Seamless Scene Segmentation

CVPR | arXiv

Seamless Scene Segmentation is a CNN-based architecture that can be trained end-to-end to predict a complete class- and instance-specific labeling for each pixel in an image. To tackle this task, also known as "Panoptic Segmentation", we take advantage of a novel segmentation head that seamlessly integrates multi-scale features generated by a Feature Pyramid Network with contextual information conveyed by a light-weight DeepLab-like module.

This repository currently contains training and evaluation code for Seamless Scene Segmentation in PyTorch, based on our re-implementation of Mask R-CNN. We will soon provide pre-trained models to reproduce the Mapillary Vistas results from our paper.

If you use Seamless Scene Segmentation in your research, please cite:

@InProceedings{Porzi_2019_CVPR,
  author = {Porzi, Lorenzo and Rota Bul\`o, Samuel and Colovic, Aleksander and Kontschieder, Peter},
  title = {Seamless Scene Segmentation},
  booktitle = {The IEEE Conference on Computer Vision and Pattern Recognition (CVPR)},
  month = {June},
  year = {2019}
}

Requirements and setup

Main system requirements:

• CUDA 10.1
• Linux with GCC 7 or 8
• PyTorch v1.1.0

IMPORTANT NOTE: These requirements are not necessarily stringent, e.g. it might be possible to compile with older versions of CUDA, or under Windows. However, we have only tested the code under the above settings and cannot provide support for other setups.

To install PyTorch, please refer to https://github.com/pytorch/pytorch#installation.

To install all other dependencies using pip:

pip install -r requirements.txt

Setup

Our code is split into two main components: a library containing implementations for the various network modules, algorithms and utilities, and a set of scripts to train / test the networks.

The library, called seamseg, can be installed with:

git clone https://github.com/mapillary/seamseg.git
cd seamseg
python setup.py install

or, in a single line:

pip install git+https://github.com/mapillary/seamseg.git

The scripts do not require installation (but they do require seamseg to be installed), and can be run from the scripts/ folder. Note: Do not run the scripts from the main folder of this repo, otherwise python might decide to load the local copy of the seamseg package instead of the one installed above, causing issues.

Using the scripts

Our code uses an intermediate data format to ease training on multiple datasets, described here. We provide pre-made scripts to convert from Cityscapes and Mapillary Vistas to our format.

When training, unless explicitly training from scratch, it's also necessary to convert the ImageNet pre-trained weights provided by PyTorch to our network format. To do this, simply run:

cd scripts/utility
python convert_pytorch_resnet.py NET_NAME OUTPUT_FILE

where NET_NAME is one of resnet18, resnet34, resnet50, resnet101 or resnet152.

Training

Training involves three main steps: Preparing the dataset, creating a configuration file and running the training script. To prepare the dataset, refer to the format description here, or use one of the scripts in scripts/data_preparation. The configuration file is a simple text file in ini format. The default value of each configuration parameter, as well as a short description of what it does, is available in seamseg/config/defaults.

To launch the training:

cd scripts
python -m torch.distributed.launch --nproc_per_node=N_GPUS train_panoptic.py --log_dir LOG_DIR CONFIG DATA_DIR 

Note that, for now, our code must be launched in "distributed" mode using PyTorch's torch.distributed.launch utility. It's also highly recommended to train on multiple GPUs (possibly 4-8) in order to obtain good results. Training logs, both in text and Tensorboard formats, will be written in LOG_DIR.

The validation metrics reported in the logs include mAP, PQ and mIOU, computed as follows:

• For mAP (both mask and bounding box), we resort to the original implementation from the COCO API. This is the reason why our dataset format also includes COCO-format annotations.
• For PQ (Panoptic Quality) and mIOU we use our own implementations. Our PQ metric has been verified to produce results that are equivalent to the official implementation, minus numerical differences.

Running inference

Given a trained network, inference can be run on any set of images using scripts/test_panoptic.py:

cd scripts
python -m torch.distributed.launch --nproc_per_node=N_GPUS test_panoptic.py --meta METADATA --log_dir LOG_DIR CONFIG MODEL INPUT_DIR OUTPUT_DIR

Images (either png or jpg) will be read from INPUT_DIR and recursively in all subfolders, and predictions will be written to OUTPUT_DIR. The script also requires to be given the metadata.bin file of the dataset the network was originally trained on. Note that the script will only read from the "meta" section, meaning that a stripped-down version of metadata.bin, i.e. without the "images" section, can also be used.

By default, the test scripts output "qualitative" results, i.e. the original images superimposed with their panoptic segmentation. This can be changed by setting the --raw flag: in this case, the script will output, for each image, the "raw" network output as a PyTorch .pth.tar file. An additional script to process these raw outputs into COCO-format panoptic predictions will be released soon.