Recommender system (RS) aims to capture personalized preferences from massive user behaviors, making them pivotal in the era of information explosion. However, the presence of “information cocoons,” interaction sparsity, cold-start problem, and feedback loops inherent in RS make users interact with a limited number of items. Conventional recommendation algorithms typically focus on the positive historical behaviors, while neglecting the essential role of negative feedback in user preference understanding. As a promising but easy-to-ignored area, negative sampling is proficient in revealing the genuine negative aspect inherent in user behaviors, emerging as an inescapable procedure in RS. In this survey, we first discuss existing user feedback, the critical role of negative sampling and the optimization objectives in RS, and thoroughly analyze challenges that consistently impede its progress. Then, we conduct an extensive literature review on the existing negative sampling strategies in RS and classify them into five categories with their discrepant techniques. Finally, we detail the insights of the tailored negative sampling strategies in diverse RS scenarios and outline an overview of the prospective research directions toward which the community may engage and benefit.

Deep learning has been proven to be effective in image classification tasks. However, existing methods may face difficulties in distinguishing complex images due to the distraction caused by diverse image content. To overcome this challenge, we propose a class-aware convolution and attentive aggregation (CA-Net) framework that improves the effectiveness of representation learning and reduces the influence of irrelevant background. CA-Net includes three main modules: the discrete representation learning (DRL) module that uses a group learning method to learn discriminative representations, the class-aware score of discrete representation (CSDR) module that infers class-aware scores to generate weights for representation learners, and the class-aware representation fusion module(CRF) that aggregates class-aware representations using the class-aware scores as a guide. Our experimental results on three benchmarking datasets show that CA-Net improves the performance of state-of-the-art backbones and enhances feature extraction robustness.

In this paper, we focus on generating photo-realistic images from given text descriptions. Current methods first generate an initial image and then progressively refine it to a high-resolution one. These methods typically indiscriminately refine all granularity features output from the previous stage. However, the ability to express different granularity features in each stage is not consistent, and it is difficult to express precise semantics by further refining the features with poor quality generated in the previous stage. Current methods cannot refine different granularity features independently, resulting in that it is challenging to clearly express all factors of semantics in generated image, and some features even become worse. To address this issue, we propose a Hierarchical Disentangled Representations Generative Adversarial Networks (HDR-GAN) to generate photo-realistic images by explicitly disentangling and individually modeling the factors of semantics in the image. HDR-GAN introduces a novel component called multi-granularity feature disentangled encoder to represent image information comprehensively through explicitly disentangling multi-granularity features including pose, shape and texture. Moreover, we develop a novel Multi-granularity Feature Refinement (MFR) containing a Coarse-grained Feature Refinement (CFR) model and a Fine-grained Feature Refinement (FFR) model. CFR utilizes coarse-grained disentangled representations (e.g., pose and shape) to clarify category information, while FFR employs fine-grained disentangled representations (e.g., texture) to reflect instance-level details. Extensive experiments on two well-studied and publicly available datasets (i.e., CUB-200 and CLEVR-SV) demonstrate the rationality and superiority of our method.

Haze classification has gained much attention recently as a cost-effective solution for air quality monitoring. Different from conventional image classification tasks, it requires the classifier to capture the haze patterns of different severity degrees. Existing efforts typically focus on the extraction of effective haze features, such as the dark channel and deep features. However, it is observed that the light-haze images are often mis-classified due to the presence of diverse background scenes. To address this issue, this paper presents an unsupervised contrastive masking (UCM) algorithm to segment the haze regions without any supervision, and develops a dual-channel model-agnostic framework, termed magnifier neural network (MagNet), to effectively use the segmented haze regions to enhance the learning of haze features by conventional deep learning models. Specifically, MagNet employs the haze regions to provide the pixel- and feature-level visual information via three strategies, including Input Augmentation, Network Constraint, and Feature Enhancement, which work as a soft-attention regularizer to alleviates the trade-off between capturing the global scene information and the local information in the haze regions. Experiments were conducted on two datasets in terms of performance comparison, parameter estimation, ablation studies, and case studies, and the results verified that UCM can accurately and rapidly segment the haze regions, and the proposed three strategies of MagNet consistently improve the performance of the state-of-the-art deep learning backbones.

Traditional Chinese painting is a unique form of artistic expression. Compared with western art painting, it pays more attention to the verve in visual effect, especially ink painting, which makes good use of lines and pays little attention to information such as texture. Some style transfer methods have recently begun to apply traditional Chinese painting style (such as ink wash style) to photorealistic. Ink stylization of different types of real-world photos in a dataset using these style transfer methods has some limitations. When the input images are animal types that have not been seen in the training set, the generated results retain some semantic features of the data in the training set, resulting in distortion. Therefore, in this paper, we attempt to separate the feature representations for styles and contents and propose a style-woven attention network to achieve zero-shot ink wash painting style transfer. Our model learns to disentangle the data representations in an unsupervised fashion and capture the semantic correlations of content and style. In addition, an ink style loss is added to improve the learning ability of the style encoder. In order to verify the ability of ink wash stylization, we augmented the publicly available dataset $ChipPhi$. Extensive experiments based on a wide validation set prove that our method achieves state-of-the-art results.

The automatic generation of Chinese fonts is challenging due to the large quantity and complex structure of Chinese characters. When there are insufficient reference samples for the target font, existing deep learning-based methods cannot avoid overfitting caused by too few samples, resulting in blurred glyphs and incomplete strokes. To address these problems, this paper proposes a novel deep meta-learning-based font generation method (MLFont) for few-shot Chinese font generation, which leverages existing fonts to improve the generalization capability of the model for new fonts. Existing deep meta-learning methods mainly focus on few-shot image classification. To apply meta-learning to font generation, we present a meta-training strategy based on Model-Agnostic Meta-Learning (MAML) and a task organization method for font generation. The meta-training makes the font generator easy to fine-tune for new font generation tasks. Through random font generation tasks and extraction of glyph content and style separately, the font generator learns the prior knowledge of character structure in the meta-training stage, and then quickly adapts to the generation of new fonts with a few samples by fine-tuning of adversarial training. Extensive experiments demonstrate that our method outperforms the state-of-the-art methods with more complete strokes and less noise in the generated character images.