RPN网络的smoothL1 loss

RPN网络以及fast rcnn网络的一个bounding-box regression损失函数smoothL1 loss，如下：

TensorFlow实现： 

def smooth_l1_loss(bbox_pred, bbox_targets, bbox_inside_weights, bbox_outside_weights, sigma=1.0, dim=[1]):
    '''
    bbox_pred   ：预测框
    bbox_targets：标签框
    bbox_inside_weights：
    bbox_outside_weights：
    '''  
    sigma_2 = sigma ** 2
    box_diff = bbox_pred - bbox_targets
    in_box_diff = bbox_inside_weights * box_diff
    abs_in_box_diff = tf.abs(in_box_diff)
    # tf.less 返回 True or False； a

 参考

[1] https://blog.csdn.net/u014365862/article/details/79924201