diff --git a/rtgui/filmnegative.cc b/rtgui/filmnegative.cc
index 0e6ec9e8f..4956968e3 100644
--- a/rtgui/filmnegative.cc
+++ b/rtgui/filmnegative.cc
@@ -52,9 +52,9 @@ FilmNegative::FilmNegative() :
     evFilmNegativeExponents(ProcEventMapper::getInstance()->newEvent(FIRST, "HISTORY_MSG_FILMNEGATIVE_EXPONENTS")),
     evFilmNegativeEnabled(ProcEventMapper::getInstance()->newEvent(FIRST, "HISTORY_MSG_FILMNEGATIVE_ENABLED")),
     fnp(nullptr),
-    greenExp(createExponentAdjuster(this, M("TP_FILMNEGATIVE_GREEN"), 0.3, 4, 1.5)),
-    redRatio(createExponentAdjuster(this, M("TP_FILMNEGATIVE_RED"), 0.3, 3, 1.36)),
-    blueRatio(createExponentAdjuster(this, M("TP_FILMNEGATIVE_BLUE"), 0.3, 3, 0.86)),
+    greenExp(createExponentAdjuster(this, M("TP_FILMNEGATIVE_GREEN"), 0.3, 4, 1.5)),  // master exponent (green channel)
+    redRatio(createExponentAdjuster(this, M("TP_FILMNEGATIVE_RED"), 0.3, 3, (2.04 / 1.5))), // ratio of red exponent to master exponent
+    blueRatio(createExponentAdjuster(this, M("TP_FILMNEGATIVE_BLUE"), 0.3, 3, (1.29 / 1.5))), // ratio of blue exponent to master exponent
     spotgrid(Gtk::manage(new Gtk::Grid())),
     spotbutton(Gtk::manage(new Gtk::ToggleButton(M("TP_FILMNEGATIVE_PICK"))))
 {