-option "lower" l "Lower intensity (default=min)" double no
-option "upper" u "Upper intensity (default=max)" double no
-option "fg" - "Foreground (FG) value" double no default="1"
-option "bg" - "Background (BG) value" double no default="0"
-option "setBG" - "No FG, keep values from input" flag off
-option "setFG" - "No BG, keep values from input" flag off
+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