code: def do_region(self, x, y, w, h):
          
          if (x is None):
              self.logger.debug("region: full (nop)")
          else:
              self.logger.debug("region: (%d,%d,%d,%d)" % (x, y, w, h))
              self.image = self.image.crop((x, y, x + w, y + h))
              self.width = w
              self.height = h
docs: Apply region selection.