Question

Currently I am developing image processing project and I’m using javacv to develop image processing components. I was able to extract some interesting parts of a image and now I need to read the x and y coordinates of those objects.
This is the image that I haveextracted

And I need to identify those objects and draw square around those objects. I went through some tutorials and try to identify objects using following code.

    IplImage img="sourceimage";
    CvSize sz = cvSize(img.width(), img.height());
    IplImage gry=cvCreateImage(sz, img.depth(), 1);
    cvCvtColor(img, gry, CV_BGR2GRAY);
    cvThreshold(gry, gry, 200, 250, CV_THRESH_BINARY);


    CvMemStorage mem = CvMemStorage.create();
    CvSeq contours = new CvSeq();
    CvSeq ptr = new CvSeq();
    cvFindContours(gry, mem, contours, Loader.sizeof(CvContour.class) , CV_RETR_CCOMP, CV_CHAIN_APPROX_SIMPLE, cvPoint(0,0));

    CvRect boundbox;

    for (ptr = contours; ptr != null; ptr = ptr.h_next()) {
        boundbox = cvBoundingRect(ptr, 0);
        if(boundbox.height()>10||boundbox.height()>10){
            cvRectangle( gry, cvPoint( boundbox.x(), boundbox.y() ), cvPoint( boundbox.x() + boundbox.width(), boundbox.y() + boundbox.height()),CvScalar.BLUE, 0, 0, 0 );
            System.out.println(boundbox.x()+", "+boundbox.y());
        }
    }
    cvShowImage("contures", gry);
    cvWaitKey(0);

But it doesn’t draw as rectangle around the objects. I would like to know whether I can use cvFindContours method to identify those objects ? Please can some one explain how to archive my objective using javacv/opencv?

Answer 1

Try to go through following code and it will give answer for your question.

    IplImage img=cvLoadImage("pathtosourceimage");
    CvSize cvSize = cvSize(img.width(), img.height());
    IplImage gry=cvCreateImage(cvSize, img.depth(), 1);
    cvCvtColor(img, gry, CV_BGR2GRAY);
    cvThreshold(gry, gry, 200, 255, CV_THRESH_BINARY);
    cvAdaptiveThreshold(gry, gry, 255, CV_ADAPTIVE_THRESH_MEAN_C, CV_THRESH_BINARY_INV, 11, 5);

    CvMemStorage storage = CvMemStorage.create();
    CvSeq contours = new CvContour(null);

    int noOfContors = cvFindContours(gry, storage, contours, Loader.sizeof(CvContour.class), CV_RETR_CCOMP, CV_CHAIN_APPROX_NONE, new CvPoint(0,0));

    CvSeq ptr = new CvSeq();

    int count =1;
    CvPoint p1 = new CvPoint(0,0),p2 = new CvPoint(0,0);

    for (ptr = contours; ptr != null; ptr = ptr.h_next()) {

        CvScalar color = CvScalar.BLUE;
        CvRect sq = cvBoundingRect(ptr, 0);

            System.out.println("Contour No ="+count);
            System.out.println("X ="+ sq.x()+" Y="+ sq.y());
            System.out.println("Height ="+sq.height()+" Width ="+sq.width());
            System.out.println("");

            p1.x(sq.x());
            p2.x(sq.x()+sq.width());
            p1.y(sq.y());
            p2.y(sq.y()+sq.height());
            cvRectangle(img, p1,p2, CV_RGB(255, 0, 0), 2, 8, 0);
            cvDrawContours(img, ptr, color, CV_RGB(0,0,0), -1, CV_FILLED, 8, cvPoint(0,0));
            count++;

    }

    cvShowImage("contures",img);
    cvWaitKey(0);

This is the output that I got for your given image.