title: Converting a grayscale image to black and white
body: <p>I have a grayscale image that only has the values <code>60</code> and <code>117</code>. How can I convert the image to only <code>black</code> and <code>white</code> without graylevels?</p>
  
  <p>I tried the <code>matlab</code> function <code>gray2ind</code>, but didn't get the expected output.</p>
  
  <p>Thanks.</p>