title: Pascal VOC Class Segmentation: Ground-truth pixel labeling for training
body: <p>I just started to work on the Pascal VOC segmentation dataset. But I have trouble understanding the colour coding they have used in the ground labeling. I assumed pixels would be annotated 1 through 20 for each class but what I have got are 8 bit deep png images with pixel values (0-255). </p>
  
  <p>For a certain pixel belonging to <code>aeroplane</code> class in <code>2007_000033.png</code>, I get the values: (128, 0, 0); while another pixel belonging to <code>train</code> class in <code>2007_000123.png</code>, gives the values : (128, 0, 192) and so on.</p>
  
  <p>How do I differentiate them in different classes and do a one-hot encoding? Do I need to specify pixel values for each class (like searching pixels with (128, 0, 0) and encode them as 1 for class <code>aeroplane</code>)?</p>
  
  <p>Sorry, I see a few similar questions on SO but nothing helped me. Thanks.</p>