diff --git a/src/MainWindow.cpp b/src/MainWindow.cpp
index 2d8b0dde..0f516ef0 100644
--- a/src/MainWindow.cpp
+++ b/src/MainWindow.cpp
@@ -353,31 +353,38 @@ void MainWindow::update(const cv::Mat & image)
 		delete detector;
 		ui_->label_timeDetection->setText(QString::number(time.restart()));
 
-		// EXTRACT DESCRIPTORS
 		cv::Mat descriptors;
-		cv::DescriptorExtractor * extractor = Settings::createDescriptorsExtractor();
-		extractor->compute(img, keypoints, descriptors);
-		delete extractor;
-		if((int)keypoints.size() != descriptors.rows)
+		if(keypoints.size())
 		{
-			printf("ERROR : kpt=%d != descriptors=%d\n", (int)keypoints.size(), descriptors.rows);
+			// EXTRACT DESCRIPTORS
+			cv::DescriptorExtractor * extractor = Settings::createDescriptorsExtractor();
+			extractor->compute(img, keypoints, descriptors);
+			delete extractor;
+			if((int)keypoints.size() != descriptors.rows)
+			{
+				printf("ERROR : kpt=%d != descriptors=%d\n", (int)keypoints.size(), descriptors.rows);
+			}
+			if(imageGrayScale)
+			{
+				cvReleaseImage(&imageGrayScale);
+			}
+			ui_->label_timeExtraction->setText(QString::number(time.restart()));
 		}
-		if(imageGrayScale)
+		else
 		{
-			cvReleaseImage(&imageGrayScale);
+			printf("WARNING: no features detected !?!\n");
+			ui_->label_timeExtraction->setText(QString::number(0));
 		}
-		ui_->label_timeExtraction->setText(QString::number(time.restart()));
 
 		// COMPARE
-		int alpha = 20*255/100;
-		if(!dataTree_.empty() && (Settings::getNearestNeighbor_nndrRatioUsed() || Settings::getNearestNeighbor_minDistanceUsed()))
+		if(!dataTree_.empty() && keypoints.size() && (Settings::getNearestNeighbor_nndrRatioUsed() || Settings::getNearestNeighbor_minDistanceUsed()))
 		{
 			// CREATE INDEX
 			cv::Mat environment(descriptors.rows, descriptors.cols, CV_32F);
 			descriptors.convertTo(environment, CV_32F);
 			cv::flann::Index treeFlannIndex(environment, cv::flann::KDTreeIndexParams());
 			ui_->label_timeIndexing->setText(QString::number(time.restart()));
-
+			
 			// DO NEAREST NEIGHBOR
 			int k = 1;
 			if(Settings::getNearestNeighbor_nndrRatioUsed())
@@ -390,7 +397,6 @@ void MainWindow::update(const cv::Mat & image)
 			treeFlannIndex.knnSearch(dataTree_, results, dists, k, cv::flann::SearchParams(emax) ); // maximum number of leafs checked
 			ui_->label_timeMatching->setText(QString::number(time.restart()));
 
-
 			// PROCESS RESULTS
 			if(this->isVisible())
 			{
@@ -406,7 +412,6 @@ void MainWindow::update(const cv::Mat & image)
 			for(int i=0; i<dataTree_.rows; ++i)
 			{
 				QColor color((Qt::GlobalColor)(j % 12 + 7 ));
-				color.setAlpha(alpha);
 				bool matched = false;
 				// Check if this descriptor matches with those of the objects
 				if(Settings::getNearestNeighbor_nndrRatioUsed() &&
@@ -497,7 +502,7 @@ void MainWindow::update(const cv::Mat & image)
 										}
 										else
 										{
-											objects_.at(j)->setKptColor(indexes_1.at(k), QColor(0,0,0,alpha));
+											objects_.at(j)->setKptColor(indexes_1.at(k), QColor(0,0,0));
 										}
 									}
 								}
diff --git a/src/ObjWidget.cpp b/src/ObjWidget.cpp
index df737740..6404af97 100644
--- a/src/ObjWidget.cpp
+++ b/src/ObjWidget.cpp
@@ -20,6 +20,7 @@
 #include <QtGui/QVBoxLayout>
 #include <QtGui/QGraphicsRectItem>
 #include <QtGui/QInputDialog>
+#include <QtGui/QPen>
 
 #include <QtCore/QDir>
 
@@ -201,6 +202,14 @@ void ObjWidget::setAlpha(int alpha)
 				color.setAlpha(alpha_);
 				keypointItems_.at(i)->setColor(color);
 			}
+			for(int i=0; i<rectItems_.size(); ++i)
+			{
+				QPen pen = rectItems_.at(i)->pen();
+				QColor color = pen.color();
+				color.setAlpha(alpha_);
+				pen.setColor(color);
+				rectItems_.at(i)->setPen(pen);
+			}
 		}
 		if(!_graphicsViewMode->isChecked())
 		{
@@ -282,6 +291,11 @@ void ObjWidget::addRect(QGraphicsRectItem * rect)
 		graphicsView_->scene()->addItem(rect);
 	}
 	rect->setZValue(2);
+	QPen pen = rect->pen();
+	QColor color = pen.color();
+	color.setAlpha(alpha_);
+	pen.setColor(color);
+	rect->setPen(pen);
 	rectItems_.append(rect);
 }