Changed GUI behaviour so that the first slider sets the reference exponent (green channel), and the other two sliders set the ratio of the red/blue exponent to the reference one. This should be more intuitive, and less confusing when clicking on the reset-to-default slider button. Now the first slider sets the general contrast, while the other two affect the color.

Lowered exponent slider max value from 6 to 4 (it was too large to be useful). New sliders are log-scale.

rtgui/filmnegative.h

@@ -79,14 +79,11 @@ private:
 
     FilmNegProvider* fnp;
 
-    Adjuster* const redExp;
     Adjuster* const greenExp;
-    Adjuster* const blueExp;
+    Adjuster* const redRatio;
+    Adjuster* const blueRatio;
 
     Gtk::Grid* const spotgrid;
     Gtk::ToggleButton* const spotbutton;
     sigc::connection spotConn;
-
-    double redRatio;
-    double blueRatio;
 };