def is_consecutive(self):
        """
        Determine whether or not the non-zero labels in the segmentation
        image are consecutive (i.e. no missing values).
        """

        if (self.labels[-1] - self.labels[0] + 1) == self.nlabels:
            return True
        else:
            return False
Determine whether or not the non-zero labels in the segmentation
        image are consecutive (i.e. no missing values).