Decoupling Classifier for Boosting Few-shot Object Detection and Instance Segmentation
This work addresses classification bias in few-shot object detection (FSOD) and few-shot instance segmentation (FSIS) caused by instance-level label omission—where unlabeled instances in images are erroneously treated as negative examples. To mitigate this, we propose a lightweight dual-head decoupled classifier that splits the standard classification head into two parallel branches: a positive branch for explicitly modeling ground-truth instances, and a noise-negative branch for modeling pseudo-negative instances arising from label omissions. Our approach is the first to formally define and address instance-level label-omission bias. It introduces no additional parameters, computational overhead, or reliance on meta-learning, fine-tuning, or external data; instead, it operates seamlessly within standard two-stage detectors (e.g., Mask R-CNN) under conventional supervised training. Extensive experiments on PASCAL VOC and MS-COCO benchmarks demonstrate consistent and significant improvements over state-of-the-art methods for both FSOD and FSIS. The code is publicly available.