private Picture setOpacity(
                       Picture pic,double percentOpacity){

    int opacity = (int)(255*percentOpacity/100);
    int opacityMask = opacity << 24;

    for(int col = 0;col < butterflyWidth;col++){
      for(int row = 0;row < butterflyHeight;row++){
        //Get the pixel in basic int format.
        int basicPixel = pic.getBasicPixel(col,row);

        //Set the alpha value for the pixel.
        basicPixel = basicPixel & 0x00FFFFFF;
        basicPixel = basicPixel | opacityMask;

        //Set the modified pixel into tempPicture.
        tempPicture.setBasicPixel(col,row,basicPixel);
      }//end inner loop
    }//end outer loop

    return tempPicture;

  }//end setOpacity