-- original : https://arxiv.org/abs/1812.06203

Formatted Citation:

@misc{dai2018tan,
    title={TAN: Temporal Aggregation Network for Dense Multi-label Action Recognition},
    author={Xiyang Dai and Bharat Singh and Joe Yue-Hei Ng and Larry S. Davis},
    year={2018},
    eprint={1812.06203},
    archivePrefix={arXiv},
    primaryClass={cs.CV}
}

Abstract

Temporal Aggregation Network TAN decompose 3D convolutions into spatial and temporal aggregation blocks.

Reduce complexity : Only apply temporal aggregation blocks once after each spatial down-sampling layer in the network.

Dilated convolutions at different resolutions of the network helps in aggregating multi-scale spatial-temporal information.

TAN model is well suited for dense multi-label action recognition.

Difficulties:

1. In a video, multiple frames aggregated together represent a semantic label which caused more computation compared to image recognition.
2. Actions can span multiple temporal and spatial scales in videos.

Related Work

• Action recognition
  • Two-stream network comprising two parallel CNNs, one trained on RGB images and another trained on stacked optical flow fields.
  • C3D operate on a sequence of image and perform 3D convolution (\(3 \times 3 \times 3\)).
• Multi-label prediction
• Temporal action localization
  • Making dense predictions
  • Predict temporal boundaries

Model

• Proposed Temporal Aggregation Module
  • A temporal aggregation module combines multiple convolutions with different dilation factors (in the temporal domain) and stacks them across the entire network.
  • Temporal convolution is a simple 1D dilated convolution
  • Add a residual identity connection from previous layers

• Spatial information
  • The bottleneck structure from residual networks.
  • A bottleneck block: \(1\times1 \to 3\times3 \to 1 \times 1\). 3 convolution layers.
• Full Model
  • Spatial and temporal blocks stacking
  • The final architecture consists of four levels of bottleneck blocks and temporal aggregation blocks.
  • One temporal aggregation block follows after multiple bottleneck blocks
  • The weights of bottleneck blocks can be initialized using pre-trained ImageNet models.
  • Spatial resolution is reduced : 1. initial convolution and pooling layers; 2. max pooling after every level

Experiment

TAN: Temporal Aggregation Network for Dense Multi-label Action Recognition