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Unsupervisedly detecting anomaly points in time series is challenging, which requires the model to learn informative representations and derive a distinguishable criterion. Prior methods mainly detect anomalies based on the recurrent network representation of each time point. However, the point-wise representation is less informative for complex temporal patterns and can be dominated by normal patterns, making rare anomalies less distinguishable. We find that in each time series, each time point can also be described by its associations with all time points, presenting as a point-wise distribution that is more expressive for temporal modeling. We further observe that due to the rarity of anomalies, it is harder for anomalies to build strong associations with the whole series and their associations shall mainly concentrate on the adjacent time points. This observation implies an inherently distinguishable criterion between normal and abnormal points, which we highlight as the \emph{Association Discrepancy}. Technically we propose the \emph{Anomaly Transformer} with an \emph{Anomaly-Attention} mechanism to compute the association discrepancy. A minimax strategy is devised to amplify the normal-abnormal distinguishability of the association discrepancy. Anomaly Transformer achieves state-of-the-art performance on six unsupervised time series anomaly detection benchmarks for three applications: service monitoring, space \& earth exploration, and water treatment.

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在數(shu)據(ju)挖掘中,異(yi)(yi)常(chang)(chang)檢(jian)測(ce)(英語:anomaly detection)對(dui)不(bu)符合預期模(mo)(mo)(mo)式(shi)或數(shu)據(ju)集(ji)中其(qi)他項目(mu)的(de)(de)(de)(de)項目(mu)、事件或觀測(ce)值(zhi)的(de)(de)(de)(de)識別。通(tong)常(chang)(chang)異(yi)(yi)常(chang)(chang)項目(mu)會轉變成(cheng)銀行(xing)欺詐(zha)、結構缺陷、醫(yi)療(liao)問(wen)題(ti)、文本錯誤(wu)等類型的(de)(de)(de)(de)問(wen)題(ti)。異(yi)(yi)常(chang)(chang)也被(bei)(bei)稱為離群值(zhi)、新(xin)奇(qi)、噪(zao)聲、偏差和例外。 特別是在檢(jian)測(ce)濫(lan)用(yong)與網絡入侵時,有(you)趣性(xing)對(dui)象(xiang)往往不(bu)是罕見對(dui)象(xiang),但卻是超(chao)出(chu)(chu)(chu)預料的(de)(de)(de)(de)突發(fa)活動。這種模(mo)(mo)(mo)式(shi)不(bu)遵循通(tong)常(chang)(chang)統計定(ding)義中把異(yi)(yi)常(chang)(chang)點看作(zuo)是罕見對(dui)象(xiang),于是許多(duo)(duo)異(yi)(yi)常(chang)(chang)檢(jian)測(ce)方法(fa)(fa)(fa)(特別是無(wu)監(jian)督的(de)(de)(de)(de)方法(fa)(fa)(fa))將對(dui)此類數(shu)據(ju)失效,除(chu)非(fei)進行(xing)了合適的(de)(de)(de)(de)聚(ju)(ju)(ju)集(ji)。相反(fan),聚(ju)(ju)(ju)類分析(xi)算法(fa)(fa)(fa)可(ke)能(neng)可(ke)以檢(jian)測(ce)出(chu)(chu)(chu)這些(xie)模(mo)(mo)(mo)式(shi)形成(cheng)的(de)(de)(de)(de)微(wei)聚(ju)(ju)(ju)類。 有(you)三大(da)類異(yi)(yi)常(chang)(chang)檢(jian)測(ce)方法(fa)(fa)(fa)。[1] 在假設數(shu)據(ju)集(ji)中大(da)多(duo)(duo)數(shu)實(shi)例都是正常(chang)(chang)的(de)(de)(de)(de)前提(ti)下(xia),無(wu)監(jian)督異(yi)(yi)常(chang)(chang)檢(jian)測(ce)方法(fa)(fa)(fa)能(neng)通(tong)過尋找與其(qi)他數(shu)據(ju)最不(bu)匹配的(de)(de)(de)(de)實(shi)例來檢(jian)測(ce)出(chu)(chu)(chu)未標(biao)記(ji)測(ce)試(shi)數(shu)據(ju)的(de)(de)(de)(de)異(yi)(yi)常(chang)(chang)。監(jian)督式(shi)異(yi)(yi)常(chang)(chang)檢(jian)測(ce)方法(fa)(fa)(fa)需要一個(ge)已經被(bei)(bei)標(biao)記(ji)“正常(chang)(chang)”與“異(yi)(yi)常(chang)(chang)”的(de)(de)(de)(de)數(shu)據(ju)集(ji),并(bing)涉(she)及到(dao)訓(xun)練(lian)分類器(與許多(duo)(duo)其(qi)他的(de)(de)(de)(de)統計分類問(wen)題(ti)的(de)(de)(de)(de)關鍵區別是異(yi)(yi)常(chang)(chang)檢(jian)測(ce)的(de)(de)(de)(de)內在不(bu)均衡性(xing))。半監(jian)督式(shi)異(yi)(yi)常(chang)(chang)檢(jian)測(ce)方法(fa)(fa)(fa)根(gen)據(ju)一個(ge)給定(ding)的(de)(de)(de)(de)正常(chang)(chang)訓(xun)練(lian)數(shu)據(ju)集(ji)創建一個(ge)表示正常(chang)(chang)行(xing)為的(de)(de)(de)(de)模(mo)(mo)(mo)型,然后(hou)檢(jian)測(ce)由學習模(mo)(mo)(mo)型生(sheng)成(cheng)的(de)(de)(de)(de)測(ce)試(shi)實(shi)例的(de)(de)(de)(de)可(ke)能(neng)性(xing)。

Analyzing sequence data usually leads to the discovery of interesting patterns and then anomaly detection. In recent years, numerous frameworks and methods have been proposed to discover interesting patterns in sequence data as well as detect anomalous behavior. However, existing algorithms mainly focus on frequency-driven analytic, and they are challenging to be applied in real-world settings. In this work, we present a new anomaly detection framework called DUOS that enables Discovery of Utility-aware Outlier Sequential rules from a set of sequences. In this pattern-based anomaly detection algorithm, we incorporate both the anomalousness and utility of a group, and then introduce the concept of utility-aware outlier sequential rule (UOSR). We show that this is a more meaningful way for detecting anomalies. Besides, we propose some efficient pruning strategies w.r.t. upper bounds for mining UOSR, as well as the outlier detection. An extensive experimental study conducted on several real-world datasets shows that the proposed DUOS algorithm has a better effectiveness and efficiency. Finally, DUOS outperforms the baseline algorithm and has a suitable scalability.

The past few years have witnessed an increasing interest in improving the perception performance of LiDARs on autonomous vehicles. While most of the existing works focus on developing new deep learning algorithms or model architectures, we study the problem from the physical design perspective, i.e., how different placements of multiple LiDARs influence the learning-based perception. To this end, we introduce an easy-to-compute information-theoretic surrogate metric to quantitatively and fast evaluate LiDAR placement for 3D detection of different types of objects. We also present a new data collection, detection model training and evaluation framework in the realistic CARLA simulator to evaluate disparate multi-LiDAR configurations. Using several prevalent placements inspired by the designs of self-driving companies, we show the correlation between our surrogate metric and object detection performance of different representative algorithms on KITTI through extensive experiments, validating the effectiveness of our LiDAR placement evaluation approach. Our results show that sensor placement is non-negligible in 3D point cloud-based object detection, which will contribute to 5% ~ 10% performance discrepancy in terms of average precision in challenging 3D object detection settings. We believe that this is one of the first studies to quantitatively investigate the influence of LiDAR placement on perception performance.

Temporal Activity Detection aims to predict activity classes per frame, in contrast to video-level predictions as done in Activity Classification (i.e., Activity Recognition). Due to the expensive frame-level annotations required for detection, the scale of detection datasets is limited. Thus, commonly, previous work on temporal activity detection resorts to fine-tuning a classification model pretrained on large-scale classification datasets (e.g., Kinetics-400). However, such pretrained models are not ideal for downstream detection performance due to the disparity between the pretraining and the downstream fine-tuning tasks. This work proposes a novel self-supervised pretraining method for detection leveraging classification labels to mitigate such disparity by introducing frame-level pseudo labels, multi-action frames, and action segments. We show that the models pretrained with the proposed self-supervised detection task outperform prior work on multiple challenging activity detection benchmarks, including Charades and MultiTHUMOS. Our extensive ablations further provide insights on when and how to use the proposed models for activity detection. Code and models will be released online.

Anomaly detection in computer vision is the task of identifying images which deviate from a set of normal images. A common approach is to train deep convolutional autoencoders to inpaint covered parts of an image and compare the output with the original image. By training on anomaly-free samples only, the model is assumed to not being able to reconstruct anomalous regions properly. For anomaly detection by inpainting we suggest it to be beneficial to incorporate information from potentially distant regions. In particular we pose anomaly detection as a patch-inpainting problem and propose to solve it with a purely self-attention based approach discarding convolutions. The proposed Inpainting Transformer (InTra) is trained to inpaint covered patches in a large sequence of image patches, thereby integrating information across large regions of the input image. When training from scratch, in comparison to other methods not using extra training data, InTra achieves results on par with the current state-of-the-art on the MVTec AD dataset for detection and surpassing them on segmentation.

Anomaly detection is a significant problem faced in several research areas. Detecting and correctly classifying something unseen as anomalous is a challenging problem that has been tackled in many different manners over the years. Generative Adversarial Networks (GANs) and the adversarial training process have been recently employed to face this task yielding remarkable results. In this paper we survey the principal GAN-based anomaly detection methods, highlighting their pros and cons. Our contributions are the empirical validation of the main GAN models for anomaly detection, the increase of the experimental results on different datasets and the public release of a complete Open Source toolbox for Anomaly Detection using GANs.

This paper presents a Simple and effective unsupervised adaptation method for Robust Object Detection (SimROD). To overcome the challenging issues of domain shift and pseudo-label noise, our method integrates a novel domain-centric augmentation method, a gradual self-labeling adaptation procedure, and a teacher-guided fine-tuning mechanism. Using our method, target domain samples can be leveraged to adapt object detection models without changing the model architecture or generating synthetic data. When applied to image corruptions and high-level cross-domain adaptation benchmarks, our method outperforms prior baselines on multiple domain adaptation benchmarks. SimROD achieves new state-of-the-art on standard real-to-synthetic and cross-camera setup benchmarks. On the image corruption benchmark, models adapted with our method achieved a relative robustness improvement of 15-25% AP50 on Pascal-C and 5-6% AP on COCO-C and Cityscapes-C. On the cross-domain benchmark, our method outperformed the best baseline performance by up to 8% AP50 on Comic dataset and up to 4% on Watercolor dataset.

In recent years, knowledge distillation has been proved to be an effective solution for model compression. This approach can make lightweight student models acquire the knowledge extracted from cumbersome teacher models. However, previous distillation methods of detection have weak generalization for different detection frameworks and rely heavily on ground truth (GT), ignoring the valuable relation information between instances. Thus, we propose a novel distillation method for detection tasks based on discriminative instances without considering the positive or negative distinguished by GT, which is called general instance distillation (GID). Our approach contains a general instance selection module (GISM) to make full use of feature-based, relation-based and response-based knowledge for distillation. Extensive results demonstrate that the student model achieves significant AP improvement and even outperforms the teacher in various detection frameworks. Specifically, RetinaNet with ResNet-50 achieves 39.1% in mAP with GID on COCO dataset, which surpasses the baseline 36.2% by 2.9%, and even better than the ResNet-101 based teacher model with 38.1% AP.

Generative adversarial networks (GANs) are able to model the complex highdimensional distributions of real-world data, which suggests they could be effective for anomaly detection. However, few works have explored the use of GANs for the anomaly detection task. We leverage recently developed GAN models for anomaly detection, and achieve state-of-the-art performance on image and network intrusion datasets, while being several hundred-fold faster at test time than the only published GAN-based method.

In one-class-learning tasks, only the normal case (foreground) can be modeled with data, whereas the variation of all possible anomalies is too erratic to be described by samples. Thus, due to the lack of representative data, the wide-spread discriminative approaches cannot cover such learning tasks, and rather generative models, which attempt to learn the input density of the foreground, are used. However, generative models suffer from a large input dimensionality (as in images) and are typically inefficient learners. We propose to learn the data distribution of the foreground more efficiently with a multi-hypotheses autoencoder. Moreover, the model is criticized by a discriminator, which prevents artificial data modes not supported by data, and enforces diversity across hypotheses. Our multiple-hypothesesbased anomaly detection framework allows the reliable identification of out-of-distribution samples. For anomaly detection on CIFAR-10, it yields up to 3.9% points improvement over previously reported results. On a real anomaly detection task, the approach reduces the error of the baseline models from 6.8% to 1.5%.

Average precision (AP), the area under the recall-precision (RP) curve, is the standard performance measure for object detection. Despite its wide acceptance, it has a number of shortcomings, the most important of which are (i) the inability to distinguish very different RP curves, and (ii) the lack of directly measuring bounding box localization accuracy. In this paper, we propose 'Localization Recall Precision (LRP) Error', a new metric which we specifically designed for object detection. LRP Error is composed of three components related to localization, false negative (FN) rate and false positive (FP) rate. Based on LRP, we introduce the 'Optimal LRP', the minimum achievable LRP error representing the best achievable configuration of the detector in terms of recall-precision and the tightness of the boxes. In contrast to AP, which considers precisions over the entire recall domain, Optimal LRP determines the 'best' confidence score threshold for a class, which balances the trade-off between localization and recall-precision. In our experiments, we show that, for state-of-the-art object (SOTA) detectors, Optimal LRP provides richer and more discriminative information than AP. We also demonstrate that the best confidence score thresholds vary significantly among classes and detectors. Moreover, we present LRP results of a simple online video object detector which uses a SOTA still image object detector and show that the class-specific optimized thresholds increase the accuracy against the common approach of using a general threshold for all classes. We provide the source code that can compute LRP for the PASCAL VOC and MSCOCO datasets in //github.com/cancam/LRP. Our source code can easily be adapted to other datasets as well.

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