def _format_spectrogram(ax, qspecgram, colormap='viridis'):
    """Helper tool to format a `~gwpy.spectrogram.Spectrogram` plot axis
    """
    ax.imshow(qspecgram)
    ax.colorbar(cmap=colormap, norm='linear', clim=(0, 25), label=
        'Normalized energy')
    ax.set_yscale('linear')
    ax.set_ylabel('Frequency [Hz]')
    ax.grid(True, axis='y', which='both')
