def __init__(self, opt: Opt, shared: PT.TShared = None):
        self.blank_image_id = '0000'
        super().__init__(opt, shared)
        if shared is not None:
            self.valid_image_ids = shared['valid_image_ids']
        if self.image_features_dict is not None:
            self.image_features_dict[self.blank_image_id] = self.blank_image_features
        self.multi_ref = opt.get('igc_multi_ref', False)