Abstract The rapid expansion of online education has heightened concerns about cyberbullying in virtual classrooms. This paper presents a comprehensive approach for detecting cyberbullying by analyzing students' engagement and emotional responses in online classrooms. Due to the influence of camera resolution and surrounding light in online classrooms, students' facial expressions are often blurry, and the changes in facial features may not be significant. Moreover, most current recognition algorithms utilize larger models, which may not be suitable for real-time detection in online environments. To address these challenges, this study introduces a student facial expression recognition (SFER) method based on an enhanced YOLOv5 (you only look once version 5) model, termed SFER-YOLOv5. Firstly, the improved Soft-NMS is employed to replace the original non-maximum suppression (NMS), effectively enhancing training efficiency. Then, the coordinate attention (CA) module is incorporated into the backbone network to improve detection accuracy, particularly in classroom settings with multiple students or when students are at a considerable distance from the camera. Next, the efficient intersection over union (EIoU) loss function is utilized. EIoU calculates width and height losses separately based on complete IoU (CIoU), replacing the aspect ratio. Finally, Focal Loss is introduced to address sample imbalance issues. The comparative results show that SFER-YOLOv5 achieves an mAP@0.5 of 78.4% on the FER-2013 dataset, 98.1% on the CK+ dataset, and 88.9% on our self-constructed dataset (SFEC). These results underscore the effectiveness of SFER-YOLOv5 in enhancing the accuracy of student facial expression recognition. The proposed method detects reduced engagement, offering a preventive strategy for mitigating cyberbullying in virtual learning environments.
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