title: Converting an image with simple shapes to polygons
body: <p>I have a simple GIS layer image exported from an ArcGIS server, which I now want to convert back to polygons. 
  What is the best method to go about doing that?</p>
  
  <ol>
  <li>Write my own script (what's best then- triangulation? line/edge tracing?)</li>
  <li>Use some tool? (opencv? something else?)</li>
  </ol>
  
  <p><img src="https://i.stack.imgur.com/xmSgp.png" alt="png image of polygons (each color represents a different polygon)"></p>