code: def palette_image(self):
          
          if self.pimage is None:
              palette = []
              for i in range(self.NETSIZE):
                  palette.extend(self.colormap[i][:3])
  
              palette.extend([0] * (256 - self.NETSIZE) * 3)
  
              # a palette image to use for quant
              self.pimage = Image.new("P", (1, 1), 0)
              self.pimage.putpalette(palette)
          return self.pimage
docs: PIL weird interface for making a paletted image: create an image which
              already has the palette, and use that in Image.quantize. This function
              returns this palette image.