Look Closer to Segment Better

Look Closer to Segment Better: Boundary Patch Refinement for Instance Segmentation (CVPR 2021)

PBR is a conceptually simple yet effective post-processing refinement framework to improve the boundary quality of instance segmentation. Following the idea of looking closer to segment boundaries better, BPR extracts and refines a series of small boundary patches along the predicted instance boundaries. The proposed BPR framework (as shown below) yields significant improvements over the Mask R-CNN baseline on the Cityscapes benchmark, especially on the boundary-aware metrics.


Prepare patches dataset [optional]

First, you need to generate the instance segmentation results on the Cityscapes training and validation set, as the following format:

- aachen_000000_000019_leftImg8bit_pred.txt
- aachen_000001_000019_leftImg8bit_0_person.png
- aachen_000001_000019_leftImg8bit_10_car.png
- ...

- frankfurt_000001_064130_leftImg8bit_pred.txt
- frankfurt_000001_064305_leftImg8bit_0_person.png
- frankfurt_000001_064305_leftImg8bit_10_motorcycle.png
- ...

The content of the txt file is the same as the standard format required by cityscape script, e.g.:

frankfurt_000000_000294_leftImg8bit_0_person.png 24 0.9990299940109253
frankfurt_000000_000294_leftImg8bit_1_person.png 24 0.9810258746147156

Then use the provided script to generate the training set:

sh tools/prepare_dataset.sh \
  maskrcnn_train \
  maskrcnn_val \

Note that this step can take about 2 hours. Feel free to skip it by downloading the processed training set.

Train the network

Point DATA_ROOT to the patches dataset and run the training script

DATA_ROOT=maskrcnn_r50/patches \
bash tools/dist_train.sh \
  configs/bpr/hrnet18s_128.py \


Suppose you have some instance segmentation results of Cityscapes dataset, as the following format:

- frankfurt_000001_064130_leftImg8bit_pred.txt
- frankfurt_000001_064305_leftImg8bit_0_person.png
- frankfurt_000001_064305_leftImg8bit_10_motorcycle.png
- ...

We provide a script (tools/inference.sh) to perform refinement operation, usage:

IMG_DIR=data/cityscapes/leftImg8bit/val \
GT_JSON=data/cityscapes/annotations/instancesonly_filtered_gtFine_val.json \
GPUS=4 \
sh tools/inference.sh configs/bpr/hrnet48_256.py ckpts/hrnet48_256.pth maskrcnn_val maskrcnn_val_refined

The refinement results will be saved in maskrcnn_val_refined/refined.

For COCO model, use tools/inference_coco.sh instead.


Backbone Dataset Config Checkpoint
HRNet-18s Cityscapes hrnet18s_128.py Tsinghua Cloud
HRNet-48 Cityscapes hrnet48_256.py Tsinghua Cloud
HRNet-18s COCO hrnet18s_128.py Tsinghua Cloud


This project is based on mmsegmentation code base.


If you find this project useful in your research, please consider citing:

  title={Look Closer to Segment Better: Boundary Patch Refinement for Instance Segmentation},
  author={Chufeng Tang and Hang Chen and Xiao Li and Jianmin Li and Zhaoxiang Zhang and Xiaolin Hu},
  journal={arXiv preprint arXiv:2104.05239},