title: Should I substract imagenet pretrained inception_v3 model mean value at inception_v3.py keras?
body: <pre><code>def preprocess_input(x):
  x /= 255.
  x -= 0.5
  x *= 2.
  return x
  </code></pre>
  
  <p>&emsp;I am using <strong>keras</strong> inception_v3 imagenet pretrained model(<a href="https://github.com/fchollet/keras/blob/master/keras/applications/inception_v3.py" rel="nofollow noreferrer">inception_v3.py</a>) to finetune on my own dataset.<br>
  &emsp;When I want to <strong>subtract the imagenet mean value [123.68, 116.779, 103.939] and reverse axis RGB to BGR</strong> as we often do, I find that the author provided a _preprocess_input()_ function at the end.I am confused about this.  </p>
  
  <p>&emsp; Should I use the provided function <em>preprocess_input()</em> <strong>or</strong> subtract mean value and reverse axis as usual?<br>
  &emsp; Thanks lot.</p>