diff --git a/imageviewer-qt4.cpp b/imageviewer-qt4.cpp
index 6e6676e..e0906cc 100644
--- a/imageviewer-qt4.cpp
+++ b/imageviewer-qt4.cpp
@@ -235,11 +235,16 @@ void ImageViewer::adjustBrightness(int b) {
   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));
-      color.getHsl(&h, &s, &old_l);
-      new_l = old_l + delta;
-      if(new_l > 255) new_l = 255;
-      if(new_l < 0) new_l = 0;
-      color.setHsl(h, s, new_l);
+//      color.getHsl(&h, &s, &old_l);
+//      new_l = old_l + delta;
+//      if(new_l > 255) new_l = 255;
+//      if(new_l < 0) new_l = 0;
+//      color.setHsl(h, s, new_l);
+      struct yuv yuv = LazyImage::RGBToYUV(color.rgb());
+      yuv.y = yuv.y + (delta / 255.0);
+      if(yuv.y > 1) yuv.y = 1;
+      if(yuv.y < 0) yuv.y = 0;
+      color = LazyImage::YUVToRGB(yuv);
       working_copy->getImage()->setPixel(x, y, color.rgb());
     }
   }
@@ -564,7 +569,7 @@ void ImageViewer::applyBasicFilter() {
  */
 void ImageViewer::applyBasicFilterWithOverflowHandling() {
   QString chosen_mode = filter_mode_combobox->currentText();
-  LazyImage::overflowMode overflow_mode; 
+  LazyImage::overflowMode overflow_mode = LazyImage::CONSTANT; // default for compiler
   if(chosen_mode == "Zero padding") overflow_mode = LazyImage::ZERO_PADDING;
   else if(chosen_mode == "Constant") overflow_mode = LazyImage::CONSTANT;
   else if(chosen_mode == "Continuous") overflow_mode = LazyImage::CONTINUOUS;
diff --git a/lazy_image.cpp b/lazy_image.cpp
index b650411..432c163 100644
--- a/lazy_image.cpp
+++ b/lazy_image.cpp
@@ -9,6 +9,13 @@
 
 #include <math.h>
 
+struct yuv {
+  // values in [0,1]
+  double y; // brightness
+  double u; // red/green part
+  double v; // green/blue part
+};
+
 class LazyImage {
   
   private:
@@ -255,6 +262,48 @@ class LazyImage {
 	return this->img->pixel(x, y);
       }
     };
+    
+    static struct yuv RGBToYUV(QColor input) {
+      struct yuv result;
+      int input_r, input_g, input_b;
+      input.getRgb(&input_r, &input_g, &input_b);
+      //std::cout << input_r << "," << input_g << "," << input_b << " (rgb) -> (yuv) ";
+      // normalize input rgb to values in [0,1]
+      double r, g, b;
+      r = input_r / 255.0;
+      g = input_g / 255.0;
+      b = input_b / 255.0;
+      // calculate yuv
+      result.y = 0.299 * r + 0.587 * g + 0.114 * b;
+      result.u = (b - result.y) * 0.493;
+      result.v = (r - result.y) * 0.877;
+      //std::cout << result.y << "," << result.u << "," << result.v << std::endl;
+      return result;
+    };
+    
+    static QColor YUVToRGB(struct yuv input) {
+      double r, g, b;
+      // calculate rgb
+      //std::cout << input.y << "," << input.u << "," << input.v << " (yuv) -> (rgb) ";
+      b = (input.u / 0.493) + input.y;
+      r = (input.v / 0.877) + input.y;
+      // möp g = (input.y - 0.299*r - 0.144*b) / 0.587;
+      g = (1.0/0.587)*input.y - (0.299/0.587)*r - (0.114/0.585)*b;
+      // normalize into [0,255]
+      int output_r, output_g, output_b;
+      output_r = qRound(r * 255.0);
+      output_g = qRound(g * 255.0);
+      output_b = qRound(b * 255.0);
+      if(output_r < 0) output_r = 0;
+      if(output_g < 0) output_g = 0;
+      if(output_b < 0) output_b = 0;
+      if(output_r > 255) output_r = 255;
+      if(output_g > 255) output_g = 255;
+      if(output_b > 255) output_b = 255;
+      //std::cout << output_r << "," << output_g << "," << output_b << std::endl << std::endl;
+      QColor result = QColor(output_r, output_g, output_b);
+      return result;
+    };    
 
 };