diff --git a/imageviewer-qt4.cpp b/imageviewer-qt4.cpp
index 7990bde..007f6ce 100644
--- a/imageviewer-qt4.cpp
+++ b/imageviewer-qt4.cpp
@@ -724,11 +724,44 @@ void ImageViewer::runCannyEdgeThirdStep(void) {
 void ImageViewer::doUnsharpMasking(void) {
   double alpha = usm_sharpening->value();
   int gauss_width = usm_gauss_width->value();
-  logFile << "Doing USM using gauss width of " << gauss_width << " and alpha of " << alpha << std::endl;
+  double sigma = usm_gauss_sigma->value();  
+  logFile << "Doing USM using gauss width of " << gauss_width << ", sigma of " << sigma << ", and alpha of " << alpha << std::endl;
   renewLogging();
-  
-  
-  
+  int pixels = original->width() * original->height();
+  int* blurred_intensity = (int*) malloc(sizeof(int) * pixels);
+  int* mask = (int*) malloc(sizeof(int) * pixels);
+  double sum_weights = 0.0;
+  double* filter = canny_edge_machine->generateGaussFilter(gauss_width, sigma, sum_weights);
+  int h, s, l;
+  for(int x=0; x<original->width(); x++) {
+    for(int y=0; y<original->height(); y++) {
+      // Step 1: Blur the image and store seperately
+      double sum_intensity = 0.0;
+      for(int fx=0; fx<gauss_width; fx++) {
+	int dx = fx - (gauss_width/2);
+        for(int fy=0; fy<gauss_width; fy++) {
+	  int dy = fy - (gauss_width/2);
+	  QColor color = QColor::fromRgb(original->getPixel(x+dx, y+dy, LazyImage::CONSTANT));
+	  color.getHsl(&h, &s, &l);
+          sum_intensity += l;
+        }
+      }
+      double average_intensity = sum_intensity / sum_weights;
+      // Step 2: Subtract blurred image from original -> store as mask
+      QColor color = QColor::fromRgb(original->getPixel(x, y, LazyImage::CONSTANT));
+      color.getHsl(&h, &s, &l);
+      double intensity_mask = l - average_intensity;
+      // Step 3: Add weighted mask to original -> sharpening occurs.
+      double intensity_result = alpha * intensity_mask + l;
+      if(intensity_result > 255) intensity_result = 255;
+      if(intensity_result < 0) intensity_result = 0;      
+      color.setHsl(h, s, qRound(intensity_result));
+      working_copy->getImage()->setPixel(x, y, color.rgb());
+    }
+  }
+  free(filter);
+  free(mask);
+  free(blurred_intensity);
   updateImageDisplay();
 }
 /**************************************************************************************** 
@@ -1026,8 +1059,12 @@ void ImageViewer::generateControlPanels() {
   usm_sharpening->setValue(1.0);
 
   usm_gauss_width = new QDoubleSpinBox();
-  usm_gauss_width->setDecimals(5);
+  usm_gauss_width->setDecimals(0);
   usm_gauss_width->setValue(3);
+
+  usm_gauss_sigma = new QDoubleSpinBox();
+  usm_gauss_sigma->setDecimals(5);
+  usm_gauss_sigma->setValue(4);
   
   run_usm = new QPushButton("Apply unsharp masking!");
   QObject::connect(run_usm, SIGNAL(clicked()), this, SLOT(doUnsharpMasking()));
@@ -1047,8 +1084,9 @@ void ImageViewer::generateControlPanels() {
   task_tab5_scrolllayout->addWidget(new QLabel(" --- Unsharp masking --- "));
   task_tab5_scrolllayout->addWidget(new QLabel("Sharpening factor alpha"));
   task_tab5_scrolllayout->addWidget(usm_sharpening);
-  task_tab5_scrolllayout->addWidget(new QLabel("Gauss filter width sigma"));
+  task_tab5_scrolllayout->addWidget(new QLabel("Gauss filter width and sigma"));
   task_tab5_scrolllayout->addWidget(usm_gauss_width);
+  task_tab5_scrolllayout->addWidget(usm_gauss_sigma);
   task_tab5_scrolllayout->addWidget(run_usm);
   
   tabWidget->addTab(task_tab5_widget, "Task #5");
diff --git a/imageviewer-qt4.h b/imageviewer-qt4.h
index 0ac5226..25c151f 100644
--- a/imageviewer-qt4.h
+++ b/imageviewer-qt4.h
@@ -156,8 +156,9 @@ class ImageViewer : public QMainWindow {
     QPushButton* run_canny_edge_second_step;
     QPushButton* run_canny_edge_third_step;
     QPushButton* run_usm;
-    QDoubleSpinBox* usm_sharpening;    
+    QDoubleSpinBox* usm_sharpening;
     QDoubleSpinBox* usm_gauss_width;
+    QDoubleSpinBox* usm_gauss_sigma;
     
     // "My" space for storing data/results
     LazyImage* original;