diff --git a/imageviewer-qt4.cpp b/imageviewer-qt4.cpp
index 16cf53a..1c06e92 100644
--- a/imageviewer-qt4.cpp
+++ b/imageviewer-qt4.cpp
@@ -85,6 +85,8 @@ int ImageViewer::calcIntensity(int r, int g, int b) {
 
 /**
  * In case it is needed, convert the loaded image into grayscale.
+ * This is one of the only methods modifying original_image!
+ * 
  * @brief ImageViewer::convertToMonochrome
  */
 void ImageViewer::convertToMonochrome() {
@@ -98,8 +100,8 @@ void ImageViewer::convertToMonochrome() {
         color.getRgb(&r,&g,&b);
         int intensity = calcIntensity(r, g, b);
         color = QColor::fromRgb(intensity, intensity, intensity);
-        image->setPixel(x, y, color.rgba());
-        original_image->setPixel(x, y, color.rgba());
+        image->setPixel(x, y, color.rgb());
+        original_image->setPixel(x, y, color.rgb());
       }
     }
     updateImageDisplay();
@@ -129,7 +131,7 @@ void ImageViewer::drawBlackLine() {
  */
 void ImageViewer::drawDiagonalCross() {
   if(image!=NULL) {
-    int color = QColor::fromHsl(120,255,125).rgba();
+    int color = QColor::fromHsl(120,255,125).rgb();
     int width = image->width();
     int height = image->height();
     for(int y=0; y<image->height(); y++) {
@@ -165,7 +167,7 @@ void ImageViewer::drawRainbowCross(int initialHue=0) {
     int range = line_slider->value();
     if(range > image->width()-2) range = image->width()-2;
     for(int i=0;i<std::min(image->width(),image->height());i++) {
-      int color = myColor.rgba();
+      int color = myColor.rgb();
       for(int r=0; r<range; r++) {
         image->setPixel(i+r,i,color);
         image->setPixel((image_width-i)-r,i,color);
@@ -284,7 +286,7 @@ void ImageViewer::updateHistogramm() {
   
   histogramm = new QImage(256, 100, QImage::Format_RGB32);
   histogramm->fill(QColor::fromRgb(200,200,200));
-  int black = QColor::fromRgb(0,0,0).rgba();
+  int black = QColor::fromRgb(0,0,0).rgb();
   for(int x=0; x<256; x++) {
     int k_max = (int) qRound((100*grayscale_relative_histogramm[x])/max);
     for(int y=0; y<k_max; y++) {
@@ -312,7 +314,7 @@ void ImageViewer::adjustBrightness(int b) {
       if(new_l > 255) new_l = 255;
       if(new_l < 0) new_l = 0;
       color.setHsl(h, s, new_l);
-      image->setPixel(x, y, color.rgba());
+      image->setPixel(x, y, color.rgb());
     }
   }
   updateImageDisplay();
@@ -337,7 +339,7 @@ void ImageViewer::adjustContrast(int c) {
       if(new_l > 255) new_l = 255;
       if(new_l < 0) new_l = 0;
       color.setHsl(h, s, new_l);
-      image->setPixel(x, y, color.rgba());
+      image->setPixel(x, y, color.rgb());
     }
   }
   updateImageDisplay();
@@ -345,12 +347,67 @@ void ImageViewer::adjustContrast(int c) {
   renewLogging();
 }
 
+/**
+ * Using the percentile given by the slider, do a robust automatic contrast adaption.
+ * 
+ * @brief ImageViewer::robustAutomaticContrastAdaption
+ */
+void ImageViewer::robustAutomaticContrastAdaption(void) {
+  int percentile = contrast_percentile_slider->value();
+  logFile << "Doing automatic robust contrast adaption (" << percentile << "%), hold tight... " << std::endl;
+  renewLogging();
+  
+  // Determine upper and lower "borders"
+  int lower_border = -1;
+  int upper_border = -1;
+  double limit = percentile / 100.0;
+  double cursor = 0.0;
+  for(int i=0; i<256; i++) {
+    cursor += grayscale_relative_histogramm[i];
+    if(cursor >= limit && lower_border == -1) {
+      lower_border = i-1;
+      if(lower_border < 0) lower_border = 0;
+    }
+    if(cursor >= 1-limit && upper_border == -1) {
+      upper_border = i;
+      if(upper_border > 255) upper_border = 255;
+      break;
+    }
+  }
+  
+  logFile << "lower border: " << lower_border << ", upper border: " << upper_border << "." << std::endl;
+  renewLogging();
+  
+  int h, s, l;
+  for(int x=0; x<image->width(); x++) {
+    for(int y=0; y<image->height(); y++) {
+      QColor color = QColor::fromRgb(original_image->pixel(x, y));
+      color.getHsl(&h, &s, &l);
+      
+      if(l < lower_border) { 
+	l = 0;
+      } else if(l > upper_border) {
+	l = 255;
+      } else {
+	l = qRound((l - lower_border) * (255.0/(upper_border-lower_border)));
+      }
+      
+      color.setHsl(h, s, l);
+      image->setPixel(x, y, color.rgb());
+    }
+  }
+  updateImageDisplay();
+
+  logFile << "done." << std::endl;
+  renewLogging();
+}
+
 
 /**************************************************************************************** 
 *   
 *  GUI elements related to the tasks are set up here.
 *
-*****************************************************************************************/
+**********************contrast_percentile_slider*******************************************************************/
 
 void ImageViewer::generateControlPanels() {
   // Tab for first task
@@ -426,6 +483,14 @@ void ImageViewer::generateControlPanels() {
   contrast_slider->setValue(255);
   QObject::connect(contrast_slider, SIGNAL(valueChanged(int)), this, SLOT (adjustContrast(int)));
 
+  contrast_percentile_slider = new QSlider(Qt::Horizontal);
+  contrast_percentile_slider->setMinimum(0);
+  contrast_percentile_slider->setMaximum(100);
+  contrast_percentile_slider->setValue(5);
+  
+  automatic_robust_contrast = new QPushButton("Automatic robust contrast adaption");
+  QObject::connect(automatic_robust_contrast, SIGNAL(clicked()), this, SLOT(robustAutomaticContrastAdaption()));
+  
   task_tab2->addWidget(stats);
   task_tab2->addWidget(new QLabel("Histogramm"));
   task_tab2->addWidget(histogramm_label);
@@ -434,6 +499,8 @@ void ImageViewer::generateControlPanels() {
   task_tab2->addWidget(brightness_slider);
   task_tab2->addWidget(new QLabel("Contrast"));
   task_tab2->addWidget(contrast_slider);
+  task_tab2->addWidget(contrast_percentile_slider);
+  task_tab2->addWidget(automatic_robust_contrast);
 
   tabWidget->addTab(task_tab_widget2, "Task #2");
   
diff --git a/imageviewer-qt4.h b/imageviewer-qt4.h
index 1cf60e9..dd2a069 100644
--- a/imageviewer-qt4.h
+++ b/imageviewer-qt4.h
@@ -93,6 +93,9 @@ class ImageViewer : public QMainWindow {
     QSlider* brightness_slider;
     QSlider* contrast_slider;
     
+    QSlider* contrast_percentile_slider;
+    QPushButton* automatic_robust_contrast;
+    
     // Third task tab
     QWidget* task_tab_widget3;
     QVBoxLayout* task_tab3;
@@ -114,6 +117,7 @@ class ImageViewer : public QMainWindow {
     void adjustBrightness(int b);
     void adjustContrast(int c);
     void convertToMonochrome();
+    void robustAutomaticContrastAdaption();
 
     void open();
     void print();