diff --git a/imageviewer-qt4.cpp b/imageviewer-qt4.cpp
index 94bda10..4fc8c19 100644
--- a/imageviewer-qt4.cpp
+++ b/imageviewer-qt4.cpp
@@ -73,6 +73,12 @@ void ImageViewer::initializeImage() {
   analyzeImage();
 }
 
+/**
+ * Uses simple weights to calculate intensity of a pixel.
+ * Using qRound() to reduce the error of the int cast.
+ * 
+ * @brief ImageViewer::calcIntensity
+ */
 int ImageViewer::calcIntensity(int r, int g, int b) {
   return (int) qRound(0.299*r + 0.587*g + 0.114*b);
 }