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A Self-Supervised Gait Encoding Approach with Locality-Awareness for 3D Skeleton Based Person Re-Identification

By Haocong Rao, Siqi Wang, Xiping Hu, Mingkui Tan, Huang Da, Jun Cheng, Xinwang, Liu, and Bin Hu. In T-PAMI 2021 (TPAMI Featured Article).

To the best of our knowledge, this is the first skeleton-based person re-identification work formally published in the TPAMI journal.

Introduction

This is the official implementation of the self-supervised gait encoding approach presented by "A Self-Supervised Gait Encoding Approach with Locality-Awareness for 3D Skeleton Based Person Re-Identification". The codes are used to reproduce experimental results of the proposed Contrastive Attention-basd Gait Encodings (CAGEs) in the paper.

Abstract: Person re-identification (Re-ID) via gait features within 3D skeleton sequences is a newly-emerging topic with several advantages. Existing solutions either rely on hand-crafted descriptors or supervised gait representation learning. This paper proposes a self-supervised gait encoding approach that can leverage unlabeled skeleton data to learn gait representations for person Re-ID. Specifically, we first create self-supervision by learning to reconstruct unlabeled skeleton sequences reversely, which involves richer high-level semantics to obtain better gait representations. Other pretext tasks are also explored to further improve self-supervised learning. Second, inspired by the fact that motion's continuity endows adjacent skeletons in one skeleton sequence and temporally consecutive skeleton sequences with higher correlations (referred as locality in 3D skeleton data), we propose a locality-aware attention mechanism and a locality-aware contrastive learning scheme, which aim to preserve locality-awareness on intra-sequence level and inter-sequence level respectively during self-supervised learning. Last, with context vectors learned by our locality-aware attention mechanism and contrastive learning scheme, a novel feature named Constrastive Attention-based Gait Encodings (CAGEs) is designed to represent gait effectively. Empirical evaluations show that our approach significantly outperforms skeleton-based counterparts by 15-40% Rank-1 accuracy, and it even achieves superior performance to numerous multi-modal methods with extra RGB or depth information.

Requirements

• Python 3.5
• Tensorflow 1.10.0 (GPU)

Datasets

We provide three already pre-processed datasets (BIWI, IAS, KGBD) with various sequence lengths on <br/> https://pan.baidu.com/s/1u5PvudgABe63A43NuaDBpA       password：  ttyp <br/> All the best models reported in our paper can be acquired on <br/> https://pan.baidu.com/s/1sC0mjVTAhA5qq6I73rPA_g       password：  g3l3 <br/> Please download the pre-processed datasets Datasets/ and the model files Models/ into the current directory. <br/><br/> We also provide the pre-trained gait encoding models on <br/> https://pan.baidu.com/s/1aH0dBY5kpTaMVR9XxM89iw       password：  xkax <br/> Please download the pre-trained gait encoding models into the directory Models/. <br/>

The original datasets can be downloaded here: BIWI and IAS-Lab, KGBD, KS20.

Note: The access to the Vislab Multi-view KS20 dataset is available upon request. If you have signed the license agreement and been granted the right to use it, please contact me and I will share the pre-processed KS20 data.

Usage

To (1) train the self-supervised gait encoding model to obtain CAGEs and (2) validate the effectiveness of CAGEs for person Re-ID on a specific dataset with a recognition network, simply run the following command:

python train.py --dataset BIWI

# Default options: --attention LA --dataset BIWI --length 6 --t 0.1 --train_flag 1 --model rev_rec --gpu 0
# --attention: [LA, BA]  
# --dataset [BIWI, IAS, KGBD, KS20]  
# --length [4, 6, 8, 10] 
# --t [0.05, 0.1 (for BIWI/IAS/KS20), 0.5 (for KGBD), 0.8, 1.0] 
# --train_flag [1 (for training gait encoding models+RN), 0 (for training RN)] 
# --model [rev_rec, prediction, sorting, rev_rec_plus] Note that "rev_rec_plus" will train three types of models sequentially.
# --gpu [0, 1, ...]

Please see train.py for more details.

To print evaluation results (Re-ID Confusion Matrix / Rank-n Accuracy / Rank-1 Accuracy / nAUC) of the best model, run:

python evaluate.py --dataset BIWI --best_model rev_rec

# --dataset [BIWI, IAS, KGBD, KS20] 
# --best_model [rev_rec, rev_rec_plus] 

To evaluate the already trained model saved in Models/CAGEs_RN_models/model_name, run:

python evaluate.py --RN_dir model_name

Please see evaluate.py for more details.

Application to Model-Estimated Skeleton Data

To extend our model to a large RGB-based gait dataset (CASIA B), we exploit pose estimation methods to extract 3D skeletons from RGB videos of CASIA B as follows:

• Step 1: Download CASIA-B Dataset
• Step 2: Extract the 2D human body joints by using OpenPose
• Step 3: Estimate the 3D human body joints by using 3DHumanPose

Here we thank (rijun.liao@gmail.com) for his contribution of extracting 3D skeleton data from CASIA B.

We provide already pre-processed skeleton data of CASIA B for Cross-View Evaluation (CVE) (f=20/30/40) and Condition-based Matching Evaluation (CME) (f=50/60/70) on <br/> https://pan.baidu.com/s/1cRCMkHNnV0VXCgotDqS43w       password：  f6x0 <br/> Please download the two pre-processed datasets into the directory Datasets/. <br/> Note: CASIA/ is used for the CVE setup and CASIA_match/ is for the CME setup.

We also provide the pre-trained gait encoding models for CVE setup (f=20) and CME setup (f=50/60/70) on <br/> https://pan.baidu.com/s/1qOxGRK86HaEXxJGaEdvBuQ       password：  phyk <br/> Please download the pre-trained gait encoding models into the directory Models/. <br/>

Usage

To (1) train the self-supervised gait encoding model to obtain frame-level CAGEs (AP) and (2) validate the effectiveness of CAGEs for person Re-ID under CVE setup, simply run the following command:

python CVE-CASIA-B.py --view 0

# Default options: --attention LA --dataset CASIA_B --length 20 --view 0 --t 0.15 --train_flag 1 --gpu 0
# --attention: [LA, BA]  
# --length [20, 30, 40] 
# --view [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 
# --train_flag [1 (for training gait encoding models+RN), 0 (for training RN)] 
# --gpu [0, 1, ...]

Please see CVE-CASIA-B.py for more details. <br/>

To (1) train the self-supervised gait encoding model to obtain sequence-level CAGEs (SC) and (2) validate the effectiveness of CAGEs for person Re-ID under CME setup, simply run the following command:

python CME-CASIA-B.py --probe_type nm.nm

# Default options: --attention LA --dataset CASIA_B --length 50 --probe_type nm.nm --t 0.15 --train_flag 1 --gpu 0
# --attention: [LA, BA]  
# --length [50, 60, 70] 
# --probe_type [nm.nm, cl.cl, bg.bg, cl.nm, bg.nm] 
# --train_flag [1 (for training gait encoding models), 0 (for CME matching)] 
# --gpu [0, 1, ...]

Please see CME-CASIA-B.py for more details.

Results

Model Size & Computational Complexity

Citation

If you find this code useful for your research, please cite our paper

@article{rao2021self,
  title={A self-supervised gait encoding approach with locality-awareness for 3D skeleton based person re-identification},
  author={Rao, Haocong and Wang, Siqi and Hu, Xiping and Tan, Mingkui and Guo, Yi and Cheng, Jun and Liu, Xinwang and Hu, Bin},
  journal={IEEE Transactions on Pattern Analysis and Machine Intelligence},
  year={2021},
  publisher={IEEE}
}

@inproceedings{DBLP:conf/ijcai/RaoW0TD0020,
  author    = {Haocong Rao and
               Siqi Wang and
               Xiping Hu and
               Mingkui Tan and
               Huang Da and
               Jun Cheng and
               Bin Hu},
  title     = {Self-Supervised Gait Encoding with Locality-Aware Attention for Person
               Re-Identification},
  booktitle = {IJCAI},
  pages     = {898--905},
  publisher = {ijcai.org},
  year      = {2020}
}

More awesome skeleton-based models are collected in our Awesome-Skeleton-Based-Models.

License

Locality-Awareness-SGE is released under the MIT License.