static byte[] imagePixelsToRGBAWithSize(BufferedImage etc img) {
  if (img == null) null;
  int w = img.getWidth(), h = img.getHeight(), n = w*h;
  byte[] out = new[(n+2)*4];
  
  // store width and height
  intToBytes_inArray_littleEndian(w, out, 0);
  intToBytes_inArray_littleEndian(h, out, 4);
  
  // store pixels
  copyIntArrayToByteArray_littleEndian(pixelsOfBufferedImage(img), out, 8);
  ret out;
}