title: controll the size of image assigned to the background by ui colorpattern
body: <p>I assign an image to the background so the user can draw on it but the image always is not in the right size it takes like 1/3 of it and assigns it to the image view 
  the only way to bypass this is to make a canvas exactly the size of the image assigned like in PICSART app,
  does any one knows how to do this?</p>
  
  <pre><code>mainimageview.backgroundColor = UIColor(patternImage: "draw")
  </code></pre>
  
  <p>`</p>