The deficiency of segmentation labels is one of the main obstacles to semantic segmentation in the wild. To alleviate this issue, we present a novel framework that generates segmentation labels of images given their image-level class labels. In this weakly supervised setting, trained models have been known to segment local discriminative parts rather than the entire object area. Our solution is to propagate such local responses to nearby areas which belong to the same semantic entity. To this end, we propose a Deep Neural Network (DNN) called AffinityNet that predicts semantic affinity between a pair of adjacent image coordinates. The semantic propagation is then realized by random walk with the affinities predicted by AffinityNet. More importantly, the supervision employed to train AffinityNet is given by the initial discriminative part segmentation, which is incomplete as a segmentation annotation but sufficient for learning semantic affinities within small image areas. Thus the entire framework relies only on image-level class labels and does not require any extra data or annotations. On the PASCAL VOC 2012 dataset, a DNN learned with segmentation labels generated by our method outperforms previous models trained with the same level of supervision, and is even as competitive as those relying on stronger supervision.

本文提出了一种用于弱监督下的图像标注的全新框架——AffinityNet。该框架通过训练一个深度神经网络，使其能够预测一对相邻图像坐标之间的语义亲和性，从而通过随机游走来实现语义的传播，以生成图像的分割标签。实验表明，使用我们的方法生成的分割标签训练的DNN，甚至比其它依赖于更强监管的模型表现更为优秀。

基于图像级别监督学习像素级语义相似性用于弱监督语义分割