private void writeImageDescriptor(OutputStream os, int imageWidth, int imageHeight, int imageLeftPosition, int imageTopPosition, int colorTableSize) throws Exception {
		byte imageDescriptor[] = new byte[10];
		imageDescriptor[0] = IMAGE_SEPARATOR;// Image separator ","
		imageDescriptor[1] = (byte)(imageLeftPosition&0xff);// Image left position
		imageDescriptor[2] = (byte)((imageLeftPosition>>8)&0xff);
		imageDescriptor[3] = (byte)(imageTopPosition&0xff);// Image top position
		imageDescriptor[4] = (byte)((imageTopPosition>>8)&0xff);
        imageDescriptor[5] = (byte)(imageWidth&0xff);
		imageDescriptor[6] = (byte)((imageWidth>>8)&0xff);
		imageDescriptor[7] = (byte)(imageHeight&0xff);
		imageDescriptor[8] = (byte)((imageHeight>>8)&0xff);
		imageDescriptor[9] = (byte)0x20;//0b00100000 - Packed fields
		
		if(colorTableSize >= 0) // Local color table will follow
			imageDescriptor[9] |= (1<<7|colorTableSize);
		
		os.write(imageDescriptor, 0, 10);
	}
Write out a zero length data sub-block
subs/gif-revert/src/main/java/com/engineer/gif/revert/lib/AnimatedGIFWriter.java