A Closer Look at Few-Shot Classification with Many Novel Classes

Revisiting metric learning for few-shot image classification

Coarse-to-fine pseudo supervision guided meta-task optimization for few-shot object classification

Self-supervised learning (SSL) techniques have recently been integrated into the few-shot learning (FSL) framework and have shown promising results in improving the few-shot image classification performance. However, existing SSL approaches used in FSL typically seek the supervision signals from the global embedding of every single image. Therefore, during the episodic training of FSL, these methods cannot capture and fully utilize the local visual information in image samples and the data structure information of the whole episode, which are beneficial to FSL. To this end, we propose to augment the few-shot learning objective with a novel self-supervised Episodic Spatial Pretext Task (ESPT). Specifically, for each few-shot episode, we generate its corresponding transformed episode by applying a random geometric transformation to all the images in it. Based on these, our ESPT objective is defined as maximizing the local spatial relationship consistency between the original episode and the transformed one. With this definition, the ESPT-augmented FSL objective promotes learning more transferable feature representations that capture the local spatial features of different images and their inter-relational structural information in each input episode, thus enabling the model to generalize better to new categories with only a few samples. Extensive experiments indicate that our ESPT method achieves new state-of-the-art performance for few-shot image classification on three mainstay benchmark datasets. The source code will be available at: https://github.com/Whut-YiRong/ESPT.

Few-shot learning aims to learn a classifier to recognize unseen classes with limited labeled examples. The scarcity of training data remains a challenging problem in few-shot classification. Many few-shot learning methods focus on the structure of meta-network models and there is often no dedicated study of meta-knowledge representation. In this paper, a meta-learning strategy is introduced and a meta-network NAM Net is proposed. Taking the advantage of 'learning to learn', the model acquires meta-knowledge via few-shot classification tasks and applies it to new few-shot scenarios. Specifically, the meta-learner learns the best parameters of the feature extraction and similarity metric modules. The distance between the support feature and query feature is obtained by a learnable metric function, which leads to the classification result. The base learner migrates the meta-knowledge to the target class to perform classification in a new few-shot episode. Moreover, the Normalization-based Attention Module is adapted to feature extractor to enhance meta-knowledge representation. Compared with few-shot learning benchmarks, NAM Net is effective and achieves higher accuracy in both 5-way 1-shot and 5-shot classification tasks.

Few-shot learning(FSL) aims to generalize model to novel categoeries by few labelled samples, which is challenging for machine. Large-scaled pretrained models, especially vision transformers achieve excellent performances benefiting from numerous and diverse data. Researchers have exploited pretrained models in few-shot classification by simply updating the whole parameters and finetuning on few samples. In this paper, we explore two methods: vision prompt tuning and a reparameterization method called ‘scaling&&shift’ to leverage pretrained models in few-shot classification. Vision prompt tuning is for vision transformer only and we first evaluate the method in few-shot setting. ‘Scaling&&shift’ is originally applied in convolution neural networks(CNN). We extend it to vision transformer. The two methods are evaluated on standard benchmarks such as miniImageNet, CUB, CIFAR-FS, clipart and sketch. The results show that ‘scaling&&shift’ reaches the same level compared to updating the whole parameters. Vision prompt tuning is 0%~5% lower than updating the whole parameters over five datasets while it has quite smaller amount of parameters updated.

TST_MFL: Two-stage training based metric fusion learning for few-shot image classification

In this paper, we investigate the feasibility of applying few-shot learning algorithms to a speech task. We formulate a user-defined scenario of spoken term classification as a few-shot learning problem. In most few-shot learning studies, it is assumed that all the N classes are new in a N-way problem. We suggest that this assumption can be relaxed and define a N+M-way problem where N and M are the number of new classes and fixed classes respectively. We propose a modification to the Model-Agnostic Meta-Learning (MAML) algorithm to solve the problem. Experiments on the Google Speech Commands dataset show that our approach outperforms the conventional supervised learning approach and the original MAML.

Due to a lack of labeled samples, deep learning methods generally tend to have poor classification performance in practical applications. Few-shot learning (FSL), as an emerging learning paradigm, has been widely utilized in hyperspectral image (HSI) classification with limited labeled samples. However, the existing FSL methods generally ignore the domain shift problem in cross-domain scenes and rarely explore the associations between samples in the source and target domain. To tackle the above issues, a graph-based domain adaptation FSL (GDAFSL) method is proposed for HSI classification with limited training samples, which utilizes the graph method to guide the domain adaptation learning process in a uniformed framework. First, a novel deep residual hybrid attention network (DRHAN) is designed to extract discriminative embedded features efficiently for few-shot HSI classification. Then, a graph-based domain adaptation network (GDAN), which combines graph construction with domain adversarial strategy, is proposed to fully explore the domain correlation between source and target embedded features. By utilizing the fully explored domain correlations to guide the domain adaptation process, a domain invariant feature metric space is learned for few-shot HSI classification. Comprehensive experimental results conducted on three public HSI datasets demonstrate that GDAFSL is superior to the state-of-the-art with a small sample size.

Few-shot learning (FSL) is promising in the field of medical image analysis due to high cost of establishing high-quality medical datasets. Many FSL approaches have been proposed in natural image scenes. However, present FSL methods are rarely evaluated on medical images and the FSL technology applicable to medical scenarios need to be further developed. Meta-learning has supplied an optional framework to address the challenging FSL setting. In this paper, we propose a novel multi-learner based FSL method for multiple medical image classification tasks, combining meta-learning with transfer-learning and metric-learning. Our designed model is composed of three learners, including auto-encoder, metric-learner and task-learner. In transfer-learning, all the learners are trained on the base classes. In the ensuing meta-learning, we leverage multiple novel tasks to fine-tune the metric-learner and task-learner in order to fast adapt to unseen tasks. Moreover, to further boost the learning efficiency of our model, we devised real-time data augmentation and dynamic Gaussian disturbance soft label (GDSL) scheme as effective generalization strategies of few-shot classification tasks. We have conducted experiments for three-class few-shot classification tasks on three newly-built challenging medical benchmarks, BLOOD, PATH and CHEST. Extensive comparisons to related works validated that our method achieved top performance both on homogeneous medical datasets and cross-domain datasets.

Few-shot learning aims to learn a classifier that classifies unseen classes well with limited labeled samples. Existing meta learning-based works, whether graph neural network or other baseline approaches in few-shot learning, has benefited from the meta-learning process with episodic tasks to enhance the generalization ability. However, the performance of meta-learning is greatly affected by the initial embedding network, due to the limited number of samples. In this paper, we propose a novel Multi-granularity Recurrent Attention Graph Neural Network (MRA-GNN), which employs Multi-granularity graph to achieve better generalization ability for few-shot learning. We first construct the Local Proposal Network (LPN) based on attention to generate local images from foreground images. The intra-cluster similarity and the inter-cluster dissimilarity are considered in the local images to generate discriminative features. Finally, we take the local images and original images as the input of multi-grained GNN models to perform classification. We evaluate our work by extensive comparisons with previous GNN approaches and other baseline methods on two benchmark datasets (i.e., miniImageNet and CUB). The experimental study on both of the supervised and semi-supervised few-shot image classification tasks demonstrates the proposed MRA-GNN significantly improves the performances and achieves the state-of-the-art results we know.

GOL-SFSTS based few-shot learning mechanical anomaly detection using multi-channel audio signal

Few-shot learning (FSL) approaches, mostly neural network-based, assume that pre-trained knowledge can be obtained from base (seen) classes and transferred to novel (unseen) classes. However, the black-box nature of neural networks makes it difficult to understand what is actually transferred, which may hamper FSL application in some risk-sensitive areas. In this paper, we reveal a new way to perform FSL for image classification, using a visual representation from the backbone model and patterns generated by a self-attention based explainable module. The representation weighted by patterns only includes a minimum number of distinguishable features and the visualized patterns can serve as an informative hint on the transferred knowledge. On three mainstream datasets, experimental results prove that the proposed method can enable satisfying explainability and achieve high classification results. Code is available at https://github.com/wbw520/MTUNet.

MetAdapt: Meta-learned task-adaptive architecture for few-shot classification

Few-shot classification aims to generalize the concept from seen classes to unseen novel classes using only a few examples. Although significant progress in few-shot classification has been made, most approaches focus on a standard multi-class scenario and are based on learning single-label embedding of the labeled examples to classify the unlabeled examples. Besides, we note that state-of-the-art methods in few-shot learning mostly adopt a metric-based architecture and the the so-called episode training strategy. While this approach works nicely for multiclass classification, it is hard to apply it to the multi-label scenario because of the complexity of forming an episode. In this paper, we propose a One-vs.-Rest episode selection strategy to mitigate this issue and apply the strategy to the multi-label few-shot problem. Experiments conducted using the large-scale data found in the AudioSet show that the models with our training strategy extract the semantic features under the multi-label setting.

The goal of few-shot image classification is to learn a classifier that can be well generalized to the unseen classes with a few available labeled samples. One major challenge for few-shot learning is how to conduct effective image representation for support and query images. Recently, local region-based image representation and metric learning approaches have been demonstrated effectively for few-shot classification problem. However, existing approaches generally conduct representations of image regions individually which thus lack of considering the rich spatial/structural relationships among image regions. In this paper, we propose to bridge the individual regions and exploit the structural contexts among regions via a novel Region-Graph Transformer (RGTransformer). In RGTransformer, each region aggregates the information from its neighboring regions and thus can obtain context-aware feature representations for regions. Using the proposed RGTransformer, we propose an effective metric learning model for few-shot image classification. We evaluate the proposed method on four benchmark datasets and experimental results demonstrate the effectiveness and advantages of the proposed RGTransformer.