Harnessing Vision-Language Models for Time Series Anomaly Detection

TL;DR

This paper introduces a novel two-stage approach utilizing vision-language models for time series anomaly detection, significantly improving accuracy and efficiency without requiring time-series training.

Contribution

It presents a new method combining lightweight vision encoders and VLMs for anomaly detection, outperforming existing models without additional training.

Findings

VLM4TS outperforms baselines with 24.6% higher F1-max score.

The approach is 36x more efficient in token usage.

It achieves superior accuracy without time-series training.

Abstract

Time-series anomaly detection (TSAD) has played a vital role in a variety of fields, including healthcare, finance, and sensor-based condition monitoring. Prior methods, which mainly focus on training domain-specific models on numerical data, lack the visual-temporal understanding capacity that human experts have to identify contextual anomalies. To fill this gap, we explore a solution based on vision language models (VLMs). Recent studies have shown the ability of VLMs for visual understanding tasks, yet their direct application to time series has fallen short on both accuracy and efficiency. To harness the power of VLMs for TSAD, we propose a two-stage solution, with (1) ViT4TS, a vision-screening stage built on a relatively lightweight pre-trained vision encoder, which leverages 2D time series representations to accurately localize candidate anomalies; (2) VLM4TS, a VLM-based stage that integrates global temporal context and VLM's visual understanding capacity to refine the detection upon the candidates provided by ViT4TS. We show that without any time-series training, VLM4TS outperforms time-series pre-trained and from-scratch baselines in most cases, yielding a 24.6% improvement in F1-max score over the best baseline. Moreover, VLM4TS also consistently outperforms existing language model-based TSAD methods and is on average 36x more efficient in token usage.