diff --git a/ppg.cpp b/ppg.cpp
index 9752e6a..0ba5961 100644
--- a/ppg.cpp
+++ b/ppg.cpp
@@ -3,13 +3,33 @@
 #include "opencv2/videoio.hpp"
 #include "opencv2/highgui.hpp"
 
-const int FPS = 30;
+const int FPS = 5;
 
 
 bool isDiscardData = true;
 int countDiscard = 0;
 const int DISCARD_DURATION = 10;
+const int BUFFER_DURATION = 10;
+const int I = 1;
 
+
+template <typename T>
+	cv::Mat plotGraph(std::vector<T>& vals, const double* YRange)
+	{
+	auto it = minmax_element(vals.begin(), vals.end());
+	float scale = 1./ceil(*it.second - *it.first);
+	float bias = *it.first;
+	int rows = YRange[1] - YRange[0] + 1;
+	cv::Mat image = 255*cv::Mat::ones( rows, vals.size(), CV_8UC3 );
+	image.setTo(255);
+	for (int i = 0; i < (int)vals.size()-1; i++)
+	{
+		cv::line(image, cv::Point(i, rows - 1 - (vals[i] -bias)*scale*YRange[1]), cv::Point(i+1, rows - 1 - (vals[i+1] -
+		bias)*scale*YRange[1]), cv::Scalar(255, 0, 0), 1);
+	}
+	return image;
+	}
+	
 int main() {
   cv::VideoCapture cap;
   cap.open(0);
@@ -40,11 +60,67 @@ int main() {
        }
        std::vector<cv::Rect> faceRectangles;
        faceDetector.detectMultiScale(frame, faceRectangles, 1.1, 3, 0,cv::Size(20, 20));
-       foreheadROI = faceRectangles[0];
-       foreheadROI.height *= 0.3;
-       cv::rectangle(frame, faceRectangles[0], cv::Scalar(0, 0, 255), 1, 1, 0);
-       cv::rectangle(frame, foreheadROI, cv::Scalar(0, 255, 0), 1, 1, 0);       
+       
+       if (faceRectangles.size() > 0)
+       {
+		foreheadROI = faceRectangles[0];
+		foreheadROI.height *= 0.3;
+		
+		cv::rectangle(frame, faceRectangles[0], cv::Scalar(0, 0, 255), 1, 1, 0);
+	       cv::rectangle(frame, foreheadROI, cv::Scalar(0, 255, 0), 1, 1, 0);  
+		
+		cv::Mat frame_forehead = frame(foreheadROI);
+		cv::Scalar avg_forehead = mean(frame_forehead);
+		bool isBufferFull = false;
+		int sampleIdBuffer = 0;
+		cv::Mat greenSignal(1, FPS*BUFFER_DURATION, CV_64F);
+		
+		if (!isBufferFull)
+		{
+			greenSignal.at<double>(0, sampleIdBuffer) = avg_forehead[1] ;
+			sampleIdBuffer++;
+			if (sampleIdBuffer == FPS*BUFFER_DURATION)
+			{
+			isBufferFull = true;
+			}
+		}
+		else
+		{
+			std::vector<double> greenSignalNormalized;
+			cv::Scalar mean, stddev;
+			cv::meanStdDev(greenSignal, mean, stddev);
+			for (int l_sample=0; l_sample < FPS*BUFFER_DURATION; l_sample++)
+			{
+				greenSignalNormalized.push_back((greenSignal.at<double>(0, l_sample) -
+				mean[0])/stddev[0]);
+			}
+			cv::Mat greenFFT;
+			std::vector<double> greenFFTModule;
+			cv::dft(greenSignalNormalized,greenFFT,cv::DFT_ROWS|cv::DFT_COMPLEX_OUTPUT);
+			cv::Mat planes[] = {cv::Mat::zeros(greenSignalNormalized.size(),1, CV_64F),
+			cv::Mat::zeros(greenSignalNormalized.size(),1, CV_64F)};
+			cv::split(greenFFT, planes); // planes[0] = Re(DFT(I),
+			// planes[1] = Im(DFT(I))
+			greenFFTModule.clear();
+			for (int l=0; l < planes[1].cols; l++)
+			{
+				double moduleFFT = pow(planes[1].at<double>(0,l),2) +
+				pow(planes[0].at<double>(0,l),2);
+				greenFFTModule.push_back(sqrt(moduleFFT));
+			}
+			// display green FFT
+			const double range[2] = {0.0, 150.0};
+			cv::imshow("FFT module green", plotGraph(greenFFTModule, range));
+
+		}
+
+		
+	}	    	
+	    	
+	            
        cv::imshow("Color", frame);
+      // int range[2] = {0, (int)(FPS*BUFFER_DURATION)};
+      // cv::imshow("green", plotGraph(greenSignalNormalized, range));
        if (cv::waitKey(1000.0 / FPS) >= 0)
            break;
        }