def lum_contrast(clip, lum=0, contrast=0, contrast_thr=127):
    """ luminosity-contrast correction of a clip """

    def fl_image(im):
        im = 1.0 * im  # float conversion
        corrected = im + lum + contrast * (im - float(contrast_thr))
        corrected[corrected < 0] = 0
        corrected[corrected > 255] = 255
        return corrected.astype("uint8")

    return clip.fl_image(fl_image)
