Return a (cx, cy) 2-tuple representing the native dimensions of this
        image scaled by applying the following rules to *width* and *height*.
        If both *width* and *height* are specified, the return value is
        (*width*, *height*); no scaling is performed. If only one is
        specified, it is used to compute a scaling factor that is then
        applied to the unspecified dimension, preserving the aspect ratio of
        the image. If both *width* and *height* are |None|, the native
        dimensions are returned. The native dimensions are calculated using
        the dots-per-inch (dpi) value embedded in the image, defaulting to 72
        dpi if no value is specified, as is often the case. The returned
        values are both |Length| objects.

def scaled_dimensions(self, width=None, height=None):
        """
        Return a (cx, cy) 2-tuple representing the native dimensions of this
        image scaled by applying the following rules to *width* and *height*.
        If both *width* and *height* are specified, the return value is
        (*width*, *height*); no scaling is performed. If only one is
        specified, it is used to compute a scaling factor that is then
        applied to the unspecified dimension, preserving the aspect ratio of
        the image. If both *width* and *height* are |None|, the native
        dimensions are returned. The native dimensions are calculated using
        the dots-per-inch (dpi) value embedded in the image, defaulting to 72
        dpi if no value is specified, as is often the case. The returned
        values are both |Length| objects.
        """
        if width is None and height is None:
            return self.width, self.height

        if width is None:
            scaling_factor = float(height) / float(self.height)
            width = round(self.width * scaling_factor)

        if height is None:
            scaling_factor = float(width) / float(self.width)
            height = round(self.height * scaling_factor)

        return Emu(width), Emu(height)