void encode(OutputStream os, boolean epluribus, int color_depth,
                  int transparent_index) throws IOException
      {
        writeGraphicControlExtension(os, epluribus, transparent_index);
        writeImageDescriptor(os);
        new GifPixelsEncoder(
          theWidth, theHeight, ciPixels, isInterlaced, color_depth
        ).encode(os);
      }