def blend(img_under, img_over, img_alpha):
    """
    Blend together two images using an alpha channel image

    Parameters:

    - img_under -- The base image (underneath the overlay)
    - img_over  -- The overlay image
    - img_alpha -- Transparency/alpha value to use when blending
    """
    return img_under * (1 - img_alpha[:, :, (None)]) + img_over * img_alpha[:,
        :, (None)]
