diff --git a/src/Parser/Command/SelectBitImageModeCmd.php b/src/Parser/Command/SelectBitImageModeCmd.php
index 5865029..4ead8fc 100644
--- a/src/Parser/Command/SelectBitImageModeCmd.php
+++ b/src/Parser/Command/SelectBitImageModeCmd.php
@@ -71,6 +71,7 @@ public function asPbm()
         $im -> readImageBlob($pbmBlob, 'pbm');
         $im -> rotateImage('#fff', 90.0);
         $im -> flopImage();
+        $im -> negateImage(true);
         return $im -> getImageBlob();
     }