private void writeGraphicControlExtension(OutputStream os, boolean epluribus,
			int itransparent) throws IOException {
		int transflag = itransparent == -1 ? 0 : 1;
		if (transflag == 1 || epluribus) {  /* using transparency or animating ? */
			os.write('!');                   /* GIF Extension Introducer */
			os.write(0xf9);                  /* Graphic Control Label */
			os.write(4);                     /* subsequent data block size */
			os.write((disposalCode << 2) | transflag); /* packed fields (1 byte) */
			Gif89Put.leShort(csecsDelay, os);  /* delay field (2 bytes) */
			os.write(itransparent);          /* transparent index field */
			os.write(0);                     /* block terminator */
				}
			}