code: def get_scale(self):
          
          if self.exposure is not None:
              return self.exposure
  
          raw = initializers.load_tiff(self.filename)
          return raw.min(), raw.max()
docs: If exposure was not set in the __init__, get the exposure associated
          with this RawImage so that it may be used in other
          :class:`~peri.util.RawImage`. This is useful for transferring exposure
          parameters to a series of images.
  
          Returns
          -------
          exposure : tuple of floats
              The (emin, emax) which get mapped to (0, 1)