Normalize src with mean and std.

    Parameters
    ----------
    src : NDArray
        Input image
    mean : NDArray
        RGB mean to be subtracted
    std : NDArray
        RGB standard deviation to be divided

    Returns
    -------
    NDArray
        An `NDArray` containing the normalized image.

def color_normalize(src, mean, std=None):
    """Normalize src with mean and std.

    Parameters
    ----------
    src : NDArray
        Input image
    mean : NDArray
        RGB mean to be subtracted
    std : NDArray
        RGB standard deviation to be divided

    Returns
    -------
    NDArray
        An `NDArray` containing the normalized image.
    """
    if mean is not None:
        src -= mean
    if std is not None:
        src /= std
    return src