title: crop image from polygon_perimeter
body: <p>I am attempting to crop the image.
  I have created a polygon around the part I want cropped.</p>
  <pre><code>xs = []
  ys = []
  for props in measurements:
      minr, minc, maxr, maxc = props.bbox
      by = (minc , maxc, maxc, minc, minc)
      bx = (minr, minr, maxr, maxr, minr)
      xs.append(bx)
      ys.append(by)
      
      
  r = xs[0] 
  c = ys[0] 
  
  
  rr,cc = draw.polygon_perimeter(r ,c)
  img_blob[rr,cc] = 1
  cool = img_blob[rr,cc]
  
  [rows, columns] = np.where(cool)
  row1 = min(rows)
  row2 = max(rows)
  col1 = min(columns)
  col2 = max(columns)
  
  
  cropped = img_blob[row1 : row2, col1:col2]
  plt.imshow(cropped)
  </code></pre>
  <p>with the code above i am getting the</p>
  <pre><code>ValueError to be 'not enough values to unpack (expected 2, got 1)'
  </code></pre>
  <p>How can I get only where the <code>polygon_perimeter</code> is so that I can crop it according to that?</p>
  <p>I cannot use <code>cv2</code> or <code>PIL</code>, only <code>skimage</code> or <code>numpy</code></p>