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Editorial Team
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Asked: 2026-06-18T15:05:49+00:00

I am working on software using OpenCV in C++ environment. The objective is to

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I am working on software using OpenCV in C++ environment. The objective is to detect a boxing glove and draw a bounding box around gloves contours.

The problem I am running into is that the bounding box is drown more than once in fact multiple boxes are drawn. What I was trying to do over the past few days is to somehow eliminate the number of boxes drawn and have only one big bounding box drawn.

I was looking at some techniques to fill in the object int its whole which i believe would really help in this case.

Below I have posted the code i used to achieve the result displayed in the image:

vector<vector<Point> > contours;
vector<Vec4i> hierarchy;
vector<Vec3f> vecCircles;               
vector<Vec3f>::iterator itrCircles;

while(1)
{
    Mat frame;
    cap >> frame; // get a new frame from camera
    /////////////////////
    Mat imgHSV;
    cvtColor( frame, imgHSV, CV_BGR2HSV );
    ////////////////////
    Mat blur_out;
    GaussianBlur(imgHSV, blur_out, Size(1,1),2.0,2.0);
    ////////////////////
    Mat range_out;
    inRange(blur_out, Scalar(100, 100, 100), Scalar(120, 255, 255), range_out);
    ////////////////////
    findContours(range_out, contours, hierarchy, CV_RETR_TREE,  CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );

     /// Approximate contours to polygons + get bounding rects and circles
     vector<vector<Point> > contours_poly( contours.size() );
     vector<Rect> boundRect( contours.size() );
     vector<Point2f>center( contours.size() );
     vector<float>radius( contours.size() );

     for( int i = 0; i < contours.size(); i++ )
     { 
         approxPolyDP( Mat(contours[i]), contours_poly[i], 3, true );
         boundRect[i] = boundingRect( Mat(contours_poly[i]) );
     }

     /// Draw polygonal contour + bonding rects
     Mat drawing = Mat::zeros( range_out.size(), CV_8UC3 );
     for( int i = 0; i< contours.size(); i++ )
     {
         Scalar color = Scalar(255,0,255);
         drawContours( drawing, contours_poly, i, color, 1, 8, vector<Vec4i>(), 0, Point() );
         rectangle( drawing, boundRect[i].tl(), boundRect[i].br(), color, 2, 8, 0 );          
     }

enter image description here

If anyone could suggest some tips or provide some source of information where i can find answers for my problem.

EDIT (quick update):

I managed to improve the output image quiet gradually to a point am quiet happy with the result. The Key was the usage of erode & dilation as well as in my findContours() function. I changed the CV_RETR_TREE to CV_RETR_EXTERNAL. There were a few other minor things i tackled but the result is good:

enter image description here

Dont know if i should write this here or open new thread….But now I need some help with component labeling and extracting parameters such as center points and area. 🙂

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1 Answer

  1. Editorial Team

    You currently draw a bounding box around each contour, and findContour will find a contour around each connected white or black component, of which there are many in your picture.

    So the first thing I would do is filter all that noise with some morphological operations on the thresholded image: do some opening and closing, both of which are combinations of dilation and erosion.

    In your case something like cvDilate (2 times); cvErode(4 times); cvDilate(2 times)

    This should merge all white blobs into one smooth blob, but the black hole in the middle will remain.
    You could find the right one by size, but it is easier to call findContours with the CV_RETR_EXTERNAL instead of CV_RETR_TREE, then it will only return the outermost contours.

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