OpenCV Background Subtraction sample code

Dear Peter

Here is your answer.
I hope this posting & source code help to you.
And This page also is good explain to use background subtraction.
http://docs.opencv.org/master/d1/dc5/tutorial_background_subtraction.html#gsc.tab=0

This is simple code for example background subtraction.

The input is cam video.
Before get video frame, source code set some options.
MOG2, ROI, and morphology

in while, blur is option for reduce noise,
And morphology is also option.
As your project purpose and camera environment, you add more pre-processing.

But I don't add labeling code, normally do labeling processing after background subtration, because blob selecting(valid size or not), blob counting, interpretation of blob.

More information
Background subtraction code.
http://study.marearts.com/search/label/Background%20subtraction
Morphology
http://study.marearts.com/search/label/Morphology
Labeling (findContours)http://study.marearts.com/search/label/Blob%20labeling

Thank you.

#include "opencv2/opencv.hpp"

using namespace cv;

int main(int, char)
{
 VideoCapture cap(0); // open the default camera
 if (!cap.isOpened()) // check if we succeeded
  return -1;

 Ptr< BackgroundSubtractorMOG2 > MOG2 = createBackgroundSubtractorMOG2(3000, 64);
 //Options
 //MOG2->setHistory(3000);
 //MOG2->setVarThreshold(128);
 //MOG2->setDetectShadows(1); //shadow detection on/off
 Mat Mog_Mask;
 Mat Mog_Mask_morpho;

 Rect roi(100, 100, 300, 300);
 
 namedWindow("Origin", 1);
 namedWindow("ROI", 1);
 Mat frame;
 Mat RoiFrame;
 Mat BackImg;

 int LearningTime=0; //300;

 Mat element;
 element = getStructuringElement(MORPH_RECT, Size(9, 9), Point(4, 4));

 for (;;)
 {
  
  cap >> frame; // get a new frame from camera
  if (frame.empty())
   break;

  //option 
  blur(frame(roi), RoiFrame, Size(3, 3));
  //RoiFrame = frame(roi);

  //Mog processing
  MOG2->apply(RoiFrame, Mog_Mask);

  if (LearningTime < 300)
  {
   LearningTime++;
   printf("background learning %d \n", LearningTime);
  }
  else
   LearningTime = 301;

  //Background Imge get
  MOG2->getBackgroundImage(BackImg);  

  //morphology 
  morphologyEx(Mog_Mask, Mog_Mask_morpho, CV_MOP_DILATE, element);
  //Binary
  threshold(Mog_Mask_morpho, Mog_Mask_morpho, 128, 255, CV_THRESH_BINARY);  

  imshow("Origin", frame);
  imshow("ROI", RoiFrame);
  imshow("MogMask", Mog_Mask);
  imshow("BackImg", BackImg);
  imshow("Morpho", Mog_Mask_morpho);

  if (waitKey(30) >= 0)
   break;
 }

 
 return 0;
}

..

OpenCV morphologyEx, getStructuringElement function example source

This is example source code.

Mat img;
img = imread("moSample.jpg");

Mat element = getStructuringElement(MORPH_RECT, Size(3, 3), Point(1,1) );
Mat rImg;
morphologyEx(img, rImg, CV_MOP_CLOSE, element);
//morphologyEx(img, img, CV_MOP_CLOSE, element); -> It is also ok.

namedWindow("i");
imshow("i",img);
namedWindow("r");
imshow("r",rImg);
cvWaitKey(0);

In here
We can set filter box size and center point using getStructuringElement function.
-first parameter has
MORPH_RECT, MORPH_CROSS, MORPH_ELLIPSE
They show the shape of the filter box.

-second parameter means size of box.
-third parameter means center point of the box.

This picture is result of morphology processing.
using 9x9 box size /  4,4 center

Thank you.