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

def zstack_proxy_iterator(self, s=0, c=0, t=0):
        """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
        """
        for proxy_image in self:
            if proxy_image.in_zstack(s=s, c=c, t=t):
                yield proxy_image