IoU-uniform R-CNN: Breaking through the limitations of RPN

Region Proposal Network (RPN) is the cornerstone of two-stage object detectors. It generates a sparse set of object proposals and alleviates the extrem foreground-background class imbalance problem during training. However, we find that the potential of the detector has not been fully exploited due to the IoU distribution imbalance and inadequate quantity of the training samples generated by RPN. With the increasing intersection over union (IoU), the exponentially smaller numbers of positive samples would lead to the distribution skewed towards lower IoUs, which hinders the optimization of detector at high IoU levels. In this paper, to break through the limitations of RPN, we propose IoU-Uniform R-CNN, a simple but effective method that directly generates training samples with uniform IoU distribution for the regression branch as well as the IoU prediction branch. Besides, we improve the performance of IoU prediction branch by eliminating the feature offsets of RoIs at inference, which helps the NMS procedure by preserving accurately localized bounding box. Extensive experiments on the PASCAL VOC and MS COCO dataset show the effectiveness of our method, as well as its compatibility and adaptivity to many object detection architectures. The code is made publicly available at https://github.com/zl1994/IoU-Uniform-R-CNN. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Region Proposal Network (RPN) is crucial in two-stage object detectors for generating object proposals and addressing foreground-background class imbalance during training. However, limitations such as IoU distribution imbalance and inadequate training samples generated by RPN have not fully exploited the detector's potential. To overcome these limitations, a simple but effective method called IoU-Uniform R-CNN is proposed to generate training samples with uniform IoU distribution, improving detection performance and compatibility with various object detection architectures.