title: How to convert a UIImage into a black and white UIImage in Objective-C?
body: <p>I don't want grayscale but rather for the darker colors to turn black and the lighter to turn white. How can I do this? I found something that looks promising here <a href="https://stackoverflow.com/questions/4401567/getting-a-black-and-white-uiimage-not-grayscale">Getting a Black and White UIImage (Not Grayscale)</a> but the line below in the code gives me an error that I can not fix. </p>
  
  <pre><code>CGContextRef contex = CreateARGBBitmapContext(image.size); 
  </code></pre>