Motion detection with OpenCV c++ - c++

Question

I'm trying to play with my webcam and OpenCV.
I follow this tuto : http://mateuszstankiewicz.eu/?p=189.
But the only result I have is one red border and I don't understand why. Could anyone help me to make it right and fix this ?
Here is my code :
#include "mvt_detection.h"
Mvt_detection::Mvt_detection()
{
}
Mvt_detection::~Mvt_detection()
{
}
cv::Mat Mvt_detection::start(cv::Mat frame)
{
cv::Mat back;
cv::Mat fore;
cv::BackgroundSubtractorMOG2 bg(5,3,true) ;
cv::namedWindow("Background");
std::vector<std::vector<cv::Point> > contours;
bg.operator ()(frame,fore);
bg.getBackgroundImage(back);
cv::erode(fore,fore,cv::Mat());
cv::dilate(fore,fore,cv::Mat());
cv::findContours(fore,contours,CV_RETR_EXTERNAL,CV_CHAIN_APPROX_NONE);
cv::drawContours(frame,contours,-1,cv::Scalar(0,0,255),2);
return frame;
}
Here is a screenshot of what our cam returns :
I tried on two other video from there and there and there is the same issue.
Thanks for the help :).

Answer 1

As #Lenjyco said, we fixe the problem.
#Micka had a good idea :
Firstly the BackgroundSubtractorMOG2 as to be instancied only ONCE.
We instantiate it in the constructor and play with the Hystory and Threashold:
Mvt_detection::Mvt_detection()
{
bg = new cv::BackgroundSubtractorMOG2(10, 16, false);
}
10 : the number of image the backgound look back to compare.
16 : the threshold level (blur)
This way, we are now able to detect motion.
Thank you !

Answer 2

I have used the following code which is similar to yours and it is working well. I am also taking the inputs from my webcam. In your code, i didnt find any imshow() and waitkey. Try to use them. My code is following:
#include "opencv2/core/core.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/video/background_segm.hpp"
#include "opencv2/highgui/highgui.hpp"
#include <stdio.h>
#include <iostream>
#include <vector>
using namespace std;
using namespace cv;
int main()
{
VideoCapture cap;
bool update_bg_model = true;
cap.open(0);
cv::BackgroundSubtractorMOG2 bg;//(100, 3, 0.3, 5);
bg.set ("nmixtures", 3);
std::vector < std::vector < cv::Point > >contours;
cv::namedWindow ("Frame");
cv::namedWindow ("Background");
Mat frame, fgmask, fgimg, backgroundImage;
for(;;)
{
cap >> frame;
bg.operator()(frame, fgimg);
bg.getBackgroundImage (backgroundImage);
cv::erode (fgimg, fgimg, cv::Mat ());
cv::dilate (fgimg, fgimg, cv::Mat ());
cv::findContours (fgimg, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_NONE);
cv::drawContours (frame, contours, -1, cv::Scalar (0, 0, 255), 2);
cv::imshow ("Frame", frame);
cv::imshow ("Background", backgroundImage);
char k = (char)waitKey(30);
if( k == 27 ) break;
}
return 0;
}

Answer 3

Problem fixed, putting BackgroundSubtractorMOG2 in my object's field and initialise it in constructor make him work well.