title: Convert a raster image into a polygon using QGis (or another method)
body: <p>I want to convert several images into polygon shp files using QGis (Quantum GIS 1.6).</p>
  
  <p>I need to do edge detection AND differentiate between several different colors of lines (red, green, yellow and black). I need good edge detection as my images are scanned in at 200 DPI.</p>
  
  <p>I'm open to other suggestions that don't involve QGis. Could I use Photoshop or would Arcgis do a better job of this?</p>