title: iOS: How to apply custom image filter with white background
body: <p>I want to do something like this: </p>
  
  <p><img src="https://i.stack.imgur.com/9Jz5n.jpg" alt="enter image description here"></p>
  
  <p>Take an image with white background, and apply black colour only in the rest of the image.</p>
  
  <p>How can I do this with iOS?</p>