[gimp/gimp-2-10] plug-ins: implement our profile export policy for HEIF.

[Jehan <jehanp src gnome org>]

commit ae35061fababa12e670db944c3146419de424f93
Author: Jehan <jehan girinstud io>
Date:   Mon Jul 1 15:36:59 2019 +0200

    plug-ins: implement our profile export policy for HEIF.
    
    Same as WebP or jpeg: follow explicitly assigned profile TRC; convert
    default (non-assigned) profile to sRGB, except if work format is 8-bit
    linear.
    
    (cherry picked from commit 5d6baf5f85fc62cf1f577a505beaad27a11b6c19)

 plug-ins/common/file-heif.c | 57 ++++++++++++++++++++++++++++++++++++---------
 1 file changed, 46 insertions(+), 11 deletions(-)
---
diff --git a/plug-ins/common/file-heif.c b/plug-ins/common/file-heif.c
index 237213e2cc..a1c72cab10 100644
--- a/plug-ins/common/file-heif.c
+++ b/plug-ins/common/file-heif.c
@@ -672,7 +672,11 @@ save_image (GFile             *file,
   struct heif_image_handle *handle;
   struct heif_writer        writer;
   struct heif_error         err;
+#ifdef HAVE_LIBHEIF_1_4_0
   GimpColorProfile         *profile = NULL;
+  const guint8             *icc_data;
+  gsize                     icc_length;
+#endif
   GOutputStream            *output;
   GeglBuffer               *buffer;
   const Babl               *format;
@@ -681,11 +685,11 @@ save_image (GFile             *file,
   gint                      width;
   gint                      height;
   gboolean                  has_alpha;
+  gboolean                  out_linear = FALSE;
 
   gimp_progress_init_printf (_("Exporting '%s'"),
                              g_file_get_parse_name (file));
 
-  profile = gimp_image_get_effective_color_profile (image_ID);
   width   = gimp_drawable_width  (drawable_ID);
   height  = gimp_drawable_height (drawable_ID);
 
@@ -698,18 +702,39 @@ save_image (GFile             *file,
                            heif_chroma_interleaved_RGB,
                            &image);
 
-  if (profile)
-    {
 #ifdef HAVE_LIBHEIF_1_4_0
-      const guint8 *icc_data;
-      gsize         icc_length;
+  profile = gimp_image_get_color_profile (image_ID);
+  if (profile && gimp_color_profile_is_linear (profile))
+    out_linear = TRUE;
 
-      icc_data = gimp_color_profile_get_icc_profile (profile, &icc_length);
-      heif_image_set_raw_color_profile (image, "prof", icc_data, icc_length);
-#endif /* HAVE_LIBHEIF_1_4_0 */
-      g_object_unref (profile);
+  if (! profile)
+    {
+      profile = gimp_image_get_effective_color_profile (image_ID);
+
+      if (gimp_color_profile_is_linear (profile))
+        {
+          if (gimp_image_get_precision (image_ID) != GIMP_PRECISION_U8_LINEAR)
+            {
+              /* If stored data was linear, let's convert the profile. */
+              GimpColorProfile *saved_profile;
+
+              saved_profile = gimp_color_profile_new_srgb_trc_from_color_profile (profile);
+              g_clear_object (&profile);
+              profile = saved_profile;
+            }
+          else
+            {
+              /* Keep linear profile as-is for 8-bit linear image. */
+              out_linear = TRUE;
+            }
+        }
     }
 
+  icc_data = gimp_color_profile_get_icc_profile (profile, &icc_length);
+  heif_image_set_raw_color_profile (image, "prof", icc_data, icc_length);
+  g_object_unref (profile);
+#endif /* HAVE_LIBHEIF_1_4_0 */
+
   heif_image_add_plane (image, heif_channel_interleaved,
                         width, height, has_alpha ? 32 : 24);
 
@@ -718,9 +743,19 @@ save_image (GFile             *file,
   buffer = gimp_drawable_get_buffer (drawable_ID);
 
   if (has_alpha)
-    format = babl_format ("R'G'B'A u8");
+    {
+      if (out_linear)
+        format = babl_format ("RGBA u8");
+      else
+        format = babl_format ("R'G'B'A u8");
+    }
   else
-    format = babl_format ("R'G'B' u8");
+    {
+      if (out_linear)
+        format = babl_format ("RGB u8");
+      else
+        format = babl_format ("R'G'B' u8");
+    }
 
   gegl_buffer_get (buffer,
                    GEGL_RECTANGLE (0, 0, width, height),