diff --git a/imageviewer-qt4.cpp b/imageviewer-qt4.cpp
index 0e7b023..94bda10 100644
--- a/imageviewer-qt4.cpp
+++ b/imageviewer-qt4.cpp
@@ -73,6 +73,10 @@ void ImageViewer::initializeImage() {
   analyzeImage();
 }
 
+int ImageViewer::calcIntensity(int r, int g, int b) {
+  return (int) qRound(0.299*r + 0.587*g + 0.114*b);
+}
+
 /**
  * In case it is needed, convert the loaded image into grayscale.
  * @brief ImageViewer::convertToMonochrome
@@ -86,7 +90,7 @@ void ImageViewer::convertToMonochrome() {
         int r,g,b;
         QColor color = QColor::fromRgb(image->pixel(x, y));
         color.getRgb(&r,&g,&b);
-        int intensity = (int)(0.299*r+0.587*g+0.114*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());
@@ -206,7 +210,7 @@ void ImageViewer::analyzeImage() {
 	int r,g,b;
 	QColor color = QColor::fromRgb(image->pixel(x, y));
 	color.getRgb(&r,&g,&b);
-	int intensity = (int)(0.299*r+0.587*g+0.114*b);
+	int intensity = calcIntensity(r, g, b);
 	grayscale_absolute_histogramm[intensity] += 1;
       }
     }
@@ -250,7 +254,7 @@ int ImageViewer::getIntensityVariance() {
       QColor color = QColor::fromRgb(image->pixel(x, y));
       int r,g,b;
       color.getRgb(&r,&g,&b);
-      int intensity = (int)(0.299*r+0.587*g+0.114*b);
+      int intensity = calcIntensity(r, g, b);
       int diff = std::abs(intensity - average_intensity);
       sumDifference += diff;
     }
diff --git a/imageviewer-qt4.h b/imageviewer-qt4.h
index ce7b639..1cf60e9 100644
--- a/imageviewer-qt4.h
+++ b/imageviewer-qt4.h
@@ -41,6 +41,7 @@
 #ifndef IMAGEVIEWER_H
 #define IMAGEVIEWER_H
 
+#include <QtGlobal>
 #include <QMainWindow>
 #include <QPrinter>
 #include <QtGui>
@@ -132,6 +133,7 @@ class ImageViewer : public QMainWindow {
 
   private:
     // Custom methods
+    int calcIntensity(int r, int g, int b);
     void drawRainbowCross(int h);
     int getAverageIntensity();
     int getIntensityVariance();