title: Using PIL to turn a RGB image into a pure black and white image
body: <p>I'm using the Python Imaging Library for some very simple image manipulation, however I'm having trouble converting a greyscale image to a monochrome (black and white) image. If I save after changing the image to greyscale (convert('L')) then the image renders as you would expect. However, if I convert the image to a monochrome, single-band image it just gives me noise as you can see in the images below. Is there a simple way to take a colour png image to a pure black and white image using PIL / python?</p>
  <pre><code>from PIL import Image 
  import ImageEnhance
  import ImageFilter
  from scipy.misc import imsave
  image_file = Image.open(&quot;convert_image.png&quot;) # open colour image
  image_file= image_file.convert('L') # convert image to monochrome - this works
  image_file= image_file.convert('1') # convert image to black and white
  imsave('result_col.png', image_file)
  </code></pre>
  <p><img src="https://i.imgur.com/mB96s.png" alt="Original Image" title="original image" />
  <img src="https://i.imgur.com/O5HoK.png" alt="Converted Image" title="converted image" /></p>