title: PIL, Image.fromarray make noises
body: <p><a href="https://i.stack.imgur.com/8C1ww.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8C1ww.png" alt="enter image description here"></a></p>
  
  <p>i am doing conversion between images(alphabet I) and arr(np.array)<br>
  the mode is 'L', grayscale img.<br>
  there is no pixels like noise in np.array but when i did conversion.
  <code>
  img = Image.fromarray(arr) 
  img.save(path)
  </code></p>
  
  <p>then there are noises in saved img.<br>
  ex> arr[0] components are all 255 but there is some noise in the first line of saved image.</p>
  
  <p>i don't know why noise happens in images.</p>