title: Normalization method for Convolutional Neural Network
body: <p>There have three common image data normalization methods, which are </p>
  
  <pre><code>1. X = (X - X.mean) / X.std
  2. X /= 255. # (based on formula: (X - min) / (max - min) which can converge data into [0, 1].)
  3. X = 2 * (X - min) / (max - min) - 1 # converge into [-1, 1]
  </code></pre>
  
  <p>I found in different CNN tutorials or posts, people may use one of them to normalize data. But I am a bit confused about them, how should I select one in different situations?</p>
  
  <p>Thanks for any explanations in advance.</p>