title: how to make smooth and remove the white edge? Besides, why the black lines arise in my answer? How to solve it?
body: <p>Based on <a href="https://stackoverflow.com/questions/40124177/how-to-split-image-and-fill-different-color">Shai</a> and <a href="https://stackoverflow.com/questions/40133394/how-to-fill-gradient-color-from-light-yellow-to-dark-yellow/40134579?noredirect=1#comment67566319_40134579">Biguri</a>'s codes and comments, I have finished a color picture like this:</p>
  
  <p><a href="https://i.stack.imgur.com/qyknE.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qyknE.jpg" alt="enter image description here"></a></p>
  
  <p>A problem arises, how to remove the white edge and make it smooth? One solution may be to build <code>3x3</code> matrix or bigger and average. But the calculations should be large for every white-edge points. Or there may be some useful functions in <em>Matlab</em> to deal well with this problems?<a href="https://i.stack.imgur.com/2C24v.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2C24v.jpg" alt="enter image description here"></a></p>