用图拉普拉斯能量优化无训练检测图像异常,通过偏离正常结构程度评分。
Anomaly as Non-Conformity via Training-Free Graph Laplacian Energy Minimization

- 构建查询与正常样本的二分图,仅保留跨类边以避免信息稀释。
- 异常分数为使特征满足正常约束所需的更新量,无需学习参数。
- 方法简洁高效,适合对鲁棒性要求高的工业异常检测场景。
在仅有正常样本的前提下,检测图像中细微的视觉异常仍具挑战性。现有方法通常通过度量查询块与正常块特征相似性来判断异常,但相似性无法揭示其违反正常特征流形结构的程度。本文提出一种无训练的图拉普拉斯能量优化方法 ANoCo,通过计算查询块与固定正常流形之间的非一致性成本来评分异常。对于每个查询块,构建一个基于余弦相似性的二分图,显式移除查询-查询和正常-正常之间的边,防止证据稀释。将异常评分定义为带有锚定正常节点的凸图拉普拉斯能量,并闭式求解。特别地,不使用优化后的特征——异常分数即为满足正常性约束所需更新的幅度,将图拉普拉斯重新视为非一致性算子而非平滑先验。该方法不引入可学习参数、消息传递或采样,复杂度相当于单次线性求解。在多个标准基准上,该方法实现了强图像级 AUROC、稳定定位图,并相比先前方法提升了鲁棒性,证明了利用优化诱导特征漂移作为异常度量的有效性。
原文摘要 · Abstract (English)
Detecting subtle visual anomalies in images remains challenging, particularly when only normal samples are available a priori. Such unsupervised anomaly detection is typically solved by measuring feature similarity of a query patch to a memory of normal patches. However, similarity alone does not reveal how strongly a query patch violates the structure of the normal feature manifold. We propose a training-free Laplacian graph energy optimization formulation, named ANoCo that scores Anomaly by the cost of Non-Conformity of a query patch to align with a fixed normal manifold. For each query patch, we construct a bipartite query to normal graph weighted by cosine affinity, explicitly removing query-query and normal-normal edges to prevent evidence dilution. We formulate anomaly scoring as a convex Laplacian energy with anchored normal nodes, and solve in closed form. In particular, we do not use the optimized features themselves-the anomaly score is the magnitude of the update required to satisfy normality constraints, reframing the graph Laplacian as a non-conformity operator rather than a smoothing prior. The proposed method introduces no learnable parameters, message passing, or sampling, and has complexity comparable to a single linear solve. Across standard benchmarks, it delivers strong image-level AUROC, stable localization maps, and improved robustness over prior methods, demonstrating the effectiveness of using optimization-induced feature drift as anomaly measure.
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