code: def zstack_proxy_iterator(self, s=0, c=0, t=0):
          
          for proxy_image in self:
              if proxy_image.in_zstack(s=s, c=c, t=t):
                  yield proxy_image
docs: Return iterator of :class:`jicimagelib.image.ProxyImage` instances in the zstack.
          
          :param s: series
          :param c: channel
          :param t: timepoint
          :returns: zstack :class:`jicimagelib.image.ProxyImage` iterator