Prototype Completion with Primitive Knowledge for Few-Shot Learning

by   Baoquan Zhang, et al.

Few-shot learning is a challenging task, which aims to learn a classifier for novel classes with few labeled samples. Previous studies mainly focus on two-phase meta-learning methods. Recently, researchers find that introducing an extra pre-training phase can significantly improve the performance. The key idea is to learn a feature extractor with pre-training and then fine-tune it through the nearest centroid based meta-learning. However, results show that the fine-tuning step makes very marginal improvements. We thus argue that the current meta-learning scheme does not fully explore the power of the pre-training. The reason roots in the fact that in the pre-trained feature space, the base classes already form compact clusters while novel classes spread as groups with large variances. In this case, fine-tuning the feature extractor is less meaningful than estimating more representative prototypes. However, making such an estimation from few labeled samples is challenging because they may miss representative attribute features. In this paper, we propose a novel prototype completion based meta-learning framework. The framework first introduces primitive knowledge (i.e., class-level attribute or part annotations) and extracts representative attribute features as priors. A prototype completion network is then designed to learn to complement the missing attribute features with the priors. Finally, we develop a Gaussian based prototype fusion strategy to combine the mean-based and the complemented prototypes, which can effectively exploit the unlabeled samples. Extensive experimental results on three real-world data sets demonstrate that our method: (i) can obtain more accurate prototypes; (ii) outperforms state-of-the-art techniques by 2


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