title: How can i know if a contour is open or closed in opencv?
body: <p>How can i know if a contour taken from 'find contour' function is open or closed in opencv?</p>
  
  <p><strong>UPDATE</strong></p>
  
  <p>I tried to apply isContourConvex to this image: <a href="https://docs.google.com/file/d/0ByS6Z5WRz-h2RXdzVGtXUTlPSGc/edit?usp=sharing" rel="nofollow">https://docs.google.com/file/d/0ByS6Z5WRz-h2RXdzVGtXUTlPSGc/edit?usp=sharing</a></p>
  
  <p>i extractes contour with greatest area
  and return false.
  I change, maybe, contour extraction, dilating?</p>
  
  <pre><code>nomeimg = 'Riscalate2/JPEG/e (5).jpg'
  
  img = cv2.imread(nomeimg)
  
  gray = cv2.imread(nomeimg,0)#convert grayscale adn binarize
  
  element = cv2.getStructuringElement(cv2.MORPH_CROSS,(6,6)) 
  graydilate = cv2.erode(gray, element) #imgbnbin
  
  cv2.imshow('image',graydilate)
  cv2.waitKey(0)
  
  ret,thresh = cv2.threshold(graydilate,127,255,cv2.THRESH_BINARY_INV)   # binarize
  
  imgbnbin = thresh
  cv2.imshow('bn',thresh)
  cv2.waitKey()
  
  #element = cv2.getStructuringElement(cv2.MORPH_CROSS,(2,2))
  #element = np.ones((11,11),'uint8')
  
  
  contours, hierarchy = cv2.findContours(imgbnbin, cv2.RETR_TREE ,cv2.CHAIN_APPROX_SIMPLE)
  print(len(contours))
  
  
  # Take only biggest contour basing on area
  Areacontours = list()
  calcarea = 0.0
  unicocnt = 0.0
  for i in range (0, len(contours)):
      area = cv2.contourArea(contours[i])
      #print("area")
      #print(area)
      if (area &gt; 90 ):  #con 90 trova i segni e togli puntini
          if (calcarea&lt;area):
              calcarea = area
              unicocnt = contours[i]
  
  
  convex = cv2.isContourConvex(unicocnt)
  print("convex")
  print(convex)
  </code></pre>