https://github.com/ImageMagick/ImageMagick/issues/1724

diff --git a/MagickCore/channel.c b/MagickCore/channel.c
index b7e11175e3cac1e8b30ec5797cdd91d53a215417..0189d485fc0edefa2f933f06ce3f90b81edb0de3 100644 (file)
--- a/MagickCore/channel.c
+++ b/MagickCore/channel.c
@@ -1284,6 +1284,7 @@ MagickExport MagickBooleanType SetImageAlphaChannel(Image *image,
 
         if (status == MagickFalse)
           continue;
+        ConformPixelInfo(image,&image->background_color,&background,exception);
         q=GetCacheViewAuthenticPixels(image_view,0,y,image->columns,1,
           exception);
         if (q == (Quantum *) NULL)
@@ -1291,7 +1292,6 @@ MagickExport MagickBooleanType SetImageAlphaChannel(Image *image,
             status=MagickFalse;
             continue;
           }
-        ConformPixelInfo(image,&image->background_color,&background,exception);
         background.alpha_trait=BlendPixelTrait;
         for (x=0; x < (ssize_t) image->columns; x++)
         {