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Kekai Sheng

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4 papers

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AAAI Conference 2022 Conference Paper

Evo-ViT: Slow-Fast Token Evolution for Dynamic Vision Transformer

Yifan Xu
Zhijie Zhang
Mengdan Zhang
Kekai Sheng
Ke Li
Weiming Dong
Liqing Zhang
Changsheng Xu

Vision transformers (ViTs) have attracted considerable research attention recently, but the huge computational cost is still a severe issue. A mainstream paradigm for computation reduction aims to reduce the number of tokens given that the computation complexity of ViT is quadratic with respect to the input sequence length. Existing designs include structured spatial compression that uses a progressive shrinking pyramid to reduce the computations of large feature maps, and unstructured token pruning that dynamically drops redundant tokens. However, limitations of existing token pruning lie in the following aspects: 1) the incomplete spatial structure caused by pruning is incompatible with structured spatial compression that is commonly used in modern deep-narrow transformers; 2) it usually requires a time-consuming pretraining procedure. To address the limitations and expand the applicable scenario of token pruning, we present Evo-ViT, a self-motivated slow-fast token evolution approach for vision transformers. Specifically, we conduct unstructured instancewise token selection by taking advantage of the simple and effective global class attention that is native to vision transformers. Then, we propose to update the selected informative tokens and uninformative tokens with different computation paths, namely, slow-fast updating. Since slow-fast updating mechanism maintains the spatial structure and information flow, Evo-ViT can accelerate vanilla transformers of both flat and deep-narrow structures from the very beginning of the training process. Experimental results demonstrated that our method significantly reduces the computational cost of vision transformers while maintaining comparable performance on image classification. For example, our method accelerates DeiT-S by over 60% throughput while only sacrificing 0. 4% top-1 accuracy on ImageNet-1K, outperforming current token pruning methods on both accuracy and efficiency.

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IJCAI Conference 2021 Conference Paper

Dual Reweighting Domain Generalization for Face Presentation Attack Detection

Shubao Liu
Ke-Yue Zhang
Taiping Yao
Kekai Sheng
Shouhong Ding
Ying Tai
Jilin Li
Yuan Xie

Face anti-spoofing approaches based on domain generalization (DG) have drawn growing attention due to their robustness for unseen scenarios. Previous methods treat each sample from multiple domains indiscriminately during the training process, and endeavor to extract a common feature space to improve the generalization. However, due to complex and biased data distribution, directly treating them equally will corrupt the generalization ability. To settle the issue, we propose a novel Dual Reweighting Domain Generalization (DRDG) framework which iteratively reweights the relative importance between samples to further improve the generalization. Concretely, Sample Reweighting Module is first proposed to identify samples with relatively large domain bias, and reduce their impact on the overall optimization. Afterwards, Feature Reweighting Module is introduced to focus on these samples and extract more domain-irrelevant features via a self-distilling mechanism. Combined with the domain discriminator, the iteration of the two modules promotes the extraction of generalized features. Extensive experiments and visualizations are presented to demonstrate the effectiveness and interpretability of our method against the state-of-the-art competitors.

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AAAI Conference 2021 Conference Paper

Generalizable Representation Learning for Mixture Domain Face Anti-Spoofing

Zhihong Chen
Taiping Yao
Kekai Sheng
Shouhong Ding
Ying Tai
Jilin Li
Feiyue Huang
Xinyu Jin

Face anti-spoofing approach based on domain generalization (DG) has drawn growing attention due to its robustness for unseen scenarios. Existing DG methods assume that the domain label is known. However, in real-world applications, the collected dataset always contains mixture domains, where the domain label is unknown. In this case, most of existing methods may not work. Further, even if we can obtain the domain label as existing methods, we think this is just a sub-optimal partition. To overcome the limitation, we propose domain dynamic adjustment meta-learning (D2 AM) without using domain labels, which iteratively divides mixture domains via discriminative domain representation and trains a generalizable face anti-spoofing with meta-learning. Specifically, we design a domain feature based on Instance Normalization (IN) and propose a domain representation learning module (DRLM) to extract discriminative domain features for clustering. Moreover, to reduce the side effect of outliers on clustering performance, we additionally utilize maximum mean discrepancy (MMD) to align the distribution of sample features to a prior distribution, which improves the reliability of clustering. Extensive experiments show that the proposed method outperforms conventional DG-based face anti-spoofing methods, including those utilizing domain labels. Furthermore, we enhance the interpretability through visualization.

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AAAI Conference 2020 Conference Paper

Revisiting Image Aesthetic Assessment via Self-Supervised Feature Learning

Kekai Sheng
Weiming Dong
Menglei Chai
Guohui Wang
Peng Zhou
Feiyue Huang
Bao-Gang Hu
Rongrong Ji

Visual aesthetic assessment has been an active research ﬁeld for decades. Although latest methods have achieved promising performance on benchmark datasets, they typically rely on a large number of manual annotations including both aesthetic labels and related image attributes. In this paper, we revisit the problem of image aesthetic assessment from the selfsupervised feature learning perspective. Our motivation is that a suitable feature representation for image aesthetic assessment should be able to distinguish different expertdesigned image manipulations, which have close relationships with negative aesthetic effects. To this end, we design two novel pretext tasks to identify the types and parameters of editing operations applied to synthetic instances. The features from our pretext tasks are then adapted for a one-layer linear classiﬁer to evaluate the performance in terms of binary aesthetic classiﬁcation. We conduct extensive quantitative experiments on three benchmark datasets and demonstrate that our approach can faithfully extract aesthetics-aware features and outperform alternative pretext schemes. Moreover, we achieve comparable results to state-of-the-art supervised methods that use 10 million labels from ImageNet.

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