title: Clarifying np.unique() values in image processing
body: <p>Stupid question. I have an image, and I am reading it in a grayscale through python using the <code>cv2</code> library like this:</p>
  
  <pre><code>image_gray = cv2.imread(image, cv2.IMREAD_GRAYSCALE)
  </code></pre>
  
  <p>When I try to find the different color values in this image, I use  the following:</p>
  
  <pre><code>np.unique(image_gray.flatten())
  </code></pre>
  
  <p>This returns [58, 255]. What are these numbers representing? How do I get the equivalent RGB values?  </p>