title: 9patch keep seeing the balck lines
body: <p>I try to make an image strechable with 9patch. But if I make a 9.png image and use it, I see the black lines I drew in 9patch.</p>
  
  <p><img src="https://i.stack.imgur.com/lFAjy.png" alt="9patch problem"></p>
  
  <p>How can I prevent this?</p>
  
  <p><img src="https://i.stack.imgur.com/m2kY5.png" alt="enter image description here"></p>