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This code is developed on Detectron2

Boundary-preserving Mask R-CNN
ECCV 2020
Tianheng Cheng, Xinggang Wang, Lichao Huang, Wenyu Liu

Video from Cam看世界 on Youtube.


Tremendous efforts have been made to improve mask localization accuracy in instance segmentation. Modern instance segmentation methods relying on fully convolutional networks perform pixel-wise classification, which ignores object boundaries and shapes, leading coarse and indistinct mask prediction results and imprecise localization. To remedy these problems, we propose a conceptually simple yet effective Boundary-preserving Mask R-CNN (BMask R-CNN) to leverage object boundary information to improve mask localization accuracy. BMask R-CNN contains a boundary-preserving mask head in which object boundary and mask are mutually learned via feature fusion blocks. As a result,the mask prediction results are better aligned with object boundaries. Without bells and whistles, BMask R-CNN outperforms Mask R-CNN by a considerable margin on the COCO dataset; in the Cityscapes dataset,there are more accurate boundary groundtruths available, so that BMaskR-CNN obtains remarkable improvements over Mask R-CNN. Besides, it is not surprising to observe that BMask R-CNN obtains more obvious improvement when the evaluation criterion requires better localization (e.g., AP75)



Method Backbone lr sched AP AP50 AP75 APs APm APl download
Mask R-CNN R50-FPN 1x 35.2 56.3 37.5 17.2 37.7 50.3 -
PointRend R50-FPN 1x 36.2 56.6 38.6 17.1 38.8 52.5 -
BMask R-CNN R50-FPN 1x 36.6 56.7 39.4 17.3 38.8 53.8 model
BMask R-CNN R101-FPN 1x 38.0 58.6 40.9 17.6 40.6 56.8 model
Cascade Mask R-CNN R50-FPN 1x 36.4 56.9 39.2 17.5 38.7 52.5 -
Cascade BMask R-CNN R50-FPN 1x 37.5 57.3 40.7 17.5 39.8 55.1 model
Cascade BMask R-CNN R101-FPN 1x 39.1 59.2 42.4 18.6 42.2 57.4 model


  • Initialized from ImagetNet pre-training.
Method Backbone lr sched AP download
PointRend R50-FPN 1x 35.9 -
BMask R-CNN R50-FPN 1x 36.2 model


Left: AP curves of Mask R-CNN and BMask R-CNN under different mask IoU thresholds on the COCO val2017 set, the improvement becomes more significant when IoU increases. Right: Visualizations of Mask R-CNN and BMask R-CNN. BMask R-CNN can output more precise boundaries and accurate masks than Mask R-CNN.


Install Detectron2 following the official instructions


specify a config file and train a model with 4 GPUs

cd projects/BMaskR-CNN
python --config-file configs/bmask_rcnn_R_50_FPN_1x.yaml --num-gpus 4


specify a config file and test with trained model

cd projects/BMaskR-CNN
python --config-file configs/bmask_rcnn_R_50_FPN_1x.yaml --num-gpus 4 --eval-only MODEL.WEIGHTS /path/to/model


  title={Boundary-preserving Mask R-CNN},
  author={Tianheng Cheng and Xinggang Wang and Lichao Huang and Wenyu Liu},