diff --git a/imageviewer-qt4.cpp b/imageviewer-qt4.cpp
index b9307ca..5076d84 100644
--- a/imageviewer-qt4.cpp
+++ b/imageviewer-qt4.cpp
@@ -458,7 +458,7 @@ void ImageViewer::succeedingHistogrammAdaption() {
     int h, s, l;
     for(int x=0; x<working_copy->getImage()->width(); x++) {
       for(int y=0; y<working_copy->getImage()->height(); y++) {
-	QColor color = QColor::fromRgb(original->getImage()->pixel(x, y));
+ 	QColor color = QColor::fromRgb(original->getImage()->pixel(x, y));
 	color.getHsl(&h, &s, &l);
         l = histogramm_map[l];
         color.setHsl(h, s, l);
@@ -472,20 +472,59 @@ void ImageViewer::succeedingHistogrammAdaption() {
   updateImageDisplay();
 }
 
-void ImageViewer::applyFilter() {
-  logFile << "Applying filter ...";
-  
+/**
+ * No special logic, avoid the borders and apply the filter.
+ * 
+ * @brief ImageViewer::applyBasicFilter
+ */
+void ImageViewer::applyBasicFilter() {
+  logFile << "Applying basic filter ...";
   int* data = filter_gui->getData();
+  int filter_size = filter_gui->getSize();
   
-  for(int i=0; i<filter_gui->getSize(); i++) {
-    for(int j=0; j<filter_gui->getSize(); j++) {
-      logFile << "@" << i << "," << j << " -> " << data[i*filter_gui->getSize() + j] << std::endl;
+  // sum up the filter weights
+  int filter_sum = 0;
+  for(int i=0; i<filter_size; i++) {
+    for(int j=0; j<filter_size; j++) {
+      int current_data = data[i*filter_size + j];
+      filter_sum += current_data;
+      //logFile << "@" << i << "," << j << " -> " << current_data << std::endl;
     }
-  }
+  }  
+  
+  int h, s, l;
+  // for each pixel
+  int filter_offset = ((filter_size+1)/2);
+  for(int x=0+filter_offset; x<working_copy->getImage()->width()-filter_offset; x++) {
+    for(int y=0+filter_offset; y<working_copy->getImage()->height()-filter_offset; y++) {
+      int intensity_sum = 0;
+      // sum up weighted intensity for each matrix entry
+      for(int fx=0; fx<filter_size; fx++) {
+	int dx = fx - (filter_size / 2);
+        for(int fy=0; fy<filter_size; fy++) {
+	  int dy = fy - (filter_size / 2);
+	  QColor color = QColor::fromRgb(original->getImage()->pixel(x+dx, y+dy));
+	  color.getHsl(&h, &s, &l);
+	  //std::cout << "[" << fx << "," << fy <<"] " << l << " * " << data[fx*filter_size + fy] << " = ";
+	  intensity_sum += (l * data[fx*filter_size + fy]);
+	  //std::cout << intensity_sum << std::endl;
+        }	
+      }
+      QColor color = QColor::fromRgb(original->getImage()->pixel(x, y));
+      color.getHsl(&h, &s, &l);
+      //std::cout << "old lightness: " << l << ", filter_sum: " << filter_sum << ", intensity_sum:" << intensity_sum;
+      // divide by sum of weights
+      l = qRound((intensity_sum*1.0) / filter_sum);
+      //std::cout << " --> new l: " << l << std::endl;
+      color.setHsl(h, s, l);
+      // and set it.
+      working_copy->getImage()->setPixel(x, y, color.rgb());
+    }
+  }  
   
   logFile << "done." << std::endl;
   renewLogging();
-  //updateImageDisplay();
+  updateImageDisplay();
 }
 
 
@@ -716,7 +755,7 @@ void ImageViewer::generateControlPanels() {
   filter_gui = new FilterGui();
   
   apply_filter = new QPushButton("Apply filter");
-  QObject::connect(apply_filter, SIGNAL(clicked()), this, SLOT(applyFilter()));
+  QObject::connect(apply_filter, SIGNAL(clicked()), this, SLOT(applyBasicFilter()));
 
   task_tab4_scrolllayout->addWidget(filter_size_slider);
   task_tab4_scrolllayout->addWidget(filter_gui->getWidget());
diff --git a/imageviewer-qt4.h b/imageviewer-qt4.h
index a524d87..30d13a6 100644
--- a/imageviewer-qt4.h
+++ b/imageviewer-qt4.h
@@ -157,7 +157,7 @@ class ImageViewer : public QMainWindow {
     void partialLinearHistogrammAdaption();
     void succeedingHistogrammAdaption();
     void changeFilterSize(int s);
-    void applyFilter();
+    void applyBasicFilter();
 
     void open();
     void openReference();