PT Journal
AU Xialei Liu
   Joost Van de Weijer
   Andrew Bagdanov
TI Exploiting Unlabeled Data in CNNs by Self-Supervised Learning to Rank
SO IEEE Transactions on Pattern Analysis and Machine Intelligence
JI TPAMI
PY 2019
BP 1862
EP 1878
VL 41
IS 8
DI 10.1109/TPAMI.2019.2899857
DE Task analysis; Training; Image quality; Visualization; Uncertainty; Labeling; Neural networks; Learning from rankings; image quality assessment; crowd counting; active learning
AB For many applications the collection of labeled data is expensive laborious. Exploitation of unlabeled data during training is thus a long pursued objective of machine learning. Self-supervised learning addresses this by positing an auxiliary task (different, but related to the supervised task) for which data is abundantly available. In this paper, we show how ranking can be used as a proxy task for some regression problems. As another contribution, we propose an efficient backpropagation technique for Siamese networks which prevents the redundant computation introduced by the multi-branch network architecture. We apply our framework to two regression problems: Image Quality Assessment (IQA) and Crowd Counting. For both we show how to automatically generate ranked image sets from unlabeled data. Our results show that networks trained to regress to the ground truth targets for labeled data and to simultaneously learn to rank unlabeled data obtain significantly better, state-of-the-art results for both IQA and crowd counting. In addition, we show that measuring network uncertainty on the self-supervised proxy task is a good measure of informativeness of unlabeled data. This can be used to drive an algorithm for active learning and we show that this reduces labeling effort by up to 50 percent.
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