title: OpenCV return keypoints coordinates and area from blob detection, Python
body: <p>I followed a blob detection example (using <code>cv2.SimpleBlobDetector</code>) and successfully detected the blobs in my binary image. But then I don't know how to extract the coordinates and area of the keypoints. Here are the code for the blob detections:</p>
  
  <pre><code># I skipped the parameter setting part. 
      blobParams = cv2.SimpleBlobDetector_Params()
      blobVer = (cv2.__version__).split('.')
      if int(blobVer[0]) &lt; 3:
          detector = cv2.SimpleBlobDetector(blobParams)
      else:
          detector = cv2.SimpleBlobDetector_create(blobParams)
  
      # Detect Blobs
      keypoints_black = detector.detect(255-black_blob)
      trans_blobs = cv2.drawKeypoints(gray_video_crop, \
          keypoints_white, np.array([]), (0,0,255), cv2.DRAW_MATCHES_FLAGS_DRAW_RICH_KEYPOINTS)
  </code></pre>
  
  <p>So the variable <code>keypoints_black</code> contains the information of the blob(s). When I printed the variable it looked something like this (2 blobs were found):</p>
  
  <pre><code>KeyPoint 0x10b10b870, KeyPoint 0x10b1301b0
  </code></pre>
  
  <p>So how to I get the coordinates of the centre of mass of the keypoints and their area so that I can send them as osc messages for interaction. </p>