Person re-identification in images with deep learning

Abstract : Video surveillance systems are of a great value for public safety. As one of the most import surveillance applications, person re-identification is defined as the problem of identifying people across images that have been captured by different surveillance cameras without overlapping fields of view. With the increasing need for automated video analysis, this task is increasingly receiving attention. However, this problem is challenging due to the large variations of lighting, pose, viewpoint and background. To tackle these different difficulties, in this thesis, we propose several deep learning based approaches to obtain a better person re-identification performance in different ways. In the first proposed approach, we use pedestrian attributes to enhance the person re-identification. The attributes are defined as semantic mid-level descriptions of persons, such as gender, accessories, clothing etc. They could be helpful to extract characteristics that are invariant to the pose and viewpoint variations thanks to the descriptor being on a higher semantic level. In order to make use of the attributes, we propose a CNN-based person re-identification framework composed of an identity classification branch and of an attribute recognition branch. At a later stage, these two cues are combined to perform person re-identification. Secondly, among the challenges, one of the most difficult is the variation under different viewpoint. The same person shows very different appearances from different points of view. To deal with this issue, we consider that the images under various orientations are from different domains. We propose an orientation-specific CNN. This framework performs body orientation regression in a gating branch, and in another branch learns separate orientation-specific layers as local experts. The combined orientation-specific CNN feature representations are used for the person re-identification task. Thirdly, learning a similarity metric for person images is a crucial aspect of person re-identification. As the third contribution, we propose a novel listwise loss function taking into account the order in the ranking of gallery images with respect to different probe images. Further, an evaluation gain-based weighting is introduced in the loss function to optimize directly the evaluation measures of person re-identification. At the end, in a large gallery set, many people could have similar clothing. In this case, using only the appearance of single person leads to strong ambiguities. In realistic settings, people often walk in groups rather than alone. As the last contribution, we propose to learn a deep feature representation with displacement invariance for group context and introduce a method to combine the group context and single-person appearance. For all the four contributions of this thesis, we carry out extensive experiments on popular benchmarks and datasets to demonstrate the effectiveness of the proposed systems.
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Yiqiang Chen. Person re-identification in images with deep learning. Computer Vision and Pattern Recognition [cs.CV]. Université de Lyon, 2018. English. ⟨NNT : 2018LYSEI074⟩. ⟨tel-02090746v2⟩

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