Multiplicative angular margin loss for text-based person search

Text-based person search aims at retrieving the most relevant pedestrian images from database in response to a query in form of natural language description. Existing algorithms mainly focus on embedding textual and visual features into a common semantic space so that the similarity score of features from different modalities can be computed directly. Softmax loss is widely adopted to classify textual and visual features into a correct category in the joint embedding space. However, softmax loss can only help classify features but not increase the intra-class compactness and inter-class discrepancy. To this end, we propose multiplicative angular margin (MAM) loss to learn angularly discriminative features for each identity. The multiplicative angular margin loss penalizes the angle between feature vector and its corresponding classifier vector to learn more discriminative feature. Moreover, to focus more on informative image-text pair, we propose pairwise similarity weighting (PSW) loss to assign higher weight to informative pairs. Extensive experimental evaluations have been conducted on the CUHK-PEDES dataset over our proposed losses. The results show the superiority of our proposed method. Code is available at https://github.com/pengzhanguestc/MAM_loss.