-option "lower" l "Lower intensity (default=min)" double no
-option "upper" u "Upper intensity (default=max)" double no
-option "inside" - "Inside value" double no default="1"
-option "outside" - "Outside value" double no default="0"
+option "lower" l "Lower intensity (default=min), fg is greater than this value" double no
+option "upper" u "Upper intensity (default=max), fg is lower than this value" double no
+
+option "fg" - "Foreground (FG) or 'inside' value" double no default="1"
+option "bg" - "Background (BG) or 'ouside' value" double no default="0"
+option "mode" - "Use FG and/or BG values (if FG, the BG is replaced by the input image values)" values="FG","BG","both" default="both" required
+