Efficient 3D dense residual network and its application in human action recognition
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摘要
针对3D-CNN能够较好地提取视频中时空特征但对计算量和内存要求很高的问题,本文设计了高效3D卷积块替换原来计算量大的3×3×3卷积层,进而提出了一种融合3D卷积块的密集残差网络(3D-EDRNs)用于人体行为识别。高效3D卷积块由获取视频空间特征的1×3×3卷积层和获取视频时间特征的3×1×1卷积层组合而成。将高效3D卷积块组合在密集残差网络的多个位置中,不但利用了残差块易于优化和密集连接网络特征复用等优点,而且能够缩短训练时间,提高网络的时空特征提取效率和性能。在经典数据集UCF101、HMDB51和动态多视角复杂3D人体行为数据库(DMV action3D)上验证了结合3D卷积块的3D-EDRNs能够显著降低模型复杂度,有效提高网络的分类性能,同时具有计算资源需求少、参数量小和训练时间短等优点。
Abstract
In view of the problem that 3D-CNN can better extract the spatio-temporal features in video, but it requires a high amount of computation and memory, this paper designs an efficient 3D convolutional block to replace the 3×3×3 convolutional layer with a high amount of computation, and then proposes a 3D-efficient dense residual networks (3D-EDRNs) integrating 3D convolutional blocks for human action recognition. The efficient 3D convolutional block is composed of 1×3×3 convolutional layers for obtaining spatial features of video and 3×1×1 convolutional layers for obtaining temporal features of video. Efficient 3D convolutional blocks are combined in multiple locations of dense residual network, which not only takes advantage of the advantages of easy optimization of residual blocks and feature reuse of dense connected network, but also can shorten the training time and improve the efficiency and performance of spatial-temporal feature extraction of the network. In the classical data set UCF101, HMDB51 and the dynamic multi-view complicated 3D database of human activity (DMV action3D), it is verified that the 3D-EDRNs combined with 3D convolutional block can significantly reduce the complexity of the model, effectively improve the classification performance of the network, and have the advantages of less computational resource demand, small number of parameters and short training time.
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Key words:
- machine vision /
- convolutional neural network /
- action recognition /
- video classification
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Overview
Overview: In view of the problem that 3D-CNN can better extract the spatio-temporal features in video, but it requires a high amount of computation and memory, this paper designs an efficient 3D convolutional block to replace the 3×3×3 convolutional layer with a high amount of computation, and then proposes a 3D-efficient dense residual networks (3D-EDRNs) integrating 3D convolutional blocks for human action recognition. The efficient 3D convolutional block is composed of 1×3×3 convolutional layers for obtaining spatial features of video and 3×1×1 convolutional layers for obtaining temporal features of video. The spatial dimension convolution results are directly used as the input of time dimension convolution, which is helpful to retain the original information with abundant spatio-temporal characteristics. According to the residual network, the information flow can be transmitted from the shallow layer to the deeper layer. The dense network can apply the extended repetition features to the entire network. 3D-EDRNs is designed as a combination of a small dense connection network and a residual structure, which is used to extract the spatial-temporal features of video. The new dense residual structure extends the original dense residual structure from 2D to 3D, and integrates E3DB, which can accelerate the network training and improve the performance of the residual network. Input of the add layer is processed through the structural design of the DRB, which are all feature graphs of inactivated functions, thus, 3D-EDRNs can effectively obtain the information flow between convolutional layers, which is helpful for the network to extract the spatial-temporal features. The concatenate layer can fully integrate the shallow and high level features obtained by the network. 3D-EDRNs extracts the variable and complex spatio-temporal features of video, and the information flow between convolutional layers can also be transmitted to each layer smoothly, thus improving the utilization rate of network parameters and avoiding the problem of parameter expansion of common neural networks. Efficient 3D convolutional blocks are combined in multiple locations of dense residual network, which not only takes advantage of easy optimization of residual blocks and feature reuse of dense connected network, but also can shorten the training time and improve the efficiency and performance of spatial-temporal feature extraction of the network. In the classical data set UCF101, HMDB51 and the dynamic multi-view complicated 3D database of human activity (DMV action3D), it is verified that the 3D-EDRNs combined with 3D convolutional block can significantly reduce the complexity of the model, effectively improve the classification performance of the network, and have the advantages of less computational resource demand, small number of parameters and short training time.
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表 1 不同C3D模型基于DMV action3D数据库的实验结果
Table 1. Experimental results of different C3D models based on DMV action3D database
Method Positive view
recognition accuracy/%Side view
recognition accuracy/%Dynamic view
recognition accuracy/%Model size/M C3D
C3D+E3DB36.29
39.4737.72
40.1338.26
41.961.5
26.9表 2 3D-EDRNs基于HMDB51数据库的实验结果
Table 2. Experimental results of 3D-EDRNs based on HMDB51 database
Method Accuracy/% Model size/M 3D-EDRNs(before joining E3DB)+linear SVM 70.35 4.25 3D-EDRNs(lower features are integrated into E3DB)+linear SVM 73.26 4.6 3D-EDRNs(lower features and dense blocks are integrated into E3DB)+linear SVM 73.86 4.01 3D-EDRNs(upper features, lower features and dense blocks are integrated into E3DB)+linear SVM 76.29 3.97 表 3 3D-EDRNs基于UCF101数据库的实验结果
Table 3. Experimental results of 3D-EDRNs based on UCF101 database
Method Accuracy/% Model size/M 3D-EDRNs(before joining E3DB)+linear SVM 88.3 3.84 3D-EDRNs(lower features are integrated into E3DB)+linear SVM 93.53 3.26 3D-EDRNs(lower features and dense blocks are integrated into E3DB)+linear SVM 94.06 2.66 3D-EDRNs (upper features, lower features and dense blocks are integrated into E3DB)+linear SVM 97.09 3.43 表 4 基于不同视频特征提取方法的实验结果(UCF101数据库)
Table 4. Experimental results based on different video feature extraction methods (UCF101 database)
Method Accuracy/% Model size/M Elapsed time/(ms/clip) C3D+linear SVM 82.3 78.4 22.8 LTC+linear SVM 84.8 16.1 13.8 P3D ResNet+linear SVM 88.6 98 14.3 3D-EDRNs+linear SVM 97.09 3.43 11 -
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