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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def save_images(self, directory=None, axis='z', channel=None, global_norm=True, image_format='PNG'):
 """See cloudvolume.lib.save_images for more information."""

    if directory is None:
      directory = os.path.join('./saved_images', self.dataset_name, self.layer, str(self.mip), self.bounds.to_filename())

    return save_images(self, directory, axis, channel, global_norm, image_format)