title: How to convert a 0, 255 binary image to a 0, 1 binary image?
body: <p>I have an image <code>img</code> in the form</p>
  <pre><code>array([[  0,   0,   0, ..., 255, 255, 255],
         [  0,   0,   0, ..., 255, 255,   0],
         [  0,   0,   0, ..., 255,   0,   0],
          ...,
         [  0,   0,   0, ...,   0,   0,   0],
         [  0,   0,   0, ...,   0,   0,   0],
         [  0,   0,   0, ...,   0,   0,   0]], dtype=uint8)
  </code></pre>
  <p>Is there any build in python function that convert images like that to 0,1 binarization?</p>