detect blob over other blob

I use OpenCV and cvblob library to play with blob.

Now I want to detect blob in this particular case.

The problem or the difficulty in this case is there are two blobs over a bigger one and other 开发者_运维知识库blob that overlap a part of the bigger one.

In cvblob library to detect a blob you must have a binary image.

I think i need to create two or more image to segment color uniform blobs and then binarize them to obtain all the blobs in the image.

How can i do that.

thanks in advance

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I'm quite a beginner in OpenCV but I guess that, for that particular case, you should work with cvFindContours with the CV_RETR_EXTERNAL flag (with the CV_RETR_TREE, your yellow blob would be IN the blue one) instead of using cvblob.

It depends if you want to track them or not (cvblob offers a quick and efficient way to track blobs, instead of having to implement camshift).

CvMemStorage* storage = cvCreateMemStorage(0);
    CvSeq* firstContour = cvCreateSeq(CV_SEQ_ELTYPE_POINT, sizeof(CvSeq), sizeof(CvPoint), storage);

    cvFindContours(image, storage, &firstContour, sizeof(CvContour), CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE);




    // S'il y a un contour
    if(firstContour != 0) {

        for( CvSeq* c = firstContour; c != NULL; c = c->h_next ) {

                    for(int i = 0; i < c->total; ++i) {                    

                        // Get each point of the current contour
                        CvPoint* pt = CV_GET_SEQ_ELEM(CvPoint, c, i);

                        double x = pt->x;
                        double y = pt->y;

                    }
          }
      }

With the information given by the contour you can find easily the centroid, angle and bounding box of your blob.

Tracking these blob might be more difficult as cvblob doesn't like overlapping blobs (as I can see). You may have to implement your own tracking method.