title: Convert 24bpp Bitmap to 1bpp
body: <p>I am trying to convert a small bitmap image.  I would like for any pixel that is not 100% white to be converted to black.  I have tried</p>
  
  <pre><code>Bitmap output = sourceImage.Clone(new Rectangle(0, 0, sourceImage.Width, sourceImage.Height), PixelFormat.Format1bppIndexed);
  </code></pre>
  
  <p>There are still a few lighter pixels that stay white in the 1bpp output.  What is the fastest way to achieve this conversion?  Can I modify the intensity threshold of the call to Clone()?</p>