title: Contour Arrays in OpenCV
body: <p>In another user's post, they discussed how they were having trouble using OpenCV's Hough Circle Transform to detect and draw over each ring on a bull target <a href="https://stackoverflow.com/questions/32287032/circular-hough-transform-misses-circles">here</a>. A proposed solution was to instead using contours to locate each circle. When I attempted the same thing, my result was exactly what I was looking for; the only problem is that the program I'm attempting to create needs a series of circles, one on each ring, so that I may then calculate the distance from the center and therefore the particular ring where a given point exists.</p>
  
  <p>Following the code if the mentioned post, I have the following:</p>
  
  <pre><code>import cv2
  import numpy as np
  
  image = cv2.imread('bull.png')
  image_copy = cv2.cvtColor(image, cv2.COLOR_RGB2GRAY)
  grayscaled_image = cv2.cvtColor(image_copy, cv2.COLOR_GRAY2BGR)
  
  cv2.imshow("confirm", grayscaled_image)
  cv2.waitKey(0)
  cv2.destroyAllWindows()
  
  _,contours,_  = cv2.findContours(255 - image_copy, cv2.RETR_LIST, cv2.CHAIN_APPROX_NONE)
  print(contours)
  
  cv2.drawContours(image, contours, -1, color=(0,255,0), thickness=1)
  
  cv2.imshow("detected circles", image)
  cv2.waitKey(0)
  cv2.destroyAllWindows()
  </code></pre>
  
  <p>Which gives me the same results as shown in the linked post.</p>
  
  <p>And this is great. I love the progress. However, I initially tried using the same method that the linked poster did because I liked the coordinate and radius information provided by the circles.</p>
  
  <p>I found in one of <a href="http://docs.opencv.org/master/dd/d49/tutorial_py_contour_features.html#gsc.tab=0" rel="nofollow noreferrer">OpenCV's tutorials</a> that you can contain a contour with a circle, rectangle, or ellipse. The tutorial is rather easy to follow for an individual contour, but in my code, I have no idea what <code>_,contours,_</code> means. Is it some sort of array? How do I access the individual contours? When I tried printing the variable, it gave me close to 4,000 lines. I won't post them here, of course, but they appeared to be sets of coordinates. </p>
  
  <p>So my question is: How can I go about converting this grouping of contours into more manageable circles?</p>