http://www.imagemagick.org/discourse-server/viewtopic.php?f=1&t=31928

diff --git a/MagickCore/compare.c b/MagickCore/compare.c
index 1e014cf7a246a2ae1794440387f0f1e0f2d4b475..768aa18c33a62e85427012d9c43adcfaeabd0c5c 100644 (file)
--- a/MagickCore/compare.c
+++ b/MagickCore/compare.c
@@ -2016,6 +2016,7 @@ MagickExport Image *SimilarityImage(const Image *image,const Image *reference,
       }
   }
   similarity_view=DestroyCacheView(similarity_view);
+  (void) SetImageAlphaChannel(similarity_image,OffAlphaChannel,exception);
   if (status == MagickFalse)
     similarity_image=DestroyImage(similarity_image);
   return(similarity_image);