Oflibnumpy cover image

Oflibnumpy: a handy python optical flow library, based on NumPy arrays, that enables the manipulation and combination of flow fields while keeping track of valid areas (see “Usage”). It is mostly code written from scratch, but also contains useful wrappers for specific functions from libraries such as OpenCV’s remap, to integrate them with the custom flow field class introduced by oflibnumpy. If you use this code, please acknowledge us with the following citation:

  title={oflibnumpy & oflibpytorch: Optical Flow Handling and Manipulation in Python},
  author={Ravasio, Claudio S and Da Cruz, Lyndon and Bergeles, Christos},
  journal={Journal of Open Research Software (JORS)},
  note={In press}

Note there is an equivalent flow library called Oflibpytorch, mostly based on PyTorch tensors. Its code is available on Github, and the documentation is accessible on ReadTheDocs.


  • Provides a custom flow field Flow class for both forwards and backwards (‘source’ / ‘target’ based) flow fields

  • Provides class methods to create flow fields from lists of affine transforms, or a transformation matrix

  • Provides class methods to resize the flow field, visualise it, warp images, find necessary image padding

  • Provides a class method to process three different types of flow field combination operations

  • Keeps track of valid flow field areas through said operations

  • Provides alternative functions to avoid the explicit use of the custom flow class, with slightly limited functionality


pip install oflibnumpy


In the command line, navigate to the folder oflibnumpy/tests and run:

python -m unittest discover .

Code example:

import oflibnumpy as of
# Make a flow field and display it
shape = (300, 400)
flow = of.Flow.from_transforms([['rotation', 200, 150, -30]], shape)
Visualisation of optical flow representing a rotation
# Combine sequentially with another flow field, display the result
flow_2 = of.Flow.from_transforms([['translation', 40, 0]], shape)
result = flow.combine_with(flow_2, mode=3), show_mask_borders=True)
Visualisation of optical flow representing a rotation, translated to the right
result.show_arrows(show_mask=True, show_mask_borders=True)
Visualisation of optical flow representing a rotation, translated to the right