def clean_luminance(l_df):
    """ Cleans a luminance dataframe by removing uneeded label field
    Parameters
    ----------
    l_df
        luminance dataframe (8X8 or 28X28) to clean
    Returns
    -------
    pandas.core.frame.DataFrame
        Cleaned luminance dataframe
    """
    l_df.drop(columns='label', inplace=True)
    return(l_df)