def sc_zoom_coarse(self, viewer, event, msg=True):
        """Interactively zoom the image by scrolling motion.
        This zooms by adjusting the scale in x and y coarsely.
        """
        if not self.canzoom:
            return True

        zoom_accel = self.settings.get('scroll_zoom_acceleration', 1.0)
        # change scale by 20%
        amount = self._scale_adjust(1.2, event.amount, zoom_accel, max_limit=4.0)
        self._scale_image(viewer, event.direction, amount, msg=msg)
        return True
Interactively zoom the image by scrolling motion.
        This zooms by adjusting the scale in x and y coarsely.