return (int) ((generateMask (3) & rgb[pixel]) >> (3 * pixel_bits));
return (0xFF000000 & rgb[pixel]) >> 24;
  public final int getAlpha (int pixel)  {    if (opaque || pixel >= map_size)      return 255;        return (int) ((generateMask (3) & rgb[pixel]) >> (3 * pixel_bits));		}