(opencv) merge contours together

Question

I am doing a real time motion detection program. I find that there are a lot of contour made in my different image after i used background subtraction method . i would like to ask is there any method that can merge these contour together or make a larger rect contain all the contours?

the case now i have been done
http://singhgaganpreet.files.wordpress.com/2012/07/motioncolour.jpg
My code is here

#include <iostream>
#include <OpenCV/cv.h>
#include <OPenCV/highgui.h>

using namespace cv;
using namespace std;

CvRect rect;
CvSeq* contours = 0;
CvMemStorage* storage = NULL;
CvCapture *cam;
IplImage *currentFrame, *currentFrame_grey, *differenceImg, *oldFrame_grey;

bool first = true;

int main(int argc, char* argv[])
{
   //Create a new movie capture object.
   cam = cvCaptureFromCAM(0);

   //create storage for contours
   storage = cvCreateMemStorage(0);

   //capture current frame from webcam
   currentFrame = cvQueryFrame(cam);

   //Size of the image.
   CvSize imgSize;
   imgSize.width = currentFrame->width;
   imgSize.height = currentFrame->height;

   //Images to use in the program.
   currentFrame_grey = cvCreateImage( imgSize, IPL_DEPTH_8U, 1);                           

   while(1)
   {
          currentFrame = cvQueryFrame( cam );
          if( !currentFrame ) break;

          //Convert the image to grayscale.
          cvCvtColor(currentFrame,currentFrame_grey,CV_RGB2GRAY);

          if(first) //Capturing Background for the first time
          {
                 differenceImg = cvCloneImage(currentFrame_grey);
                 oldFrame_grey = cvCloneImage(currentFrame_grey);
                 cvConvertScale(currentFrame_grey, oldFrame_grey, 1.0, 0.0);
                 first = false;
                 continue;
          }

          //Minus the current frame from the moving average.
          cvAbsDiff(oldFrame_grey,currentFrame_grey,differenceImg);

          //bluring the differnece image
          cvSmooth(differenceImg, differenceImg, CV_BLUR);             

          //apply threshold to discard small unwanted movements
          cvThreshold(differenceImg, differenceImg, 25, 255, CV_THRESH_BINARY);

          //find contours
          cvFindContours( differenceImg, storage, &contours );

          //draw bounding box around each contour
          for(; contours!=0; contours = contours->h_next)
          {
                 rect = cvBoundingRect(contours, 0); //extract bounding box for current contour

                 //drawing rectangle
                 cvRectangle(currentFrame,                  
                              cvPoint(rect.x, rect.y),    
                              cvPoint(rect.x+rect.width, rect.y+rect.height),
                              cvScalar(0, 0, 255, 0),
                              2, 8, 0);                 
          }

          //display colour image with bounding box
          cvShowImage("Output Image", currentFrame);

          //display threshold image
          cvShowImage("Difference image", differenceImg);

          //New Background
          cvConvertScale(currentFrame_grey, oldFrame_grey, 1.0, 0.0);

          //clear memory and contours
          cvClearMemStorage( storage );
          contours = 0;

          //press Esc to exit
          char c = cvWaitKey(33);
          if( c == 27 ) break;

   }

   // Destroy the image & movies objects
   cvReleaseImage(&oldFrame_grey);
   cvReleaseImage(&differenceImg);
   cvReleaseImage(&currentFrame);
   cvReleaseImage(&currentFrame_grey);
   //cvReleaseCapture(&cam);

   return 0;

}

Answer 1

Did you try this?

std::vector<cv::Point> points;
points.insert(points.end(), contour1.begin(), contour1.end());
points.insert(points.end(), contour2.begin(), contour2.end());
convexHull(cv::Mat(points), contour);

PS. For some applications, it may be better to use approxPoly() rather than convexHull(). Just try both.

PPS. Try smoothing the resulting contour with gaussian. It also can be helpful.

Answer 2

I came across a similar problem. In my case I created an empty sequence then I filled it with the points of each contour, after that I fitted a bounding ellipse with that sequence. Here is my code segment...

CvMemStorage *storage = cvCreateMemStorage ();
CvMemStorage *storage1 = cvCreateMemStorage ();
CvSeq *contours = 0;

//find contour in BInv
cvFindContours (BInv, storage, &contours, sizeof(CvContour), CV_RETR_LIST,CV_CHAIN_APPROX_NONE ,cvPoint(0,0)); 

//creating empty sequence of CvPoint
CvSeq* seq = cvCreateSeq(CV_SEQ_ELTYPE_POINT/*| CV_SEQ_KIND_SET | CV_SEQ_FLAG_SIMPLE*/,sizeof(CvSeq),sizeof(CvPoint),storage1);

//populating seq with all contours
for(; contours!=0; contours = contours->h_next)
  for(int i=0;i<contours->total;i++)
     {  
         CvPoint* p;
        p = (CvPoint*)cvGetSeqElem (contours, i );
        cvSeqPush(seq,p);   
      }

//bounding box and drawing
CvBox2D bbox=cvMinAreaRect2(seq, NULL );
cvEllipseBox(color,bbox,cvScalarAll(0),5,8,0);

hope this helps.