def is_image(tensor):
    """
    Check if a tensor has the shape of
    a valid image for tensorboard logging.
    Valid image: RGB, RGBD, GrayScale

    :param tensor: (np.ndarray or tf.placeholder)
    :return: (bool)
    """
    return len(tensor.shape) == 3 and tensor.shape[-1] in [1, 3, 4]
