def _native_size(self):
        """
        A (width, height) 2-tuple representing the native dimensions of the
        image in EMU, calculated based on the image DPI value, if present,
        assuming 72 dpi as a default.
        """
        EMU_PER_INCH = 914400
        horz_dpi, vert_dpi = self._dpi
        width_px, height_px = self._px_size

        width = EMU_PER_INCH * width_px / horz_dpi
        height = EMU_PER_INCH * height_px / vert_dpi

        return width, height