static BWImage getAlphaChannel(BufferedImage src) {
  int w = src.getWidth();
  int h = src.getHeight();

  BWImage alpha = new BWImage(w, h);
  for y to h: for x to w: {
    //int a = (srcBuffer[i] >> 24) & 0xff;
    //int a = srcBuffer[i] & 0xff;
    int a = (src.getRGB(x, y) >> 24) &0xff;
    alpha.setByte(x, y, a);
    //print(intToHex= (srcBuffer[i]));
  }
  ret alpha;
}