Pytorch implementation of FlowNet 2.0: Evolution of Optical Flow Estimation with Deep Networks
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Pytorch implementation of FlowNet 2.0: Evolution of Optical Flow Estimation with Deep Networks.
FlowNet2 Caffe implementation : flownet2

Multiple GPU training is supported, and the code provides examples for training or inference on MPI-Sintel clean and final datasets. The same commands can be used for training or inference with other datasets. See below for more detail.

Inference using fp16 (half-precision) is also supported.

For more help, type

python --help

Network architectures

Below are the different flownet neural network architectures that are provided.
A batchnorm version for each network is available.

  • FlowNet2S
  • FlowNet2C
  • FlowNet2CS
  • FlowNet2CSS
  • FlowNet2SD
  • FlowNet2

Custom layers

FlowNet2 or FlowNet2C* achitectures rely on custom layers Resample2d or Correlation.
A pytorch implementation of these layers with cuda kernels are available at ./networks.
Note : Currently, half precision kernels are not available for these layers.

Data Loaders

Dataloaders for FlyingChairs, FlyingThings, ChairsSDHom and ImagesFromFolder are available in

Loss Functions

L1 and L2 losses with multi-scale support are available in


# get flownet2-pytorch source
git clone
cd flownet2-pytorch

# install custom layers

Docker image

Libraries and other dependencies for this project include: Ubuntu 16.04, Python 2.7, Pytorch 0.2, CUDNN 6.0, CUDA 8.0

A Dockerfile with the above dependencies is available

# Build and launch docker image


# Example on MPISintel Clean   
python --inference --model FlowNet2 --save_flow --inference_dataset MpiSintelClean \
--inference_dataset_root /path/to/mpi-sintel/clean/dataset \
--resume /path/to/checkpoints 

Training and validation

# Example on MPISintel Final and Clean, with L1Loss on FlowNet2 model
python --batch_size 8 --model FlowNet2 --loss=L1Loss --optimizer=Adam --optimizer_lr=1e-4 \
--training_dataset MpiSintelFinal --training_dataset_root /path/to/mpi-sintel/final/dataset  \
--validation_dataset MpiSintelClean --validation_dataset_root /path/to/mpi-sintel/clean/dataset

# Example on MPISintel Final and Clean, with MultiScale loss on FlowNet2C model 
python --batch_size 8 --model FlowNet2C --optimizer=Adam --optimizer_lr=1e-4 --loss=MultiScale --loss_norm=L1 \
--loss_numScales=5 --loss_startScale=4 --optimizer_lr=1e-4 --crop_size 384 512 \
--training_dataset FlyingChairs --training_dataset_root /path/to/flying-chairs/dataset  \
--validation_dataset MpiSintelClean --validation_dataset_root /path/to/mpi-sintel/clean/dataset

Results on MPI-Sintel

Predicted flows on MPI-Sintel


Parts of this code were derived, as noted in the code, from ClementPinard/FlowNetPytorch.