OpenCV - Detect hand-drawing shapes

Question

Could OpenCV detect the geometric shapes which is drawn by hand as below? The shape can be a rectangle, triangle, circle, curve, arc,polygon,... I am going to develop an and

Answer 1

Well, I tried it in a harry. Normally you need to skeletonize the input. Anyway. You can reason about the shapes based on their points. Normally a square has 4, a triangle 3, etc. Effort results:

Canny results:

Polygonal approximation:

Console output:

contour points:11
contour points:6
contour points:4 
contour points:5

Here is the code:

    Mat src=imread("WyoKM.png");
    Mat src_gray(src.size(),CV_8UC1);
    if (src.empty()) exit(-10);
    imshow("img",src);

    /// Convert image to gray and blur it
    cvtColor( src, src_gray, CV_BGR2GRAY );
    threshold(src_gray,src_gray,100,255,src_gray.type());
    imshow("img2",src_gray);

    Mat canny_output;
    vector > contours;
    vector hierarchy;

    /// Detect edges using canny
    int thresh=100;
    Canny( src_gray, canny_output, thresh, thresh*2, 3 );
    imshow("canny",canny_output);
    imwrite("canny.jpg",canny_output);

    /// Find contours
    findContours( canny_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );

    // testing the approximate polygon
    cv::Mat result(src_gray.size(),CV_8U,cv::Scalar(255));
    for(int i=0;i poly;
        poly.clear();
        cv::approxPolyDP(cv::Mat(contours[i]),poly,
            5, // accuracy of the approximation
            true); // yes it is a closed shape

        // Iterate over each segment and draw it
        std::vector::const_iterator itp= poly.begin();
        cout<<"\ncontour points:"<