diff --git a/MagickCore/effect.c b/MagickCore/effect.c
index fbf159e..4e80952 100644
--- a/MagickCore/effect.c
+++ b/MagickCore/effect.c
@@ -2718,6 +2718,7 @@
     sigma+=0.25;
     if (preview_image == (Image *) NULL)
       break;
+    preview_image->alpha_trait=UndefinedPixelTrait;
     (void) DeleteImageProperty(preview_image,"label");
     (void) SetImageProperty(preview_image,"label",label,exception);
     AppendImageToList(&images,preview_image);