threshold(gr, bw, 0, 255, CV_THRESH_BINARY | CV_THRESH_OTSU)
vector < vector < Point >> contours
vector < Vec4i > hierarchy
findContours(bw, contours, hierarchy, CV_RETR_CCOMP, CV_CHAIN_APPROX_SIMPLE,
    Point(0, 0))
Detection of irregular shapes using houghcircle function opencv python