private Picture mirrorHoriz(Picture pix){
    Pixel topPixel = null; 
    Pixel bottomPixel = null; 
     
    int midpoint = pix.getHeight()/2; 
    int height = pix.getHeight(); 
     
    for(int col = 0; 
        < pix.getWidth(); 
        col++){ 
      for(int row = 0; 
          row < midpoint; 
          row++){ 
        topPixel = pix.getPixel(col,row);
        bottomPixel = 
          pix.getPixel(col,height-1-row);
        bottomPixel.setColor( 
                    topPixel.getColor());
      }//end inner loop 
    }//end outer loop 
 
    return pix; 
  }//end mirrorHoriz 
  //-----------------------------------//
   
}//end class Prob01Runner