How to align several subplot in matplotlib?

Question

I'd like to have four plots with images. All channels, and one for Red, Green and Blue channel. For RGB I'd like to plot a color profile across columns and rows. I would like to have the profile plots aligned exactly to the corresponding image. I mean their width and length should match to width and length, of an image. Their heights should be equal.

For now I achieved this effect using GridSpec. I know I can manipualte by changing fig size proportions, but it is not the solution. I need exact fit.

Here is my code.

    def show_signal_across_image(self):
        fig = plt.figure(figsize=(8, 9), dpi=109)
        gs = GridSpec(4, 4,
                      height_ratios=[10, 2, 10, 2],
                      width_ratios=[10, 2, 10, 2],
                      left=0.05,
                      right=1 - 0.03,
                      top=0.95,
                      bottom=0.06,
                      hspace=0.3,
                      wspace=0.4)
        ax_all = fig.add_subplot(gs[0])
        ax_red_img = fig.add_subplot(gs[2])
        ax_green_img = fig.add_subplot(gs[8])
        ax_blue_img = fig.add_subplot(gs[10])

        ax_red_signal_horizontal = fig.add_subplot(gs[6], sharex=ax_red_img)
        ax_red_signal_vertical = fig.add_subplot(gs[3], sharey=ax_red_img)

        ax_green_signal_horizontal = fig.add_subplot(gs[12], sharex=ax_green_img)
        ax_green_signal_vertical = fig.add_subplot(gs[9], sharey=ax_green_img)

        ax_blue_signal_horizontal = fig.add_subplot(gs[14], sharex=ax_blue_img)
        ax_blue_signal_vertical = fig.add_subplot(gs[11], sharey=ax_blue_img)

        signals = self.get_signal_values()
        red_horizontal, red_vertical, green_horizontal, green_vertical, blue_horizontal, blue_vertical = signals
        horizontal_signals = [red_horizontal, green_horizontal, blue_horizontal]
        vertical_signals = [red_vertical, green_vertical, blue_vertical]
        max_value_horizontal = max([item for sublist in horizontal_signals for item in sublist])
        max_value_vertical = max([item for sublist in vertical_signals for item in sublist])

        ax_red_signal_horizontal.plot(red_horizontal)
        ax_green_signal_horizontal.plot(green_horizontal)
        ax_blue_signal_horizontal.plot(blue_horizontal)

        ax_red_signal_vertical.plot(red_vertical, np.arange(len(red_vertical)))
        ax_green_signal_vertical.plot(green_vertical, np.arange(len(green_vertical)))
        ax_blue_signal_vertical.plot(blue_vertical, np.arange(len(blue_vertical)))

        ax_red_signal_vertical.invert_xaxis()
        ax_green_signal_vertical.invert_xaxis()
        ax_blue_signal_vertical.invert_xaxis()

        for ax in [ax_red_signal_horizontal, ax_green_signal_horizontal, ax_blue_signal_horizontal]:
            ax.set_ylim(0, max_value_horizontal * 1.1)
        for ax in [ax_red_signal_vertical, ax_green_signal_vertical, ax_blue_signal_vertical]:
            ax.set_xlim(max_value_vertical * 1.1, 0)

        imshow_args = dict(vmin=0, vmax=1, cmap='gray')
        plt.subplot(ax_all)
        plt.title('All channels')
        plt.imshow(self.img, **imshow_args)
        plt.subplot(ax_red_img)
        plt.title('Red')
        plt.imshow(self.red, **imshow_args)
        plt.subplot(ax_green_img)
        plt.title('Green')
        plt.imshow(self.green, **imshow_args)
        plt.subplot(ax_blue_img)
        plt.title('Blue')
        plt.imshow(self.blue, **imshow_args)

        plt.show()

I'm using matplotlib 3.1.1 and python 3.7.1.