*Article* **Online Learned Siamese Network with Auto-Encoding Constraints for Robust Multi-Object Tracking**

#### **Peixin Liu, Xiaofeng Li \*, Han Liu and Zhizhong Fu**

School of Information and Communication Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China; pxl@std.uestc.edu.cn (P.L.); hanliu@std.uestc.edu.cn (H.L.); fuzz@uestc.edu.cn (Z.F.)

**\*** Correspondence: xfli@uestc.edu.cn; Tel.: +86-028-61830690

Received: 3 May 2019; Accepted: 22 May 2019; Published: 28 May 2019

**Abstract:** Multi-object tracking aims to estimate the complete trajectories of objects in a scene. Distinguishing among objects efficiently and correctly in complex environments is a challenging problem. In this paper, a Siamese network with an auto-encoding constraint is proposed to extract discriminative features from detection responses in a tracking-by-detection framework. Different from recent deep learning methods, the simple two layers stacked auto-encoder structure enables the Siamese network to operate efficiently only with small-scale online sample data. The auto-encoding constraint reduces the possibility of overfitting during small-scale sample training. Then, the proposed Siamese network is improved to extract the previous-appearance-next vector from tracklet for better association. The new feature integrates the appearance, previous, and next stage motions of an element in a tracklet. With the new features, an online incremental learned tracking framework is established. It contains reliable tracklet generation, data association to generate complete object trajectories, and tracklet growth to deal with missing detections and to enhance the new feature for tracklet. Benefiting from discriminative features, the final trajectories of objects can be achieved by an efficient iterative greedy algorithm. Feature experiments show that the proposed Siamese network has advantages in terms of both discrimination and correctness. The system experiments show the improved tracking performance of the proposed method.

**Keywords:** multi-object tracking; Siamese network; discriminative feature; online learning
