title: Convert RGB to black OR white
body: <p>How would I take an RGB image in Python and convert it to black and white? Not grayscale, I want each pixel to be either fully black (0, 0, 0) or fully white (255, 255, 255).</p>
  <p>Is there any built-in functionality for getting it done  in the popular Python image processing libraries? If not, would the best way be just to loop through each pixel, if it's closer to white set it to white, if it's closer to black set it to black?</p>