title: What does it mean when there are four tuples in a tf.pad function
body: <p>I have this piece of code:</p>
  
  <pre><code>    padded_inputs = tf.pad(inputs, [[0, 0], [0, 0], [pad_beg, pad_end], [pad_beg, pad_end]])
  </code></pre>
  
  <p>It is for an image. I don't understand why there are four tuples since an image has width, height, and three color channels.</p>