def add_FDI(data):
    """
    Forest Discrimination Index (FDI) = (NIR - (Red + Blue)), for 6 bands images, (FDI) = (B8 - (B6 + B2)), for 8 bands images
    """
    return ((data[7,:,:] - (data[5,:,:] + data[1,:,:]))).expand_dims(dim="band", axis=0)