diff --git a/plotter.cpp b/plotter.cpp
index abfb59f..f5c4629 100644
--- a/plotter.cpp
+++ b/plotter.cpp
@@ -550,7 +550,7 @@ void CPlotter::DrawOverlay()                   //DrawOverlay()
           filterPainter.drawLine(filterStart, 30, filterStart, m_h);
           filterPainter.drawLine(filterEnd, 30, filterEnd, m_h);
 
-          QColor blackMask(0, 0, 0, 128);
+          QColor blackMask(0, 0, 0, std::max(0, std::min(m_filterOpacity, 255)));
           filterPainter.fillRect(0, 30, filterStart, m_h, blackMask);
           filterPainter.fillRect(filterEnd+1, 30, m_Size.width(), m_h, blackMask);
       }
@@ -836,6 +836,12 @@ void CPlotter::setFilterEnabled(bool enabled){
   update();
 }
 
+void CPlotter::setFilterOpacity(int alpha){
+    m_filterOpacity=alpha;
+    DrawOverlay();
+    update();
+}
+
 void CPlotter::setFlatten(bool b1, bool b2)
 {
   m_Flatten=0;
diff --git a/plotter.h b/plotter.h
index 1988e0f..54e6d74 100644
--- a/plotter.h
+++ b/plotter.h
@@ -85,6 +85,7 @@ public:
   void setFilterCenter(int center);
   void setFilterWidth(int width);
   void setFilterEnabled(bool enabled);
+  void setFilterOpacity(int alpha);
 #if JS8_USE_REFSPEC
   void setReference(bool b) {m_bReference = b;}
   bool Reference() const {return m_bReference;}
@@ -173,6 +174,7 @@ private:
 
   float   m_sum[2048];
 
+  qint32  m_filterOpacity;
   qint32  m_dBStepSize;
   qint32  m_FreqUnits;
   qint32  m_hdivs;
diff --git a/widegraph.cpp b/widegraph.cpp
index 18e850e..1468896 100644
--- a/widegraph.cpp
+++ b/widegraph.cpp
@@ -161,6 +161,7 @@ WideGraph::WideGraph(QSettings * settings, QWidget *parent) :
     }
 
     setFilter(m_settings->value("FilterMinimum", 500).toInt(), m_settings->value("FilterMaximum", 2500).toInt());
+    setFilterOpacityPercent(m_settings->value("FilterOpacityPercent", 50).toInt());
     setFilterEnabled(m_settings->value("FilterEnabled", false).toBool());
   }
 
@@ -213,14 +214,15 @@ void WideGraph::saveSettings()                                           //saveS
   m_settings->setValue ("StartFreq", ui->widePlot->startFreq ());
   m_settings->setValue ("WaterfallPalette", m_waterfallPalette);
   m_settings->setValue ("UserPalette", QVariant::fromValue (m_userPalette.colours ()));
-  m_settings->setValue("Flatten",m_bFlatten);
-  m_settings->setValue("UseRef",m_bRef);
+  m_settings->setValue ("Flatten",m_bFlatten);
+  m_settings->setValue ("UseRef",m_bRef);
   m_settings->setValue ("HideControls", ui->controls_widget->isHidden ());
   m_settings->setValue ("FminPerBand", m_fMinPerBand);
   m_settings->setValue ("CenterOffset", ui->centerSpinBox->value());
   m_settings->setValue ("FilterMinimum", m_filterMinimum);
   m_settings->setValue ("FilterMaximum", m_filterMaximum);
   m_settings->setValue ("FilterEnabled", m_filterEnabled);
+  m_settings->setValue ("FilterOpacityPercent", ui->filterOpacitySpinBox->value());
   m_settings->setValue ("SplitState", ui->splitter->saveState());
 }
 
@@ -447,6 +449,18 @@ void WideGraph::setFilterEnabled(bool enabled){
     ui->widePlot->setFilterEnabled(enabled);
 }
 
+void WideGraph::setFilterOpacityPercent(int n){
+    // update the spinbox
+    bool blocked = ui->filterOpacitySpinBox->blockSignals(true);
+    {
+        ui->filterOpacitySpinBox->setValue(n);
+    }
+    ui->filterOpacitySpinBox->blockSignals(blocked);
+
+    // update the wide plot
+    ui->widePlot->setFilterOpacity(int((float(n)/100.0)*255));
+}
+
 int WideGraph::fSpan()
 {
   return ui->widePlot->fSpan ();
@@ -712,6 +726,10 @@ void WideGraph::on_filterCheckBox_toggled(bool b){
     setFilterEnabled(b);
 }
 
+void WideGraph::on_filterOpacitySpinBox_valueChanged(int n){
+    setFilterOpacityPercent(n);
+}
+
 void WideGraph::setRedFile(QString fRed)
 {
   ui->widePlot->setRedFile(fRed);
diff --git a/widegraph.h b/widegraph.h
index bdb7461..a300d93 100644
--- a/widegraph.h
+++ b/widegraph.h
@@ -39,6 +39,7 @@ public:
   void   setFilter(int a, int b);
   void   setFilterMinimumBandwidth(int width);
   void   setFilterEnabled(bool enabled);
+  void   setFilterOpacityPercent(int n);
   int    fSpan();
   void   saveSettings();
   void   setFsample(int n);
@@ -99,6 +100,7 @@ private slots:
   void on_filterMinSpinBox_valueChanged(int n);
   void on_filterMaxSpinBox_valueChanged(int n);
   void on_filterCheckBox_toggled(bool b);
+  void on_filterOpacitySpinBox_valueChanged(int n);
 
   void on_driftSpinBox_valueChanged(int n);
   void on_driftSyncButton_clicked();
diff --git a/widegraph.ui b/widegraph.ui
index 0c958bf..3c05d09 100644
--- a/widegraph.ui
+++ b/widegraph.ui
@@ -373,9 +373,9 @@
               <property name="geometry">
                <rect>
                 <x>0</x>
-                <y>0</y>
+                <y>-517</y>
                 <width>267</width>
-                <height>615</height>
+                <height>691</height>
                </rect>
               </property>
               <layout class="QVBoxLayout" name="verticalLayout_5">
@@ -807,6 +807,38 @@
                  </layout>
                 </widget>
                </item>
+               <item>
+                <widget class="QGroupBox" name="groupBox_9">
+                 <property name="title">
+                  <string>Filter</string>
+                 </property>
+                 <layout class="QFormLayout" name="formLayout_3">
+                  <item row="0" column="0">
+                   <widget class="QLabel" name="label_6">
+                    <property name="text">
+                     <string>Opacity:</string>
+                    </property>
+                   </widget>
+                  </item>
+                  <item row="0" column="1">
+                   <widget class="QSpinBox" name="filterOpacitySpinBox">
+                    <property name="alignment">
+                     <set>Qt::AlignCenter</set>
+                    </property>
+                    <property name="suffix">
+                     <string>%</string>
+                    </property>
+                    <property name="maximum">
+                     <number>100</number>
+                    </property>
+                    <property name="value">
+                     <number>50</number>
+                    </property>
+                   </widget>
+                  </item>
+                 </layout>
+                </widget>
+               </item>
                <item>
                 <spacer name="verticalSpacer_2">
                  <property name="orientation">