title: Tensorflow VarLenFeature vs FixedLenFeature
body: <p>I was trying to save images of different sizes into tf-records. I found that even though the images have different sizes, I can still load them with <code>FixedLenFeature</code>. </p>
  
  <p>By checking the docs on <code>FixedLenFeature</code> and <code>VarLenFeature</code>,  I found the difference seems to be that <code>VarLenFeauture</code> returns a sparse tensor.</p>
  
  <p>Could anyone illustrate some situations one should use <code>FixedLenFeature</code> or <code>VarLenFeature</code>?</p>