_profile_new_rgb_srgb_linear ();
+    linear_srgb_lcms = gimp_color_profile_get_lcms_profile (linear_srgb_profile);
+
+    gimp_r_XYZ = (cmsCIEXYZ *) cmsReadTag (linear_srgb_lcms, cmsSigRedColorantTag);
+    gimp_g_XYZ = (cmsCIEXYZ *) cmsReadTag (linear_srgb_lcms, cmsSigGreenColorantTag);
+    gimp_b_XYZ = (cmsCIEXYZ *) cmsReadTag (linear_srgb_lcms, cmsSigBlueColorantTag);
+    gimp_w_XYZ = (cmsCIEXYZ *) cmsReadTag (linear_srgb_lcms, cmsSigMediaWhitePointTag);
+
+    cmsxyY2XYZ(&exr_r_XYZ, &CameraPrimaries.Red);
+    cmsxyY2XYZ(&exr_g_XYZ, &CameraPrimaries.Green);
+    cmsxyY2XYZ(&exr_b_XYZ, &CameraPrimaries.Blue);
+    cmsxyY2XYZ(&exr_w_XYZ, &whitePoint);
+
+    // ... and check if the data stored in the EXR matches GIMP's internal profile
+    bool exr_is_linear_srgb = XYZ_equal (&exr_r_XYZ, gimp_r_XYZ) &&
+                              XYZ_equal (&exr_g_XYZ, gimp_g_XYZ) &&
+                              XYZ_equal (&exr_b_XYZ, gimp_b_XYZ) &&
+                              XYZ_equal (&exr_w_XYZ, gimp_w_XYZ);
+
+    // using GIMP's linear sRGB profile allows to skip the conversion popup
+    if (exr_is_linear_srgb)
+      return linear_srgb_profile;
+
+    // nope, it's something else. Clean up and build a new profile
+    g_object_unref (linear_srgb_profile);
+
+    // TODO: maybe factor this out into libgimpcolor/gimpcolorprofile.h ?
     double Parameters[2] = { 1.0, 0.0 };
     cmsToneCurve *Gamma[3];
     Gamma[0] = Gamma[1] = Gamma[2] = cmsBuildParametricToneCurve(0,
                                                                  1,
                                                                  Parameters);
-    profile = cmsCreateRGBProfile (&whitePoint, &CameraPrimaries, Gamma);
+    lcms_profile = cmsCreateRGBProfile (&whitePoint, &CameraPrimaries, Gamma);
     cmsFreeToneCurve (Gamma[0]);
-    if (profile == NULL) return NULL;
+    if (lcms_profile == NULL) return NULL;
 
-    cmsSetProfileVersion (profile, 2.1);
+//     cmsSetProfileVersion (lcms_profile, 2.1);
     cmsMLU *mlu0 = cmsMLUalloc (NULL, 1);
     cmsMLUsetASCII (mlu0, "en", "US", "(GIMP internal)");
     cmsMLU *mlu1 = cmsMLUalloc(NULL, 1);
     cmsMLUsetASCII (mlu1, "en", "US", "color profile from EXR chromaticities");
     cmsMLU *mlu2 = cmsMLUalloc(NULL, 1);
     cmsMLUsetASCII (mlu2, "en", "US", "color profile from EXR chromaticities");
-    cmsWriteTag (profile, cmsSigDeviceMfgDescTag, mlu0);
-    cmsWriteTag (profile, cmsSigDeviceModelDescTag, mlu1);
-    cmsWriteTag (profile, cmsSigProfileDescriptionTag, mlu2);
+    cmsWriteTag (lcms_profile, cmsSigDeviceMfgDescTag, mlu0);
+    cmsWriteTag (lcms_profile, cmsSigDeviceModelDescTag, mlu1);
+    cmsWriteTag (lcms_profile, cmsSigProfileDescriptionTag, mlu2);
     cmsMLUfree (mlu0);
     cmsMLUfree (mlu1);
     cmsMLUfree (mlu2);
 
+    profile = gimp_color_profile_new_from_lcms_profile (lcms_profile,
+                                                        NULL);
+    cmsCloseProfile (lcms_profile);
+
     return profile;
   }
 
@@ -385,10 +435,10 @@ exr_loader_has_alpha (EXRLoader *loader)
   return loader->hasAlpha();
 }
 
-cmsHPROFILE
-exr_loader_get_icc_profile (EXRLoader *loader)
+GimpColorProfile *
+exr_loader_get_profile (EXRLoader *loader)
 {
-  return loader->getICCProfile ();
+  return loader->getProfile ();
 }
 
 gchar *
diff --git a/plug-ins/file-exr/openexr-wrapper.h b/plug-ins/file-exr/openexr-wrapper.h
index fcb4984..f2cf321 100644
--- a/plug-ins/file-exr/openexr-wrapper.h
+++ b/plug-ins/file-exr/openexr-wrapper.h
@@ -50,8 +50,8 @@ exr_loader_get_image_type (EXRLoader *loader);
 int
 exr_loader_has_alpha (EXRLoader *loader);
 
-cmsHPROFILE
-exr_loader_get_icc_profile (EXRLoader *loader);
+GimpColorProfile *
+exr_loader_get_profile (EXRLoader *loader);
 
 gchar *
 exr_loader_get_comment (EXRLoader *loader);