Publicacions CVC -- Query Results

Xialei Liu, Joost Van de Weijer, & Andrew Bagdanov. (2019). Exploiting Unlabeled Data in CNNs by Self-Supervised Learning to Rank. TPAMI - IEEE Transactions on Pattern Analysis and Machine Intelligence, 41(8), 1862–1878. Abstract: 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. Keywords: Task analysis;Training;Image quality;Visualization;Uncertainty;Labeling;Neural networks;Learning from rankings;image quality assessment;crowd counting;active learning http://refbase.cvc.uab.es/show.php?record=3267
Xialei Liu, Joost Van de Weijer, & Andrew Bagdanov. (2017). RankIQA: Learning from Rankings for No-reference Image Quality Assessment. In 17th IEEE International Conference on Computer Vision. Abstract: We propose a no-reference image quality assessment (NR-IQA) approach that learns from rankings (RankIQA). To address the problem of limited IQA dataset size, we train a Siamese Network to rank images in terms of image quality by using synthetically generated distortions for which relative image quality is known. These ranked image sets can be automatically generated without laborious human labeling. We then use fine-tuning to transfer the knowledge represented in the trained Siamese Network to a traditional CNN that estimates absolute image quality from single images. We demonstrate how our approach can be made significantly more efficient than traditional Siamese Networks by forward propagating a batch of images through a single network and backpropagating gradients derived from all pairs of images in the batch. Experiments on the TID2013 benchmark show that we improve the state-of-the-art by over 5%. Furthermore, on the LIVE benchmark we show that our approach is superior to existing NR-IQA techniques and that we even outperform the state-of-the-art in full-reference IQA (FR-IQA) methods without having to resort to high-quality reference images to infer IQA. http://refbase.cvc.uab.es/show.php?record=3036
Xialei Liu, Joost Van de Weijer, & Andrew Bagdanov. (2018). Leveraging Unlabeled Data for Crowd Counting by Learning to Rank. In 31st IEEE Conference on Computer Vision and Pattern Recognition (pp. 7661–7669). Abstract: We propose a novel crowd counting approach that leverages abundantly available unlabeled crowd imagery in a learning-to-rank framework. To induce a ranking of cropped images , we use the observation that any sub-image of a crowded scene image is guaranteed to contain the same number or fewer persons than the super-image. This allows us to address the problem of limited size of existing datasets for crowd counting. We collect two crowd scene datasets from Google using keyword searches and queryby-example image retrieval, respectively. We demonstrate how to efficiently learn from these unlabeled datasets by incorporating learning-to-rank in a multi-task network which simultaneously ranks images and estimates crowd density maps. Experiments on two of the most challenging crowd counting datasets show that our approach obtains state-ofthe-art results. Keywords: Task analysis; Training; Computer vision; Visualization; Estimation; Head; Context modeling http://refbase.cvc.uab.es/show.php?record=3159

Xialei Liu, Joost Van de Weijer, & Andrew Bagdanov. (2019). Exploiting Unlabeled Data in CNNs by Self-Supervised Learning to Rank. TPAMI - IEEE Transactions on Pattern Analysis and Machine Intelligence, 41(8), 1862–1878.

Xialei Liu, Joost Van de Weijer, & Andrew Bagdanov. (2017). RankIQA: Learning from Rankings for No-reference Image Quality Assessment. In 17th IEEE International Conference on Computer Vision.

Xialei Liu, Joost Van de Weijer, & Andrew Bagdanov. (2018). Leveraging Unlabeled Data for Crowd Counting by Learning to Rank. In 31st IEEE Conference on Computer Vision and Pattern Recognition (pp. 7661–7669).