title: OpenCV Python: cv2.findContours - ValueError: too many values to unpack
body: <p>I'm writing an opencv program and I found a script on another stackoverflow question: <a href="https://stackoverflow.com/questions/14752006/computer-vision-masking-a-human-hand/14756351#14756351">Computer Vision: Masking a human hand</a></p>
  
  <p>When I run the scripted answer, I get the following error:</p>
  
  <pre><code>Traceback (most recent call last):
      File "skinimagecontour.py", line 13, in &lt;module&gt;
      contours, _ = cv2.findContours(skin_ycrcb, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
  ValueError: too many values to unpack
  </code></pre>
  
  <p>The code:</p>
  
  <pre><code>import sys
  import numpy
  import cv2
  
  im = cv2.imread('Photos/test.jpg')
  im_ycrcb = cv2.cvtColor(im, cv2.COLOR_BGR2YCR_CB)
  
  skin_ycrcb_mint = numpy.array((0, 133, 77))
  skin_ycrcb_maxt = numpy.array((255, 173, 127))
  skin_ycrcb = cv2.inRange(im_ycrcb, skin_ycrcb_mint, skin_ycrcb_maxt)
  cv2.imwrite('Photos/output2.jpg', skin_ycrcb) # Second image
  
  contours, _ = cv2.findContours(skin_ycrcb, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
  for i, c in enumerate(contours):
      area = cv2.contourArea(c)
      if area &gt; 1000:
          cv2.drawContours(im, contours, i, (255, 0, 0), 3)
  cv2.imwrite('Photos/output3.jpg', im)
  </code></pre>
  
  <p>Any help is appreciated!</p>