https://imagemagick.org/discourse-server/viewtopic.php?f=2&t=34362

diff --git a/MagickCore/image.c b/MagickCore/image.c
index ff49078e2e8ecfcd48a20eaf98d9a8a051aef413..65e865af55d2cca3908dd1af52917771f1b9152d 100644 (file)
--- a/MagickCore/image.c
+++ b/MagickCore/image.c
@@ -1750,7 +1750,7 @@ MagickExport size_t InterpretImageFilename(const ImageInfo *image_info,
         *q='\0';
         (void) CopyMagickString(filename+(p-format-offset),option,(size_t)
           (MagickPathExtent-(p-format-offset)));
-        offset+=strlen(pattern)-4;
+        offset+=strlen(pattern)-strlen(option)+3;
         *q=c;
         (void) ConcatenateMagickString(filename,r+1,MagickPathExtent);
         canonical=MagickTrue;