[gimp/gimp-2-10] plug-ins: fix #4176 color displayed wrong in multi page tiffs with linear TRC.

[Jacob Boerema <jboerema src gnome org>]

commit dbf41dc63f3d0e0c0d8c4edb61c2a46bc27c89dd
Author: Jacob Boerema <jgboerema gmail com>
Date:   Wed Dec 16 17:56:18 2020 -0500

    plug-ins: fix #4176 color displayed wrong in multi page tiffs with linear TRC.
    
    If we were loading multi page tif images as layers then only the tif pages
    that had a color profile attached would get set as linear (and each tiff page
    can have a color profile). Since most of the time only the first page has a
    color profile this caused us to load linear tiff pages incorrectly.
    
    Also we were overwriting the color profile if there was more than one since
    GIMP can only load one per image. Instead of using the last one we see
    use the first one and notify if we encounter more than one.
    
    (cherry picked from commit c05abcefc6514c70bea0fbde9e180931e30c56ca)
    
    # Conflicts:
    #       plug-ins/file-tiff/file-tiff-load.c

 plug-ins/file-tiff/file-tiff-load.c | 37 +++++++++++++++++++++++++++++++++----
 1 file changed, 33 insertions(+), 4 deletions(-)
---
diff --git a/plug-ins/file-tiff/file-tiff-load.c b/plug-ins/file-tiff/file-tiff-load.c
index ffac8e1046..b77e6b756e 100644
--- a/plug-ins/file-tiff/file-tiff-load.c
+++ b/plug-ins/file-tiff/file-tiff-load.c
@@ -183,6 +183,7 @@ load_image (GFile        *file,
   gint               min_col          = G_MAXINT;
   gint               max_row          = 0;
   gint               max_col          = 0;
+  GimpColorProfile  *first_profile      = NULL;
   gint               li;
 
   *image = 0;
@@ -393,12 +394,38 @@ load_image (GFile        *file,
       TIFFGetFieldDefaulted (tif, TIFFTAG_SAMPLEFORMAT, &sampleformat);
 
       profile = load_profile (tif);
+      if (! profile && first_profile)
+        {
+          profile = first_profile;
+          g_object_ref (profile);
+        }
+
       if (profile)
         {
+          profile_linear = gimp_color_profile_is_linear (profile);
+
+          if (! first_profile)
+            {
+              first_profile = profile;
+              g_object_ref (first_profile);
+
+              if (profile_linear && li > 0 && pages.target != GIMP_PAGE_SELECTOR_TARGET_IMAGES)
+                g_message (_("This image has a linear color profile but "
+                             "it was not set on the first layer. "
+                             "The layers below layer # %d will be "
+                             "interpreted as non linear."), li+1);
+            }
+          else if (pages.target != GIMP_PAGE_SELECTOR_TARGET_IMAGES &&
+                   ! gimp_color_profile_is_equal (first_profile, profile))
+            {
+              g_message (_("This image has multiple color profiles. "
+                           "We will use the first one. If this leads "
+                           "to incorrect results you should consider "
+                           "loading each layer as a separate image."));
+            }
+
           if (! *image)
             *profile_loaded = TRUE;
-
-          profile_linear = gimp_color_profile_is_linear (profile);
         }
 
       if (bps > 8 && bps != 8 && bps != 16 && bps != 32 && bps != 64)
@@ -901,10 +928,11 @@ load_image (GFile        *file,
         }
 
       /* attach color profile */
-
       if (profile)
         {
-          gimp_image_set_color_profile (*image, profile);
+          if (pages.target == GIMP_PAGE_SELECTOR_TARGET_IMAGES || profile == first_profile)
+            gimp_image_set_color_profile (*image, profile);
+
           g_object_unref (profile);
         }
 
@@ -1368,6 +1396,7 @@ load_image (GFile        *file,
 
       gimp_progress_update (1.0);
     }
+  g_clear_object (&first_profile);
 
   if (pages.target == GIMP_PAGE_SELECTOR_TARGET_IMAGES)
     {