diff --git a/rtengine/improccoordinator.cc b/rtengine/improccoordinator.cc
index 318f1e05e..7a43bac14 100644
--- a/rtengine/improccoordinator.cc
+++ b/rtengine/improccoordinator.cc
@@ -835,12 +835,12 @@ void ImProcCoordinator::updatePreviewImage(int todo, bool panningRelatedChange)
                 CurveFactory::complexCurvelocal(ecomp, black / 65535., hlcompr, hlcomprthresh, shcompr, br, cont, lumar,
                                                 hltonecurveloc, shtonecurveloc, tonecurveloc, lightCurveloc, avg,
                                                 sca);
-
-                if (locallListener) {
-                    locallListener->refChanged(huer, lumar, chromar);
+                if (sp == params.locallab.selspot) {
+                    if (locallListener) {
+                        locallListener->refChanged(huer, lumar, chromar);
+                    }
                 }
 
-
                 // Locallab tools computation
                 /* Notes:
                  * - shbuffer is used as nullptr
diff --git a/rtgui/curveeditor.cc b/rtgui/curveeditor.cc
index 3d1223bdf..795378d7c 100644
--- a/rtgui/curveeditor.cc
+++ b/rtgui/curveeditor.cc
@@ -247,6 +247,7 @@ CurveEditor::CurveEditor (Glib::ustring text, CurveEditorGroup* ceGroup, CurveEd
 {
 
     bgHistValid = false;
+    locallabRef = 0.0;    
     remoteDrag = false;
     selected = DCT_Linear;
     bottomBarCP = nullptr;
@@ -321,6 +322,19 @@ void CurveEditor::updateBackgroundHistogram(const LUTu& hist)
     subGroup->updateBackgroundHistogram(this);
 }
 
+/*
+ * Update Locallab reference value displayed in the background
+ */
+void CurveEditor::updateLocallabBackground(double ref)
+{
+    // Copy Locallab reference value in the curve editor cache
+    locallabRef = ref;
+
+     // Then call the curve editor group to eventually update the histogram
+    subGroup->updateLocallabBackground(this);
+}
+
+
 // Open up the curve if it has modifications and it's not already opened
 // Returns: true if curve was non linear and opened
 bool CurveEditor::openIfNonlinear()
diff --git a/rtgui/curveeditor.h b/rtgui/curveeditor.h
index 4cf49a377..64dfce9c9 100644
--- a/rtgui/curveeditor.h
+++ b/rtgui/curveeditor.h
@@ -58,7 +58,7 @@ protected:
     PopUpToggleButton* curveType;
     LUTu histogram; // histogram values
     bool bgHistValid;
-
+    double locallabRef; // Locallab reference value
     bool remoteDrag;
 
     int selected;
@@ -94,7 +94,7 @@ public:
     bool isUnChanged ();
     void setUnChanged (bool uc);
     void updateBackgroundHistogram(const LUTu& hist);
-
+    void updateLocallabBackground(double ref);
     void setLeftBarColorProvider(ColorProvider* cp, int callerId);
     void setBottomBarColorProvider(ColorProvider* cp, int callerId);
     void setCurveColorProvider(ColorProvider* cp, int callerId);
diff --git a/rtgui/curveeditorgroup.cc b/rtgui/curveeditorgroup.cc
index 4e5f038d6..2ef44a211 100644
--- a/rtgui/curveeditorgroup.cc
+++ b/rtgui/curveeditorgroup.cc
@@ -269,6 +269,7 @@ void CurveEditorGroup::curveTypeToggled(CurveEditor* ce)
 
         if (ct < ce->subGroup->valUnchanged) {
             ce->subGroup->restoreDisplayedHistogram();
+            ce->subGroup->restoreLocallabBackground();
         }
     } else {
         // The button is now released, so we have to hide this CurveEditor
diff --git a/rtgui/curveeditorgroup.h b/rtgui/curveeditorgroup.h
index 80a1a95a4..721e71d02 100644
--- a/rtgui/curveeditorgroup.h
+++ b/rtgui/curveeditorgroup.h
@@ -136,6 +136,7 @@ public:
     }
     void updateEditButton(CurveEditor* curve, Gtk::ToggleButton *button, sigc::connection &connection);
     virtual void updateBackgroundHistogram (CurveEditor* ce) {}
+    virtual void updateLocallabBackground(CurveEditor* ce) {};
     virtual void switchGUI() = 0;
     virtual void refresh(CurveEditor *curveToRefresh) = 0;
     virtual void editModeSwitchedOff() = 0;
@@ -165,6 +166,7 @@ protected:
     virtual void storeCurveValues (CurveEditor* ce, const std::vector<double>& p) = 0;
     virtual void storeDisplayedCurve () = 0;
     virtual void restoreDisplayedHistogram() {};
+    virtual void restoreLocallabBackground() {};
     virtual void removeEditor () = 0;
     virtual const std::vector<double> getCurveFromGUI (int type) = 0;
 
diff --git a/rtgui/flatcurveeditorsubgroup.cc b/rtgui/flatcurveeditorsubgroup.cc
index 376bb55c2..a6b9416d7 100644
--- a/rtgui/flatcurveeditorsubgroup.cc
+++ b/rtgui/flatcurveeditorsubgroup.cc
@@ -554,6 +554,13 @@ void FlatCurveEditorSubGroup::restoreDisplayedHistogram()
 
 }
 
+void FlatCurveEditorSubGroup::restoreLocallabBackground()
+{
+    if (parent->displayedCurve) {
+        CPointsCurve->updateLocallabBackground(parent->displayedCurve->locallabRef);
+    }
+}
+
 void FlatCurveEditorSubGroup::storeCurveValues (CurveEditor* ce, const std::vector<double>& p)
 {
     if (!p.empty()) {
@@ -627,6 +634,13 @@ bool FlatCurveEditorSubGroup::curveReset(CurveEditor *ce)
     return true;
 }
 
+void FlatCurveEditorSubGroup::updateLocallabBackground(CurveEditor* ce)
+{
+    if (ce == parent->displayedCurve) {
+        CPointsCurve->updateLocallabBackground(ce->locallabRef);
+    }
+}
+
 /*void FlatCurveEditorSubGroup::updateBackgroundHistogram (CurveEditor* ce) {
     CurveEditor* fce = (CurveEditor*)ce;
     if (fce==displayedCurve) {
diff --git a/rtgui/flatcurveeditorsubgroup.h b/rtgui/flatcurveeditorsubgroup.h
index ab2abedfb..f31ad5bbc 100644
--- a/rtgui/flatcurveeditorsubgroup.h
+++ b/rtgui/flatcurveeditorsubgroup.h
@@ -50,6 +50,7 @@ public:
 
     FlatCurveEditor* addCurve(Glib::ustring curveLabel = "", bool periodic = true);
     //virtual void updateBackgroundHistogram (CurveEditor* ce);
+    void updateLocallabBackground(CurveEditor* ce) override;    
     void switchGUI() override;
     void refresh(CurveEditor *curveToRefresh) override;
     void editModeSwitchedOff() override;
@@ -66,6 +67,7 @@ protected:
     void storeCurveValues (CurveEditor* ce, const std::vector<double>& p) override;
     void storeDisplayedCurve () override;
     void restoreDisplayedHistogram () override;
+    void restoreLocallabBackground() override;
     void savePressed ();
     void loadPressed ();
     void copyPressed ();
diff --git a/rtgui/locallab.cc b/rtgui/locallab.cc
index 5d4116683..bbc61719e 100644
--- a/rtgui/locallab.cc
+++ b/rtgui/locallab.cc
@@ -53,11 +53,11 @@ Locallab::Locallab():
     expsoft(new MyExpander(true, M("TP_LOCALLAB_SOFT"))),
     expblur(new MyExpander(true, M("TP_LOCALLAB_BLUFR"))),
     exptonemap(new MyExpander(true, M("TP_LOCALLAB_TM"))),
-    expreti(new MyExpander(true, M("TP_LOCALLAB_RETI"))),
-    expsharp(new MyExpander(true, M("TP_LOCALLAB_SHARP"))),
+    expreti(new MyExpander(true, new Gtk::HBox())),
+    expsharp(new MyExpander(true, new Gtk::HBox())),
     expcontrast(new MyExpander(true, M("TP_LOCALLAB_LOC_CONTRAST"))),
-    expcbdl(new MyExpander(true, M("TP_LOCALLAB_CBDL"))),
-    expdenoi(new MyExpander(true, M("TP_LOCALLAB_DENOIS"))),
+    expcbdl(new MyExpander(true, new Gtk::HBox())),
+    expdenoi(new MyExpander(true, new Gtk::HBox())),
 
 
     // CurveEditorGroup widgets
@@ -201,8 +201,6 @@ Locallab::Locallab():
     lumacontrastMinusButton(Gtk::manage(new Gtk::Button(M("TP_DIRPYREQUALIZER_LUMACONTRAST_MINUS")))),
     lumaneutralButton(Gtk::manage(new Gtk::Button(M("TP_DIRPYREQUALIZER_LUMANEUTRAL")))),
     lumacontrastPlusButton(Gtk::manage(new Gtk::Button(M("TP_DIRPYREQUALIZER_LUMACONTRAST_PLUS")))),
-    transLabels(Gtk::manage(new Gtk::Label("---"))),
-    transLabels2(Gtk::manage(new Gtk::Label("---"))),
     maskcolFrame(Gtk::manage(new Gtk::Frame(M("TP_LOCALLAB_SHOW")))),
     maskexpFrame(Gtk::manage(new Gtk::Frame(M("TP_LOCALLAB_SHOW")))),
     gridFrame(Gtk::manage(new Gtk::Frame(M("TP_LOCALLAB_LABGRID")))),
@@ -210,10 +208,7 @@ Locallab::Locallab():
     // Others
     defparams(nullptr),
     defpedited(nullptr),
-    pe(nullptr),
-    nexthuer(0.),
-    nextlumar(0.),
-    nextchromar(0.)
+    pe(nullptr)
 
 {
     ToolVBox* const panel = Gtk::manage(new ToolVBox());
@@ -389,8 +384,9 @@ Locallab::Locallab():
     colorBox->pack_start(*invers);
     maskcolFrame->set_label_align(0.025, 0.5);
     ToolParamBlock* const maskcolBox = Gtk::manage(new ToolParamBlock());
-    maskcolBox->pack_start(*transLabels, Gtk::PACK_SHRINK, 4);
-    maskcolBox->pack_start(*showmaskcolMethod, Gtk::PACK_SHRINK, 0);
+//    maskcolBox->pack_start(*transLabels, Gtk::PACK_SHRINK, 4);
+//    maskcolBox->pack_start(*showmaskcolMethod, Gtk::PACK_SHRINK, 0);
+    maskcolBox->pack_start(*showmaskcolMethod, Gtk::PACK_SHRINK, 4);
     maskcolBox->pack_start(*enaColorMask, Gtk::PACK_SHRINK, 0);
     maskcolBox->pack_start(*maskCurveEditorG, Gtk::PACK_SHRINK, 4); // Padding is mandatory to correct behavior of curve editor
     maskcolBox->pack_start(*blendmaskcol, Gtk::PACK_SHRINK, 0);
@@ -495,8 +491,9 @@ Locallab::Locallab():
     exposeBox->pack_start(*inversex);
     maskexpFrame->set_label_align(0.025, 0.5);
     ToolParamBlock* const maskexpBox = Gtk::manage(new ToolParamBlock());
-    maskexpBox->pack_start(*transLabels2, Gtk::PACK_SHRINK, 4);
-    maskexpBox->pack_start(*showmaskexpMethod, Gtk::PACK_SHRINK, 0);
+    maskexpBox->pack_start(*showmaskexpMethod, Gtk::PACK_SHRINK, 4);
+//    maskexpBox->pack_start(*transLabels2, Gtk::PACK_SHRINK, 4);
+//    maskexpBox->pack_start(*showmaskexpMethod, Gtk::PACK_SHRINK, 0);
     maskexpBox->pack_start(*enaExpMask, Gtk::PACK_SHRINK, 0);
     maskexpBox->pack_start(*maskexpCurveEditorG, Gtk::PACK_SHRINK, 4); // Padding is mandatory to correct behavior of curve editor
     maskexpBox->pack_start(*blendmaskexp, Gtk::PACK_SHRINK, 0);
@@ -663,9 +660,18 @@ Locallab::Locallab():
     exptonemap->add(*tmBox);
     exptonemap->setLevel(2);
 
- //   panel->pack_start(*exptonemap, false, false);
+//   panel->pack_start(*exptonemap, false, false);
 
     // Retinex
+    Gtk::HBox* const retiTitleHBox = Gtk::manage(new Gtk::HBox());
+    Gtk::Label* const retiLabel = Gtk::manage(new Gtk::Label());
+    retiLabel->set_markup(Glib::ustring("<b>") + escapeHtmlChars(M("TP_LOCALLAB_RETI")) + Glib::ustring("</b>"));
+    retiLabel->set_alignment(Gtk::ALIGN_START, Gtk::ALIGN_CENTER);
+    retiTitleHBox->pack_start(*retiLabel, Gtk::PACK_EXPAND_WIDGET, 0);
+    RTImage *retiImage = Gtk::manage (new RTImage("one-to-one-small.png"));
+    retiImage->set_tooltip_text(M("TP_GENERAL_11SCALE_TOOLTIP"));
+    retiTitleHBox->pack_end(*retiImage, Gtk::PACK_SHRINK, 0);
+    expreti->setLabel(retiTitleHBox);
     expreti->signal_button_release_event().connect_notify(sigc::bind(sigc::mem_fun(this, &Locallab::foldAllButMe), expreti));
     enableretiConn = expreti->signal_enabled_toggled().connect(sigc::bind(sigc::mem_fun(this, &Locallab::enableToggled), expreti));
 
@@ -716,6 +722,16 @@ Locallab::Locallab():
     panel->pack_start(*expreti, false, false);
 
     // Sharpening
+    Gtk::HBox* const sharpTitleHBox = Gtk::manage(new Gtk::HBox());
+    Gtk::Label* const sharpLabel = Gtk::manage(new Gtk::Label());
+    sharpLabel->set_markup(Glib::ustring("<b>") + escapeHtmlChars(M("TP_LOCALLAB_SHARP")) + Glib::ustring("</b>"));
+    sharpLabel->set_alignment(Gtk::ALIGN_START, Gtk::ALIGN_CENTER);
+    sharpTitleHBox->pack_start(*sharpLabel, Gtk::PACK_EXPAND_WIDGET, 0);
+    RTImage *sharpImage = Gtk::manage (new RTImage("one-to-one-small.png"));
+    sharpImage->set_tooltip_text(M("TP_GENERAL_11SCALE_TOOLTIP"));
+    sharpTitleHBox->pack_end(*sharpImage, Gtk::PACK_SHRINK, 0);
+    expsharp->setLabel(sharpTitleHBox);
+    
     expsharp->signal_button_release_event().connect_notify(sigc::bind(sigc::mem_fun(this, &Locallab::foldAllButMe), expsharp));
     enablesharpConn = expsharp->signal_enabled_toggled().connect(sigc::bind(sigc::mem_fun(this, &Locallab::enableToggled), expsharp));
 
@@ -776,6 +792,15 @@ Locallab::Locallab():
     panel->pack_start(*expcontrast, false, false);
 
     // Contrast by detail levels
+    Gtk::HBox* const cbdlTitleHBox = Gtk::manage(new Gtk::HBox());
+    Gtk::Label* const cbdlLabel = Gtk::manage(new Gtk::Label());
+    cbdlLabel->set_markup(Glib::ustring("<b>") + escapeHtmlChars(M("TP_LOCALLAB_CBDL")) + Glib::ustring("</b>"));
+    cbdlLabel->set_alignment(Gtk::ALIGN_START, Gtk::ALIGN_CENTER);
+    cbdlTitleHBox->pack_start(*cbdlLabel, Gtk::PACK_EXPAND_WIDGET, 0);
+    RTImage *cbdlImage = Gtk::manage (new RTImage("one-to-one-small.png"));
+    cbdlImage->set_tooltip_text(M("TP_GENERAL_11SCALE_TOOLTIP"));
+    cbdlTitleHBox->pack_end(*cbdlImage, Gtk::PACK_SHRINK, 0);
+    expcbdl->setLabel(cbdlTitleHBox);   
     expcbdl->signal_button_release_event().connect_notify(sigc::bind(sigc::mem_fun(this, &Locallab::foldAllButMe), expcbdl));
     enablecbdlConn = expcbdl->signal_enabled_toggled().connect(sigc::bind(sigc::mem_fun(this, &Locallab::enableToggled), expcbdl));
     expcbdl->set_tooltip_text(M("TP_LOCALLAB_EXPCBDL_TOOLTIP"));
@@ -827,6 +852,15 @@ Locallab::Locallab():
     panel->pack_start(*expcbdl, false, false);
 
     // Denoise
+    Gtk::HBox* const denoiTitleHBox = Gtk::manage(new Gtk::HBox());
+    Gtk::Label* const denoiLabel = Gtk::manage(new Gtk::Label());
+    denoiLabel->set_markup(Glib::ustring("<b>") + escapeHtmlChars(M("TP_LOCALLAB_DENOIS")) + Glib::ustring("</b>"));
+    denoiLabel->set_alignment(Gtk::ALIGN_START, Gtk::ALIGN_CENTER);
+    denoiTitleHBox->pack_start(*denoiLabel, Gtk::PACK_EXPAND_WIDGET, 0);
+    RTImage *denoiImage = Gtk::manage (new RTImage("one-to-one-small.png"));
+    denoiImage->set_tooltip_text(M("TP_GENERAL_11SCALE_TOOLTIP"));
+    denoiTitleHBox->pack_end(*denoiImage, Gtk::PACK_SHRINK, 0);
+    expdenoi->setLabel(denoiTitleHBox);
     expdenoi->signal_button_release_event().connect_notify(sigc::bind(sigc::mem_fun(this, &Locallab::foldAllButMe), expdenoi));
     enabledenoiConn = expdenoi->signal_enabled_toggled().connect(sigc::bind(sigc::mem_fun(this, &Locallab::enableToggled), expdenoi));
 
@@ -998,59 +1032,44 @@ void Locallab::writeOptions(std::vector<int> &tpOpen)
 
 }
 
-void Locallab::refChanged(double huer, double lumar, double chromar)
-{
-    nexthuer = huer;
-    nextlumar = lumar / 100.f;
-    nextchromar = chromar / 137.4f;
-    float h = Color::huelab_to_huehsv2(nexthuer);
-    h += 1.f / 6.f;
-
-    if (h > 1.f) {
-        h -= 1.f;
-    }
-
-    nexthuer = h;
-    //printf("nh=%f nl=%f nc=%f\n", nexthuer, nextlumar, nextchromar);
-
-
-    idle_register.add(
-    [this]() -> bool {
-        GThreadLock lock; // All GUI access from idle_add callbacks or separate thread HAVE to be protected
-        // FIXME: The above can't be true?!
-        disableListener();
-        enableListener();
-        updateLabel();
-        return false;
-    }
-    );
-
-
-}
-
-
-void Locallab::updateLabel()
+void Locallab::refChanged (double huer, double lumar, double chromar)
 {
     if (!batchMode) {
-        float nX, nY, nZ;
-
-        nY = nextlumar;
-        nX = nextchromar;
-        nZ = nexthuer;
-        {
-            transLabels->set_text(
-                Glib::ustring::compose(M("TP_LOCALLAB_REFLABEL"),
-                                       Glib::ustring::format(std::fixed, std::setprecision(3), nX),
-                                       Glib::ustring::format(std::fixed, std::setprecision(3), nY),
-                                       Glib::ustring::format(std::fixed, std::setprecision(3), nZ))
-            );
-            transLabels2->set_text(
-                Glib::ustring::compose(M("TP_LOCALLAB_REFLABEL"),
-                                       Glib::ustring::format(std::fixed, std::setprecision(3), nX),
-                                       Glib::ustring::format(std::fixed, std::setprecision(3), nY),
-                                       Glib::ustring::format(std::fixed, std::setprecision(3), nZ))
-            );
+        // Hue reference normalization (between 0 and 1)
+        double normHuer = huer;
+        float h = Color::huelab_to_huehsv2(normHuer);
+        h += 1.f/6.f;
+        if (h > 1.f) {
+            h -= 1.f;
         }
+        normHuer = h;
+
+        // Luma reference normalization (between 0 and 1)
+        double normLumar = lumar / 100.f;
+
+        // Chroma reference normalization (between 0 and 1)
+        double normChromar = chromar / 137.4f;
+
+        // printf("nh=%f nl=%f nc=%f\n", normHuer, normLumar, normChromar);
+
+        idle_register.add(
+            [this, normHuer, normLumar, normChromar]() -> bool
+            {
+                GThreadLock lock; // All GUI access from idle_add callbacks or separate thread HAVE to be protected
+
+                // Update Color & Light mask background
+                CCmaskshape->updateLocallabBackground(normChromar);
+                LLmaskshape->updateLocallabBackground(normLumar);
+                HHmaskshape->updateLocallabBackground(normHuer);
+
+                // Update Exposure mask background
+                CCmaskexpshape->updateLocallabBackground(normChromar);
+                LLmaskexpshape->updateLocallabBackground(normLumar);
+                HHmaskexpshape->updateLocallabBackground(normHuer);
+
+                return false;
+            }
+        );
     }
 }
 
@@ -1091,7 +1110,7 @@ void Locallab::lumacontrastPlusPressed()
 
     for (int i = 0; i < 5; i++) {
         float inc = (5 - i);
-        multiplier[i]->setValue(multiplier[i]->getValue() + 0.01f * inc );
+        multiplier[i]->setValue(multiplier[i]->getValue() + 0.01f * inc);
     }
 
     // Raise event (only for first multiplier because associated event concerns all multipliers)
@@ -3198,6 +3217,7 @@ void Locallab::adjusterChanged(Adjuster * a, double newval)
         }
 
     }
+
     // Vibrance
     if (a == pastels && pastSatTog->get_active() && !(multiImage && pastSatTog->get_inconsistent())) {
         saturated->setValue(newval);
diff --git a/rtgui/locallab.h b/rtgui/locallab.h
index 1b3e32bbe..79b7d7fbc 100644
--- a/rtgui/locallab.h
+++ b/rtgui/locallab.h
@@ -232,8 +232,8 @@ private:
     Gtk::Button* const lumaneutralButton;
     Gtk::Button* const lumacontrastPlusButton;
     sigc::connection lumacontrastMinusPressedConn, lumaneutralPressedConn, lumacontrastPlusPressedConn;
-    Gtk::Label* transLabels;
-    Gtk::Label* transLabels2;
+//    Gtk::Label* transLabels;
+//    Gtk::Label* transLabels2;
     Gtk::Frame* maskcolFrame;
     Gtk::Frame* maskexpFrame;
     Gtk::Frame* gridFrame;
@@ -301,9 +301,6 @@ private:
     void updateLocallabGUI(const rtengine::procparams::ProcParams* pp, const ParamsEdited* pedited, int index);
     void updateSpecificGUIState();
     void setParamEditable(bool cond);
-    double nexthuer;
-    double nextlumar;
-    double nextchromar;
 
 
 public:
@@ -323,7 +320,6 @@ public:
     void writeOptions(std::vector<int> &tpOpen);
     void updateToolState(std::vector<int> &tpOpen);
     void refChanged(double huer, double lumar, double chromar);
-    void updateLabel();
 
     // Mask visibility management functions
     struct llMaskVisibility {
diff --git a/rtgui/myflatcurve.cc b/rtgui/myflatcurve.cc
index 9b64ee516..dd2478da9 100644
--- a/rtgui/myflatcurve.cc
+++ b/rtgui/myflatcurve.cc
@@ -39,7 +39,8 @@ MyFlatCurve::MyFlatCurve () :
     deletedPointX(0.0),
     leftTanHandle({0.0, 0.0}),
     rightTanHandle({0.0, 0.0}),
-    draggingElement(false)
+    draggingElement(false),
+    locallabRef(0.0)
 {
 
     graphW = get_allocation().get_width() - RADIUS * 2;
@@ -164,6 +165,19 @@ void MyFlatCurve::draw ()
 
     Gdk::RGBA c;
 
+// Draw Locallab reference value in the background
+    if (locallabRef > 0.0) {
+        cr->set_line_width(1.0);
+        cr->move_to(double(graphX + 1), double(graphY - 1));
+        c = style->get_color(state);
+        cr->set_source_rgba(c.get_red(), c.get_green(), c.get_blue(), 0.2);
+        cr->line_to(double(graphX + 1), double(graphY - 1) -  double(graphH - 2));
+        cr->line_to(double(graphX) + 1.5 + locallabRef*double(graphW -2), double(graphY - 1) - double(graphH - 2));
+        cr->line_to(double(graphX) + 1.5 + locallabRef*double(graphW -2), double(graphY - 1));
+        cr->close_path();
+        cr->fill();
+        cr->stroke();
+    }
     cr->set_line_width (1.0);
 
     // draw f(x)=0.5 line
@@ -1872,6 +1886,35 @@ void MyFlatCurve::stopNumericalAdjustment()
     }
 }
 
+void MyFlatCurve::updateLocallabBackground(double ref)
+{
+    locallabRef = ref;
+
+     mcih->pending++;
+
+     idle_register.add(
+        [this]() -> bool
+        {
+            if (mcih->destroyed) {
+                if (mcih->pending == 1) {
+                    delete mcih;
+                } else {
+                    --mcih->pending;
+                }
+
+                 return false;
+            }
+
+             mcih->clearPixmap();
+            mcih->myCurve->queue_draw();
+
+             --mcih->pending;
+
+             return false;
+        }
+    );
+}
+
 void MyFlatCurve::setType (FlatCurveType t)
 {
 
diff --git a/rtgui/myflatcurve.h b/rtgui/myflatcurve.h
index c0223bfcf..da7d8905f 100644
--- a/rtgui/myflatcurve.h
+++ b/rtgui/myflatcurve.h
@@ -76,6 +76,8 @@ public:
 
 class MyFlatCurve : public MyCurve
 {
+private:
+    IdleRegister idle_register;
 
 protected:
     FlatCurveDescr curve;
@@ -103,6 +105,7 @@ protected:
     enum EditedHandle editedHandle;
     bool draggingElement;
     enum MouseOverAreas area;
+    double locallabRef; // Locallab reference value to display in the background
 
     void draw ();
     void movePoint(bool moveX, bool moveY, bool pipetteDrag = false);
@@ -137,6 +140,7 @@ public:
 
     void setPos(double pos, int chanIdx) override;
     void stopNumericalAdjustment() override;
+    void updateLocallabBackground(double ref);
 };
 
 #endif