Multiple-Level Distillation for Video Fine-grained Accident Detection

Accident detection in surveillance or dashcam videos is a common task in the field of traffic accident analysis by using videos. However, as accidents occur sparsely and randomly in the real world, the data records are more scarce than the training data for standard detection tasks such as object detection or instance detection. Moreover, the limited and diverse accident data makes it more difficult to model the accident pattern for fine-grained accident detection tasks analyzing the accident in detail. Extra prior information should be introduced in the tasks such as the common vision feature which could offer relatively effective information for many vision tasks. The big model could generate the common vision feature by training on abundant data and consuming a lot of computing time and resources. Even though the accident video data is special, the big model could also extract common vision features. Thus, in this paper, we propose to apply knowledge distillation to fine-grained accident detection which analyzes the spatial temporal existence and severity for solving the issues of complex computing (distillation to the small model) and keeping good performance under limited accident data. Knowledge distillation could offer extra general vision feature information from the pre-trained big model. Common knowledge distillation guides the student network to learn the same representations from the teacher network by logit mimicking or feature imitation. However, single-level distillation could only focus on one aspect of mimicking classification logit or deep features. Multiple tasks with different focuses are required for fine-grained accident detection, such as multiple accident classification, temporal-spatial accident region detection, and accident severity estimation. Thus in this paper, multiple-level distillation is proposed for the different modules to generate the unified video feature concerning all the tasks in fine-grained accident detection analysis. The various experimental results on a fine-grained accident detection dataset which provides more detailed annotations of accidents demonstrate that our method could effectively model the video feature for multiple tasks.