on release we reset the press data

def on_release(self, event):
        'on release we reset the press data'
        if self.press is None:
            return
        # print(self.press)
        x0, y0, btn = self.press
        if btn == 1:
            color = 'r'
        elif btn == 2:
            color = 'b'  # noqa

        # plt.axes(self.ax)
        # plt.plot(x0, y0)
        # button Mapping
        btn = self.button_map[btn]

        self.set_seeds(y0, x0, self.actual_slice, btn)
        # self.fig.canvas.draw()
        # pdb.set_trace();
        self.press = None
        self.update_slice()