private Picture mirrorUpperQuads(Picture pix){

    Pixel leftPixel = null;
    Pixel rightPixel = null;
    int midpoint = pix.getWidth()/2;
    int width = pix.getWidth();

    for(int row = 0;row < pix.getHeight()/2;
                                     row++){
      for(int col = 0;col < midpoint;col++){
        leftPixel = pix.getPixel(col,row);
        rightPixel =
            pix.getPixel(width-1-col,row);
        rightPixel.setColor(
            leftPixel.getColor());
      }//end inner loop
    }//end outer loop

    return pix;
  }//end mirrorUpperQuads