title: Erosion and dilation in Python OpenCV returns white
body: <p>I am trying to use dialation and ertion</p>
  
  <p>For example, like so:</p>
  
  <pre><code>dialated = cv2.dilate(edgesCopy, cv2.getStructuringElement(cv2.MORPH_CROSS,(3,3)), iterations = 1)
  </code></pre>
  
  <p>The input is a uint8 image that has only values of 0 and 255, as came out of</p>
  
  <pre><code>threshold, thresholdedEdges = cv2.threshold(edges, 220, 255, cv2.THRESH_BINARY_INV);
  </code></pre>
  
  <p>The output, however is just a white image. I fail to understand the reason.</p>
  
  <p>The entire code is</p>
  
  <pre><code>   imageSize = img.shape
      if len(imageSize) != 2:#color
          print "got a color image - quitting"
          return
  
      cv2.imshow("im1", img)
      cv2.moveWindow("im1", 60, 50)
  
      gaussianBlur = cv2.GaussianBlur(img, (5, 5), 0)
      # cv2.imshow("gaussianBlur", gaussianBlur)
      # cv2.moveWindow("gaussianBlur", 260, 50)
  
      medianBlur = cv2.medianBlur(gaussianBlur, 5)
      # cv2.imshow("medianBlur", medianBlur)
      # cv2.moveWindow("medianBlur", 460, 50)
  
      minGradientValueThreshold = 225
      maxGradientValueThreshold = 150
      edges = cv2.Canny(medianBlur, minGradientValueThreshold, maxGradientValueThreshold)
      cv2.imshow("edges", edges)
      cv2.moveWindow("edges", 660, 50)
  
      # Threshold.
      # Set values equal to or above 220 to 0.
      # Set values below 220 to 255.
  
      threshold, thresholdedEdges = cv2.threshold(edges, 220, 1, cv2.THRESH_BINARY_INV);
  
      edgesCopy = thresholdedEdges.copy()
  
      #close the edges before floodfilling, to avoid filing the background
      # closing = cv2.morphologyEx(floodFilledImage, cv2.MORPH_CLOSE, cv2.getStructuringElement(cv2.MORPH_RECT,(5,5)))  DOESN'T WORK
      dialated = cv2.dilate(edgesCopy, cv2.getStructuringElement(cv2.MORPH_CROSS,(3,3)), iterations = 1)
  
      cv2.imshow("dialated", dialated)
      cv2.moveWindow("dialated", 60, 250)
  
      eroded = cv2.erode(dialated, cv2.getStructuringElement(cv2.MORPH_CROSS,(3,3)), iterations = 1)
  
      closing = eroded
  
      cv2.imshow("closing", closing)
      cv2.moveWindow("closing", 60, 250)
  </code></pre>