Local adjustments - Log encoding - Ciecam16 ContrastJ - contrastQ - contrast threshold (#6169)

* Added contrast threshold Log encoding

* Improve contrast threshold

* Chanhe tooltip

* Change sign threshold when contrast negative

* Another change threshold with contrast Q and J

rtgui/locallabtools.h

@@ -1317,6 +1317,7 @@ private:
     Adjuster* const lightq;
     Adjuster* const contl;
     Adjuster* const contq;
+    Adjuster* const contthres;
     Adjuster* const colorfl;
     Adjuster* const saturl;
     MyExpander* const expL;