Matthew goes on to explain a couple of tonal scales that can be used to bring extra visual and emotional impact to your images by working with the balance of light and dark. He provides a number of step by step examples. Once you can master tonal value adjustment in your head, you are then freed from the constraints your source material may have on your final work.
For us with the access to image manipulation software such as Gimp or Photoshop he shows us how we can process the images and play about with the tonal ranges in a more must have it now digital fashion. Can you imagine doing this with manually painting your own examples and the time it would take? But perhaps then we’d learn it more thoroughly.
Even if you are short on time to paint your own example exercises, it is well worth the time to read the article.