title: PyTorch: How do the means and stds get calculated in the Transfer Learning tutorial?
body: <p>I'm going through the PyTorch Transfer Learning tutorial at: <a href="http://pytorch.org/tutorials/beginner/transfer_learning_tutorial.html#visualize-a-few-images" rel="noreferrer">link</a></p>
  
  <p>In the data augmentation stage, there is the following step to normalize images:</p>
  
  <pre><code>transforms.Normalize([0.485, 0.456, 0.406], [0.229, 0.224, 0.225])
  </code></pre>
  
  <p>I can understand why it's doing this but I can't find how the mean and std values get calculated? I tried to calculate the mean on the train data set and the mean values are:</p>
  
  <pre><code>array([ 0.11727478,  0.04542569, -0.28624609], dtype=float32)
  </code></pre>