title: What is the 4th channel in an image?
body: <p>what does the column imply when randomly generating an image using <code>np.random.randint</code></p>
  
  <pre><code>img = np.random.randint(255, size=(4,4,3), dtype='uint8')
  </code></pre>
  
  <p>This creates a 4 by 4 pixel, with a matrix of 3 columns.</p>
  
  <pre><code>img = np.random.randint(255, size=(4,4,4), dtype='uint8')
  </code></pre>
  
  <p>This creates a 4 by 4 pixel, with a matrix of 4 columns.</p>
  
  <p>What is the job of the column in the matrix in this case?</p>