sixel_dither_unref(
    sixel_dither_t  /* in */ *dither)
{
    /* TODO: be thread safe */
    if (dither != NULL && --dither->ref == 0) {
        sixel_dither_destroy(dither);
    }
}
sixel_dither_unref(
    sixel_dither_t    *dither)
{
     
    if (dither != NULL && --dither->ref == 0) {
        sixel_dither_destroy(dither);
    }
}