import tensorflow as tf

    # size: num_priors
    labels = tf.gather(gt_labels, best_target_per_prior_index)

    labels = tf.where(tf.less(best_target_per_prior, iou_threshold), tf.constant(0, dtype='int64'), labels)

    # labels[best_target_per_prior < iou_threshold] = 0  # the backgournd id
    boxes = tf.gather(gt_boxes, best_target_per_prior_index)
    return boxes, labels

class MatchPrior(object):
    def __init__(self, center_form_priors, center_variance, size_variance, iou_threshold):
        self.center_form_priors = center_form_priors
