Updates image to be displayed with new time frame.

def update(self):
        """Updates image to be displayed with new time frame."""
        if self.single_channel:
            self.im.set_data(self.data[self.ind, :, :])
        else:
            self.im.set_data(self.data[self.ind, :, :, :])
        self.ax.set_ylabel('time frame %s' % self.ind)
        self.im.axes.figure.canvas.draw()