title: What is the expected input range for working with Keras VGG models?
body: <p>I'm trying to use a pretrained VGG 16 from keras. But I'm really unsure about what the input range should be.   </p>
  
  <p>Quick answer, which of these color orders?</p>
  
  <ul>
  <li>RGB   </li>
  <li>BGR</li>
  </ul>
  
  <p>And which range? </p>
  
  <ul>
  <li>0 to 255?</li>
  <li>balanced from about -125 to about +130?</li>
  <li>0 to 1?</li>
  <li>-1 to 1?</li>
  </ul>
  
  <p>I notice <a href="https://github.com/fchollet/keras/blob/master/keras/applications/vgg16.py" rel="noreferrer">the file where the model is defined</a> imports an input preprocessor:</p>
  
  <pre><code>from .imagenet_utils import preprocess_input
  </code></pre>
  
  <p>But this preprocessor is never used in the rest of the file.</p>
  
  <p>Also, when I check the <a href="https://github.com/fchollet/keras/blob/master/keras/applications/imagenet_utils.py/#L11" rel="noreferrer">code for this preprocessor</a>, it has two modes: <code>caffe</code> and <code>tf</code> (tensorflow).    </p>
  
  <p>Each mode works differently. </p>
  
  <p>Finally, I can't find consistent documentation on the internet. </p>
  
  <p>So, what is the best range for working? To what range are the model weights trained?</p>