@classmethod
def instance_to_filename(klass, img, filename):
    """ Save `img` in our own format, to name implied by `filename`

        This is a class method

        Parameters
        ----------
        img : ``any FileBasedImage`` instance

        filename : str
           Filename, implying name to which to save image.
        """
    img = klass.from_image(img)
    img.to_filename(filename)
