private void writeImageDescriptor(OutputStream os) throws IOException {
		os.write(',');                       /* Image Separator */
		Gif89Put.leShort(thePosition.x, os);
		Gif89Put.leShort(thePosition.y, os);
		Gif89Put.leShort(theWidth, os);
		Gif89Put.leShort(theHeight, os);
		os.write(isInterlaced ? 0x40 : 0);  /* packed fields (1 byte) */
	}