private void writeNetscapeExtension(OutputStream os) throws IOException {
		/* n.b. most software seems to interpret the count as a repeat count */
		/* (i.e., interations beyond 1) rather than as an iteration count */
		/* (thus, to avoid repeating we have to omit the whole extension) */

		os.write('!');                 /* GIF Extension Introducer */
		os.write(0xff);                /* Application Extension Label */

		os.write(11);                  /* application ID block size */
		Gif89Put.ascii("NETSCAPE2.0", os);  /* application ID data */

		os.write(3);                   /* data sub-block size */
		os.write(1);                   /* a looping flag? dunno */

		/* we finally write the relevent data */
		Gif89Put.leShort(loopCount > 1 ? loopCount - 1 : 0, os);

		os.write(0);                   /* block terminator */
	}