Non-overlapping Camera Views Research Articles

A Versatile Framework for Multi-Scene Person Re-Identification.

Person Re-identification (ReID) has been extensively developed for a decade in order to learn the association of images of the same person across non-overlapping camera views. To overcome significant variations between images across camera views, mountains of variants of ReID models were developed for solving a number of challenges, such as resolution change, clothing change, occlusion, modality change, and so on. Despite the impressive performance of many ReID variants, these variants typically function distinctly and cannot be applied to other challenges. To our best knowledge, there is no versatile ReID model that can handle various ReID challenges at the same time. This work contributes to the first attempt at learning a versatile ReID model to solve such a problem. Our main idea is to form a two-stage prompt-based twin modeling framework called VersReID. Our VersReID firstly leverages the scene label to train a ReID Bank that contains abundant knowledge for handling various scenes, where several groups of scene-specific prompts are used to encode different scene-specific knowledge. In the second stage, we distill a V-Branch model with versatile prompts from the ReID Bank for adaptively solving the ReID of different scenes, eliminating the demand for scene labels during the inference stage. To facilitate training VersReID, we further introduce the multi-scene properties into self-supervised learning of ReID via a multi-scene prioris data augmentation (MPDA) strategy. Through extensive experiments, we demonstrate the success of learning an effective and versatile ReID model for handling ReID tasks under multi-scene conditions without manual assignment of scene labels in the inference stage, including general, low-resolution, clothing change, occlusion, and cross-modality scenes. Codes and models will be made publicly available.

CMOT: A cross-modality transformer for RGB-D fusion in person re-identification with online learning capabilities

Person re-identification (reID) is a crucial aspect of intelligent surveillance systems, enabling the recognition of individuals across non-overlapping camera views. As compared to the RGB modality, RGB-D based reID has the potential to achieve robust and high performance by leveraging rich complementary features of both modalities, making it applicable in various occluded scenarios. However, current multimodal reID approaches often rely on late fusion or feature-level fusion techniques to combine multiple modalities, which limits their ability to proficiently exploit complementary visual and depth-related semantic information and capture complex interactions between unimodal features. To address these limitations, this paper introduces a cross-modality online transformer (CMOT) for RGB-D based person reID with online learning capabilities, which effectively utilizes both RGB and depth modalities for the extraction of spatio-temporal features and fuses across modalities. Our CMOT is composed of three main components: (1) a hypothesis generation module based on a person detector and tracker, (2) dual-stream feature extractors via convolutional neural networks (CNNs), (3) and a fusion transformer based on a self-attention-driven self-attentive modality refinement module (SAMR) and a cross-attention-driven cross-attentive modality interaction module (CAMI) to refine and fuse RGB-D complementary features extracted from the dual-stream, RGB and depth stream, CNNs. Additionally, we introduce a bottleneck enhancement feed-forward block to enhance the model’s representation capability within SAMR and CAMI, significantly reducing parameters and computations compared to the traditional feed-forward network. Moreover, we design the triplet loss function with distance measuring ability for incorporating online learning and finally CMOT works as a few-shot network for reID. Experimental results on three RGB-D person re-identification datasets, namely BIWI RGBD-ID, RobotPKU RGBD-ID, and TVPR2, demonstrate the effectiveness and robustness of CMOT.

Cross-modal Person Re-identification Based on Hybrid Learning Networks

Objective: Person re-identification (cross-modal person re-identification, Re-ID) aims to retrieve query identities from a gallery of non-overlapping camera views. It has many practical applications such as missing person search, forensics, etc. Much pedestrian Re-ID research mainly focuses on single-modal retrieval tasks, where both indoor and outdoor pedestrian images are from red, green, and blue (RGB) modalities. However, the security monitoring system will automatically switch from the visible state to the infrared state in dark situations. In order to meet the needs of practical applications, research on cross-modal pedestrian Re-ID based on IR-RGB has attracted more and more attention. The features of different modality images essentially lack modality sharing information. Methods: Most of the existing methods use the network to extract shared features to deal with differences, but they ignore the unique feature information that is beneficial to recognition in these two modality images. In this paper, a hybrid learning network is proposed to solve the problem of learning the unique and common features of the two modalities by mixing the single-modal branch and the cross-modal branch to learn from each other. At the same time, the graph convolution attention mechanism and granular feature learning are used to process the features extracted by the cross-modal branch and the single-modal branch, so as to enrich the information input by different branch classifiers, thereby improving the discriminability of features. Results: And achieved 59.68% Rank-1 accuracy and 58.28% mean average precision average mean precision on the cross-modal data set SYSU-MM01. Conclusion: The experimental results also show that this is the effectiveness of the method.

Multi-Level Progressive Learning for Unsupervised Vehicle Re-Identification

Vehicle re-identification (ReID) technology has played a more and more important role in Intelligent Transport System (ITS), which aims at searching the same query vehicle identity from a large amount of gallery datasets under different non-overlapping camera views. Current related researches mainly focus on discriminative feature mining of vehicle images and train the model in a fully supervised manner which highly relies on the manual annotations of training data. However, it is labor-consuming and impractical to generate the annotation for each sample image in real-word applications especially for those large-scale transport systems with tons of surveillance data. To this point, we propose in this paper a multi-level progressive learning (MLPL) method for unsupervised vehicle ReID, which gives a good performance by only utilizing the unlabeled target domain images. We firstly introduce a multi-branch architecture to explore the vehicle representations in different level, which consists of one branch for global feature and two branches for local feature learning. A density-based clustering method is employed to generate pseudo labels. Combining with the unique model, we propose a novel re-clustering method to better mine the labels with high reliability. Then a dynamic progressive contrast learning (DPCL) strategy is carefully designed to train the network based on these clustered labels. DPCL could dynamically adjust the training process to maximally strengthen the multi-level feature learning. Moreover, we further propose a self-adaptive loss balance method to automatically compute the weights of different losses during each training iteration. Comprehensive experiments are conducted on several mainstream evaluation datasets, including VeRi776, VehicleID and CityFlowV2-ReID. Compared to other existed unsupervised methods, our approach achieves the new state-of-the-art performance.

Gait-Assisted Video Person Retrieval

Video person retrieval aims at matching video clips of the same person across non-overlapping camera views, where video sequences contain more comprehensive information, e.g., temporal cues. How to extract useful temporal cues is the key to the success of a video person retrieval system. Gait, as a unique biometric modality indicating the way people walk, contains informative temporal information. To date, it is not clear how to fully utilize gait to boost the performance of video person retrieval. In this paper, to validate whether gait could help retrieve person in videos, we build a two-stream architecture, named appearance-gait network (AGNet), to jointly learn the appearance features and gait features from RGB video clips and silhouette video clips. We further explore how to fully utilize gait features to enhance the video feature representation. Specifically, we propose an appearance-gait attention module (AGA) to fuse a discriminative feature representation for the person retrieval task. Furthermore, to eliminate the requirement of silhouette video clips during inference, we propose a simple yet effective appearance-gait distillation module (AGD) which transfers the gait knowledge to appearance stream. As such, we are able to perform the enhanced video person retrieval without silhouette video clips, which makes the inference more flexible and practical. To the best of our knowledge, our work is the first to successfully introduce such appearance-gait knowledge distillation design for video person retrieval. We verify the effectiveness of the proposed methods on two large-scale challenging benchmarks of MARS and DukeMTMC-VideoReID. Extensive experiments demonstrate superior or comparable performance compared to the state-of-the-art methods while being much simpler. Source code is publicly available at <uri xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">https://github.com/yangyangkiki/Gait-Assisted-Video-Reid</uri> .

Mini-transformer with pooling for unsupervised domain adaptation person reidentification

Person reidentification (Re-ID) aims to match specific pedestrians across nonoverlapping camera views. Due to the dramatic disparities between different datasets, transferring a Re-ID model trained on the source domain to the target domain is challenging. Some outstanding unsupervised domain adaptation (UDA) Re-ID methods use clustering to generate pseudolabels, optimizing the model on the target domain, but the pseudolabels are inevitably noisy. To address the above issues, we propose a framework named mini-transformer with pooling (MTP) to facilitate the generation of superior quality pseudolabels by improving the model’s feature representation capability. First, we introduce an effective mini-transformer (MT) that can be placed directly behind the CNNs as a feature extractor to capture long-range dependency. Then, we design two delicate pooling methods named global hybrid pooling (GHP) and global subvalue pooling (GSVP) to suit mini-transformer’s tremendous capability without increasing computational complexity. Specifically, GHP can keep more global information and GSVP can keep more discriminative information. Finally, experiments on four mainstream UDA Re-ID tasks demonstrate that MTP achieves competitive mAP and rank-1 accuracy to the current state-of-the-art methods, suggesting that our technique is simple but effective. In addition to UDA Re-ID, our MTP can be extended to other supervised retrieval tasks.

Learning global and local features using graph neural networks for person re-identification

Person re-identification (re-id) is the task of recognizing an individual across non-overlapping camera views. Some approaches only rely on extracting global appearance features from images and fail to consider people’s local body information (head, foot, body shape), which can be used as complementary. Other techniques combine local and global features but rely on external information such as pedestrian attributes or human pose to locate and align the local regions. This strategy increases the learning difficulty and is not efficient or robust to real-world scenarios. In this paper, we propose an end-to-end deep learning framework to overcome these limitations. Our method combines the global and local feature representations of a pedestrian and captures the body structural information by modeling the spatial relation of patches using graph neural networks. We also represent the relationships between probe–gallery pairs using a graph neural network and propose incorporating a scoring function to mine a correspondence for local regions. Experimental results on several datasets validate the effectiveness of the proposed method.

Vehicle and Person Re-Identification With Support Neighbor Loss.

One of the key tasks for an intelligent visual surveillance system is to automatically re-identify objects of interest, e.g., persons or vehicles, from nonoverlapping camera views. This demand incurs the vast investigation of person re-identification (re-ID) and vehicle re-ID techniques, especially those deep learning-based ones. While most recent algorithms focus on designing new convolutional neural networks, less attention is paid to the loss functions, which are of vital roles as well. Triplet loss and softmax loss are the two losses that are extensively used, both of which, however, have limitations. Triplet loss optimizes the model to produce features with which samples from the same class have higher similarity than those from different classes. The problem of triplet loss is that the number of triplets to be constructed grows cubically with training samples, which causes scalability issue, unstable performance, and slow convergence. Softmax loss has favorable scalable property and is widely used for large-scale classification problems. However, since Softmax loss only aims to separate well training classes, its performance for re-ID tasks is not desirable because the model is tested to measure the similarity of samples from unseen classes. We propose the support neighbor (SN) loss, which avoids the limitations of the abovementioned two losses. Unlike triplet loss that is calculated based on triplets, SN loss is derived from K -nearest neighbors (SNs) of anchor samples. The SNs of an anchor are unique, containing more valuable contextual information and neighborhood structure of the anchor, and thus contribute to more stable performance and reliable embedding from image space to feature space. Based on the SNs, a softmax-like separation term and a squeeze term are proposed, which encourage interclass separation and intraclass compactness, respectively. Experiments show that SN loss surpasses triplet and softmax losses with the same backbone network and reaches the state-of-the-art performance for both person and vehicle re-ID using a ResNet50 backbone when combined with training tricks.

Dual-Stream Guided-Learning via a Priori Optimization for Person Re-identification

The task of person re-identification (re-ID) is to find the same pedestrian across non-overlapping camera views. Generally, the performance of person re-ID can be affected by background clutter. However, existing segmentation algorithms cannot obtain perfect foreground masks to cover the background information clearly. In addition, if the background is completely removed, some discriminative ID-related cues (i.e., backpack or companion) may be lost. In this article, we design a dual-stream network consisting of a Provider Stream (P-Stream) and a Receiver Stream (R-Stream). The R-Stream performs an a priori optimization operation on foreground information. The P-Stream acts as a pusher to guide the R-Stream to concentrate on foreground information and some useful ID-related cues in the background. The proposed dual-stream network can make full use of the a priori optimization and guided-learning strategy to learn encouraging foreground information and some useful ID-related information in the background. Our method achieves Rank-1 accuracy of 95.4% on Market-1501, 89.0% on DukeMTMC-reID, 78.9% on CUHK03 (labeled), and 75.4% on CUHK03 (detected), outperforming state-of-the-art methods.

Deep progressive attention for person re-identification

Person re-identification (Re-ID) aims to retrieve specific individuals across non-overlapping camera views. In recent years, attention-based models contribute to many computer vision tasks due to their great ability for learning discriminative features. We propose the deep progressive attention (DPA) in a more natural manner for person Re-ID. Similar to human visual attention mechanism, the proposed DPA progressively selects the most discriminative parts of a specific individual and formulates feature representation for comparison purpose. Concretely, on the one hand, the proposed DPA uses a long-term reward to optimize the discriminative feature selection. On the other hand, a deep convolutional architecture is integrated into a recurrent model for feature representation learning. Extensive experiments on three person Re-ID benchmarks Market-1501, DukeMTMC-reID, and CUHK03-NP demonstrate the proposed DPA is on par with the state-of-the-art. Moreover, the experiments on partial person Re-ID datasets indicate the proposed DPA is competitive with the specially designed partial person Re-ID methods.

Deep Graph Metric Learning for Weakly Supervised Person Re-Identification.

In conventional person re-identification (re-id), the images used for model training in the training probe set and training gallery set are all assumed to be instance-level samples that are manually labeled from raw surveillance video (likely with the assistance of detection) in a frame-by-frame manner. This labeling across multiple non-overlapping camera views from raw video surveillance is expensive and time consuming. To overcome these issues, we consider a weakly supervised person re-id modeling that aims to find the raw video clips where a given target person appears. In our weakly supervised setting, during training, given a sample of a person captured in one camera view, our weakly supervised approach aims to train a re-id model without further instance-level labeling for this person in another camera view. The weak setting refers to matching a target person with an untrimmed gallery video where we only know that the identity appears in the video without the requirement of annotating the identity in any frame of the video during the training procedure. The weakly supervised person re-id is challenging since it not only suffers from the difficulties occurring in conventional person re-id (e.g., visual ambiguity and appearance variations caused by occlusions, pose variations, background clutter, etc.), but more importantly, is also challenged by weakly supervised information because the instance-level labels and the ground-truth locations for person instances (i.e., the ground-truth bounding boxes of person instances) are absent. To solve the weakly supervised person re-id problem, we develop deep graph metric learning (DGML). On the one hand, DGML measures the consistency between intra-video spatial graphs of consecutive frames, where the spatial graph captures neighborhood relationship about the detected person instances in each frame. On the other hand, DGML distinguishes the inter-video spatial graphs captured from different camera views at different sites simultaneously. To further explicitly embed weak supervision into the DGML and solve the weakly supervised person re-id problem, we introduce weakly supervised regularization (WSR), which utilizes multiple weak video-level labels to learn discriminative features by means of a weak identity loss and a cross-video alignment loss. We conduct extensive experiments to demonstrate the feasibility of the weakly supervised person re-id approach and its special cases (e.g., its bag-to-bag extension) and show that the proposed DGML is effective.

PMT-Net: Progressive Multi-Task Network for one-shot Person Re-Identification

Most existing person Re-Identification (Re-ID) algorithms require abundant labeled data from paired non-overlapping camera views in the fully supervised scenario. However, the fully supervised Re-ID suffers from the limited availability of labeled training samples due to the sharply increased cost of manual efforts. To tackle this problem, a novel Progressive Multi-Task Network (PMT-Net) for person Re-ID is proposed. PMT-Net initializes a model using only one labeled sample for each identity, and it iteratively optimizes the model by sampling the most reliable pseudo labels dynamically from unlabeled samples. Firstly, pedestrian attributes recognition is incorporated as an auxiliary task to learn discriminative features. Then, based on the discriminative features, the identity label for unlabeled samples is estimated by the distance between the labeled samples and unlabeled samples in feature space. In addition, to enhance the accuracy of label estimation for the unlabeled samples, a semi-supervised clustering method, named Distance Ranked Weight Clustering (DRW-Clustering) is designed. The clustering method weights partial unlabeled samples by the indexed ordinal of distance sorting, so that it can find the real cluster center quickly and effectively. Extensive comparative evaluation experiments are conducted on Market1501 and DukeMTMC-reID datasets, and the experimental results indicate that the proposed method achieves performance competitive or better than that of the state-of-the-art for one-shot person Re-ID.

Person Reidentification via Unsupervised Cross-View Metric Learning.

Person reidentification (Re-ID) aims to match observations of individuals across multiple nonoverlapping camera views. Recently, metric learning-based methods have played important roles in addressing this task. However, metrics are mostly learned in supervised manners, of which the performance relies heavily on the quantity and quality of manual annotations. Meanwhile, metric learning-based algorithms generally project person features into a common subspace, in which the extracted features are shared by all views. However, it may result in information loss since these algorithms neglect the view-specific features. Besides, they assume person samples of different views are taken from the same distribution. Conversely, these samples are more likely to obey different distributions due to view condition changes. To this end, this paper proposes an unsupervised cross-view metric learning method based on the properties of data distributions. Specifically, person samples in each view are taken from a mixture of two distributions: one models common prosperities among camera views and the other focuses on view-specific properties. Based on this, we introduce a shared mapping to explore the shared features. Meanwhile, we construct view-specific mappings to extract and project view-related features into a common subspace. As a result, samples in the transformed subspace follow the same distribution and are equipped with comprehensive representations. In this paper, these mappings are learned in an unsupervised manner by clustering samples in the projected space. Experimental results on five cross-view datasets validate the effectiveness of the proposed method.

Person Re-Identification Based on Graph Relation Learning

Person re-identification (Re-ID) aims to find the person across non-overlapping camera views in public places. Existing methods are getting better and better at learning finer pedestrian details, but at the same time they all ignore the relations between these details, which makes some details that are critical to discrimination unable to play a key role in decision-making. To solve this problem, we propose a graph relation learning method for person re-identification. Firstly, we use graph structure to build the relation graph, and then use the weight operation to get the relation vertices that can receive suggestions from other details. Finally, by using the collaborative training scheme to train relation vertices and regional global average features, our model can learn the relation information. Extensive experiments show that the proposed method can effectively improve the discriminative ability of the model, enhance the role of neglected important clues in decision-making, and achieve state-of-the-arts performance on the more challenging CUHK03-NP dataset.

Real-Time Vehicle Orientation Classification and Viewpoint-Aware Vehicle Re-Identification

Vehicle re-identification (re-ID) is based on identity matching of vehicles across non-overlapping camera views. Recently, the research on vehicle re-ID attracts increased attention, mainly due to its prominent industrial applications, such as post-crime analysis, traffic flow analysis, and wide-area vehicle tracking. However, despite the increased interest, the problem remains to be challenging. One of the most significant difficulties of vehicle re-ID is the large viewpoint variations due to non-standardized camera placements. In this study, to improve re-ID robustness against viewpoint variations while preserving algorithm efficiency, we exploit the use of vehicle orientation information. First, we analyze and benchmark various deep learning architectures in terms of performance, memory use, and cost on applicability to orientation classification. Secondly, the extracted orientation information is utilized to improve the vehicle re-ID task. For this, we propose a viewpoint-aware multi-branch network that improves the vehicle re-ID performance without increasing the forward inference time. Third, we introduce a viewpoint-aware mini-batching approach which yields improved training and higher re-ID performance. The experiments show an increase of 4.0% mAP and 4.4% rank-1 score on the popular VeRi dataset with the proposed mini-batching strategy, and overall, an increase of 2.2% mAP and 3.8% rank-1 score compared to the ResNet-50 baseline.

Part-based Structured Representation Learning for Person Re-identification

Person re-identification aims to match person of interest under non-overlapping camera views. Therefore, how to generate a robust and discriminative representation is crucial for person re-identification. Mining local clues from human body parts to describe pedestrians has been extensively studied in existing methods. However, existing methods locate human body parts coarsely and do not consider the relations among different local parts. To address the above problem, we propose a Part-based Structured Representation Learning (PSRL) for better exploiting local clues to improve the person representation. There are two important modules in our architecture: Local Semantic Feature Extraction and Structured Person Representation Learning. The Local Semantic Feature Extraction module is designed to extract local features from human body semantic regions. After obtaining the local features, the Structured Person Representation Learning is proposed to fuse the local features by considering the person structure. To model the underlying person structure, a graph convolutional network is employed to capture the relations of different semantic regions. The generated structured feature encodes underlying person structure information, and local semantic feature can solve the misalignment problem caused by pose variations in feature matching. By combining them together, we can improve the descriptive ability of the generated representation. Extensive evaluations on four standard benchmarks show that our proposed method achieves competitive performance against state-of-the-art methods.

View-specific subspace learning and re-ranking for semi-supervised person re-identification

Person re-identification (re-ID) focuses on matching the same person across non-overlapping camera views. Most existing methods require tedious manual annotation and can only learn a unitary transformation for images across views, which severely lack of scalability and suffer from view-specific biases. To address these issues, we put forward a View-Specific Semi-supervised Subspace Learning (VS-SSL) approach that can learn specific projections for each view, utilizing limited labeled data to guide the training while leveraging abundant unlabeled data simultaneously. Moreover, a novel re-ranking strategy is proposed to boost the performance further, which re-estimates the similarity between probe and galleries according to the overlap ratio between their expanded neighbors and their position in each other’s ranking list. The effectiveness of the proposed framework is evaluated on several widely-used datasets (VIPeR, PRID450S, PRID2011, CUHK01 and Market-1501), yielding superior performance for both semi-supervised and supervised re-ID.

An Improved Deep Mutual-Attention Learning Model for Person Re-Identification

Person re-identification is the task of matching pedestrian images across a network of non-overlapping camera views. It poses aggregated challenges resulted from random human pose, clutter from the background, illumination variations, and other factors. There has been a vast number of studies in recent years with promising success. However, key challenges have not been adequately addressed and continue to result in sub-optimal performance. Attention-based person re-identification gains more popularity in identifying discriminatory features from person images. Its potential in terms of extracting features common to a pair of person images across the feature extraction pipeline has not been be fully exploited. In this paper, we propose a novel attention-based Siamese network driven by a mutual-attention module decomposed into spatial and channel components. The proposed mutual-attention module not only leads feature extraction to the discriminative part of individual images, but also fuses mutual features symmetrically across pairs of person images to get informative regions common to both input images. Our model simultaneously learns feature embedding for discriminative cues and the similarity measure. The proposed model is optimized with multi-task loss, namely classification and verification loss. It is further optimized by a learnable mutual-attention module to facilitate an efficient and adaptive learning. The proposed model is thoroughly evaluated on extensively used large-scale datasets, Market-1501 and Duke-MTMC-ReID. Our experimental results show competitive results with the state-of-the-art works and the effectiveness of the mutual-attention module.

Enforcing Affinity Feature Learning through Self-attention for Person Re-identification

Person re-identification is the task of recognizing an individual across heterogeneous non-overlapping camera views. It has become a crucial capability needed by many applications in public space video surveillance. However, it remains a challenging task due to the subtle inter-class similarity and large intra-class variation found in person images. Current CNN-based approaches have focused and investigated traditional identification or verification frameworks. Such approaches typically use the whole input image including the background and fail to pay attention to specific body parts, deviating the feature representation learning from informative parts. In this article, we introduce a self-attention mechanism coupled with cross-resolution to improve the feature representation learning of person re-identification task. The proposed self-attention module reinforces the most informative parts from a high-resolution image using its internal representation at the low-resolution. In particular, the model is fed with a pair of images on a different scale and consists of two branches. The upper branch processes the high-resolution image and learns high dimensional feature representation while the lower branch processes the low-resolution image and learns a filtering attention heatmap. The feature maps on the lower branch are subsequently weighted to reflect the importance of each patch of the input image using a softmax operation; whereas, on the upper branch, we apply a max pooling operation to downsample the high-resolution feature map before element-wise multiplied with the attention heatmap. Our attention module helps the network learn the most discriminative visual features of multiple regions of the image and is specifically optimized to attend and enforce feature representation at different scales. Extensive experiments on three large-scale datasets show that network architectures augmented with our self-attention module systematically improve their accuracy and outperform various state-of-the-art models by a large margin.

RGB-IR Person Re-identification by Cross-Modality Similarity Preservation

Person re-identification (Re-ID) is an important problem in video surveillance for matching pedestrian images across non-overlapping camera views. Currently, most works focus on RGB-based Re-ID. However, RGB images are not well suited to a dark environment; consequently, infrared (IR) imaging becomes necessary for indoor scenes with low lighting and 24-h outdoor scene surveillance systems. In such scenarios, matching needs to be performed between RGB images and IR images, which exhibit different visual characteristics; this cross-modality matching problem is more challenging than RGB-based Re-ID due to the lack of visible colour information in IR images. To address this challenge, we study the RGB-IR cross-modality Re-ID (RGB-IR Re-ID) problem. Rather than applying existing cross-modality matching models that operate under the assumption of identical data distributions between training and testing sets to handle the discrepancy between RGB and IR modalities for Re-ID, we cast learning shared knowledge for cross-modality matching as the problem of cross-modality similarity preservation. We exploit same-modality similarity as the constraint to guide the learning of cross-modality similarity along with the alleviation of modality-specific information, and finally propose a Focal Modality-Aware Similarity-Preserving Loss. To further assist the feature extractor in extracting shared knowledge, we design a modality-gated node as a universal representation of both modality-specific and shared structures for constructing a structure-learnable feature extractor called Modality-Gated Extractor. For validation, we construct a new multi-modality Re-ID dataset, called SYSU-MM01, to enable wider study of this problem. Extensive experiments on this SYSU-MM01 dataset show the effectiveness of our method. Download link of dataset: https://github.com/wuancong/SYSU-MM01.