PromptAD: Learning Prompts with only Normal Samples for Few-Shot Anomaly Detection
Authors: Xiaofan Li, Zhizhong Zhang, Xin Tan, Chengwei Chen, Yanyun Qu, Yuan Xie, Lizhuang Ma

The vision-language model has brought great improvement to few-shot industrial anomaly detection which usually needs to design of hundreds of prompts through prompt engineering. For automated scenarios we first use conventional prompt learning with many-class paradigm as the baseline to automatically learn prompts but found that it can not work well in one-class anomaly detection. To address the above problem this paper proposes a one-class prompt learning method for few-shot anomaly detection termed PromptAD. First we propose semantic concatenation which can transpose normal prompts into anomaly prompts by concatenating normal prompts with anomaly suffixes thus constructing a large number of negative samples used to guide prompt learning in one-class setting. Furthermore to mitigate the training challenge caused by the absence of anomaly images we introduce the concept of explicit anomaly margin which is used to explicitly control the margin between normal prompt features and anomaly prompt features through a hyper-parameter. For image-level/pixel-level anomaly detection PromptAD achieves first place in 11/12 few-shot settings on MVTec and VisA.