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106
Two-stream convolutional networks for action recognition in videos
- CoRR
"... We investigate architectures of discriminatively trained deep Convolutional Net-works (ConvNets) for action recognition in video. The challenge is to capture the complementary information on appearance from still frames and motion between frames. We also aim to incorporate into the network design as ..."
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Cited by 43 (3 self)
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We investigate architectures of discriminatively trained deep Convolutional Net-works (ConvNets) for action recognition in video. The challenge is to capture the complementary information on appearance from still frames and motion between frames. We also aim to incorporate into the network design aspects of the best performing hand-crafted features. Our contribution is three-fold. First, we propose a two-stream ConvNet architec-ture which incorporates spatial and temporal networks. Second, we demonstrate that a ConvNet trained on multi-frame dense optical flow is able to achieve very good performance in spite of limited training data. Finally, we show that multi-task learning, applied to two different action classification datasets, can be used to increase the amount of training data and improve the performance on both. Our architecture is trained and evaluated on the standard video actions benchmarks of UCF-101 and HMDB-51, where it matches the state of the art. It also exceeds by a large margin previous attempts to use deep nets for video classification. 1
Action and Event Recognition with Fisher Vectors on a Compact Feature Set
, 2014
"... HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte p ..."
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Cited by 38 (7 self)
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HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et a ̀ la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Bag of Visual Words and Fusion Methods for Action Recognition: Comprehensive Study and Good Practice
, 2014
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Spatio-Temporal Object Detection Proposals
"... Abstract. Spatio-temporal detection of actions and events in video is a challeng-ing problem. Besides the difficulties related to recognition, a major challenge for detection in video is the size of the search space defined by spatio-temporal tubes formed by sequences of bounding boxes along the fra ..."
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Cited by 11 (1 self)
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Abstract. Spatio-temporal detection of actions and events in video is a challeng-ing problem. Besides the difficulties related to recognition, a major challenge for detection in video is the size of the search space defined by spatio-temporal tubes formed by sequences of bounding boxes along the frames. Recently methods that generate unsupervised detection proposals have proven to be very effective for object detection in still images. These methods open the possibility to use strong but computationally expensive features since only a relatively small number of detection hypotheses need to be assessed. In this paper we make two contribu-tions towards exploiting detection proposals for spatio-temporal detection prob-lems. First, we extend a recent 2D object proposal method, to produce spatio-temporal proposals by a randomized supervoxel merging process. We introduce spatial, temporal, and spatio-temporal pairwise supervoxel features that are used to guide the merging process. Second, we propose a new efficient supervoxel method. We experimentally evaluate our detection proposals, in combination with our new supervoxel method as well as existing ones. This evaluation shows that our supervoxels lead to more accurate proposals when compared to using existing state-of-the-art supervoxel methods. 1
Video action detection with relational dynamic-poselets
- In ECCV
, 2014
"... •Problem: We aim to not only recognize on-going action class (action recognition), but also localize its spatiotemporal extent (action detection), and even estimate the pose of the actor (pose estimation). •Key insights: ..."
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Cited by 11 (3 self)
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•Problem: We aim to not only recognize on-going action class (action recognition), but also localize its spatiotemporal extent (action detection), and even estimate the pose of the actor (pose estimation). •Key insights:
Action and Event Recognition with Fisher Vectors on a Compact Feature Set
"... Action recognition in uncontrolled video is an important and challenging computer vision problem. Recent progress in this area is due to new local features and models that capture spatio-temporal structure between local features, or human-object interactions. Instead of working towards more complex ..."
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Cited by 9 (5 self)
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Action recognition in uncontrolled video is an important and challenging computer vision problem. Recent progress in this area is due to new local features and models that capture spatio-temporal structure between local features, or human-object interactions. Instead of working towards more complex models, we focus on the low-level features and their encoding. We evaluate the use of Fisher vectors as an alternative to bag-of-word histograms to aggregate a small set of state-of-the-art low-level descriptors, in combination with linear classifiers. We present a large and varied set of evaluations, considering (i) classification of short actions in five datasets, (ii) localization of such actions in feature-length movies, and (iii) large-scale recognition of complex events. We find that for basic action recognition and localization MBH features alone are enough for stateof-the-art performance. For complex events we find that SIFT and MFCC features provide complementary cues. On all three problems we obtain state-of-the-art results, while using fewer features and less complex models. 1.
Weakly Supervised Action Labeling in Videos Under Ordering Constraints
"... Abstract. We are given a set of video clips, each one annotated with an ordered list of actions, such as “walk ” then “sit ” then “answer phone” extracted from, for example, the associated text script. We seek to temporally localize the individual actions in each clip as well as to learn a discrimin ..."
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Cited by 9 (1 self)
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Abstract. We are given a set of video clips, each one annotated with an ordered list of actions, such as “walk ” then “sit ” then “answer phone” extracted from, for example, the associated text script. We seek to temporally localize the individual actions in each clip as well as to learn a discriminative classifier for each action. We formulate the problem as a weakly supervised temporal assignment with ordering constraints. Each video clip is divided into small time intervals and each time interval of each video clip is assigned one action label, while respecting the order in which the action labels appear in the given annotations. We show that the action label assignment can be determined together with learning a classifier for each action in a discriminative manner. We evaluate the proposed model on a new and challenging dataset of 937 video clips with a total of 787720 frames containing sequences of 16 different actions from 69 Hollywood movies. 1
Action recognition with trajectory-pooled deep-convolutional descriptors
- In CVPR
, 2015
"... Visual features are of vital importance for human action understanding in videos. This paper presents a new video representation, called trajectory-pooled deep-convolutional descriptor (TDD), which shares the merits of both hand-crafted features [31] and deep-learned features [24]. Specifically, we ..."
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Cited by 8 (5 self)
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Visual features are of vital importance for human action understanding in videos. This paper presents a new video representation, called trajectory-pooled deep-convolutional descriptor (TDD), which shares the merits of both hand-crafted features [31] and deep-learned features [24]. Specifically, we utilize deep architectures to learn discrimi-native convolutional feature maps, and conduct trajectory-constrained pooling to aggregate these convolutional fea-tures into effective descriptors. To enhance the robustness of TDDs, we design two normalization methods to trans-form convolutional feature maps, namely spatiotemporal normalization and channel normalization. The advantages of our features come from (i) TDDs are automatically learned and contain high discriminative capacity compared with those hand-crafted features; (ii) TDDs take account of the intrinsic characteristics of temporal dimension and introduce the strategies of trajectory-constrained sampling and pooling for aggregating deep-learned features. We conduct experiments on two challenging datasets: HMD-B51 and UCF101. Experimental results show that TDDs outperform previous hand-crafted features [31] and deep-learned features [24]. Our method also achieves superior performance to the state of the art on these datasets 1.
Efficient Action Localization with Approximately Normalized Fisher Vectors
"... The Fisher vector (FV) representation is a high-dimensional extension of the popular bag-of-word represen-tation. Transformation of the FV by power and ℓ2 normal-izations has shown to significantly improve its performance, and led to state-of-the-art results for a range of image and video classifica ..."
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Cited by 7 (1 self)
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The Fisher vector (FV) representation is a high-dimensional extension of the popular bag-of-word represen-tation. Transformation of the FV by power and ℓ2 normal-izations has shown to significantly improve its performance, and led to state-of-the-art results for a range of image and video classification and retrieval tasks. These normaliza-tions, however, render the representation non-additive over local descriptors. Combined with its high dimensionality, this makes the FV computationally expensive for the pur-pose of localization tasks. In this paper we present approx-imations to both these normalizations, which yield signifi-cant improvements in the memory and computational costs of the FV when used for localization. Second, we show how these approximations can be used to define upper-bounds on the score function that can be efficiently evaluated, which enables the use of branch-and-bound search as an alterna-tive to exhaustive sliding window search. We present ex-perimental evaluation results on classification and tempo-ral localization of actions in videos. These show that the our approximations lead to a speedup of at least one or-der of magnitude, while maintaining state-of-the-art action recognition and localization performance. 1.
Efficient feature extraction, encoding and classification for action recognition
"... Local video features provide state-of-the-art performance for action recognition. While the accuracy of action recog-nition has been continuously improved over the recent years, the low speed of feature extraction and subsequent recognition prevents current methods from scaling up to real-size probl ..."
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Cited by 5 (0 self)
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Local video features provide state-of-the-art performance for action recognition. While the accuracy of action recog-nition has been continuously improved over the recent years, the low speed of feature extraction and subsequent recognition prevents current methods from scaling up to real-size problems. We address this issue and first develop highly efficient video features using motion information in video compression. We next explore feature encoding by Fisher vectors and demonstrate accurate action recogni-tion using fast linear classifiers. Our method improves the speed of video feature extraction, feature encoding and ac-tion classification by two orders of magnitude at the cost of minor reduction in recognition accuracy. We validate our approach and compare it to the state of the art on four re-cent action recognition datasets. 1.
