# PyMatting: A Python Library for Alpha Matting
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We introduce the PyMatting package for Python which implements various methods to solve the alpha matting problem.
- **Website and Documentation:** [https://pymatting.github.io/](https://pymatting.github.io)
- **Benchmarks:** [https://pymatting.github.io/benchmarks.html](https://pymatting.github.io/benchmarks.html)
Given an input image and a hand-drawn trimap (top row), alpha matting estimates the alpha channel of a foreground object which can then be composed onto a different background (bottom row).
PyMatting provides:
- Alpha matting implementations for:
- Closed Form Alpha Matting [[1]](#1)
- Large Kernel Matting [[2]](#2)
- KNN Matting [[3]](#3)
- Learning Based Digital Matting [[4]](#4)
- Random Walk Matting [[5]](#5)
- Shared Sampling Matting [[6]](#6)
- Foreground estimation implementations for:
- Closed Form Foreground Estimation [[1]](#1)
- Fast Multi-Level Foreground Estimation (CPU, CUDA and OpenCL) [[7]](#7)
- Fast multithreaded KNN search
- Preconditioners to accelerate the convergence rate of conjugate gradient descent:
- The *incomplete thresholded Cholesky decomposition* (*Incomplete* is part of the name. The implementation is quite complete.)
- The V-Cycle Geometric Multigrid preconditioner
- Readable code leveraging [NumPy](https://numpy.org/), [SciPy](https://scipy.org/) and [Numba](http://numba.pydata.org/)
## Getting Started
### Requirements
Minimal requirements
* numpy>=1.16.0
* pillow>=5.2.0
* numba>=0.47.0
* scipy>=1.1.0
Additional requirements for GPU support
* cupy-cuda90>=6.5.0 or similar
* pyopencl>=2019.1.2
Requirements to run the tests
* pytest>=5.3.4
### Installation with PyPI
```bash
pip3 install pymatting
```
### Installation from Source
```bash
git clone https://github.com/pymatting/pymatting
cd pymatting
pip3 install .
```
## Example
```python
from pymatting import cutout
cutout(
# input image path
"data/lemur/lemur.png",
# input trimap path
"data/lemur/lemur_trimap.png",
# output cutout path
"lemur_cutout.png")
```
[More advanced examples](https://pymatting.github.io/examples.html)
## Trimap Construction
All implemented methods rely on trimaps which roughly classify the image into foreground, background and unknown regions.
Trimaps are expected to be `numpy.ndarrays` of type `np.float64` having the same shape as the input image with only one color-channel.
Trimap values of 0.0 denote pixels which are 100% background.
Similarly, trimap values of 1.0 denote pixels which are 100% foreground.
All other values indicate unknown pixels which will be estimated by the algorithm.
## Testing
Run the tests from the main directory:
```
python3 tests/download_images.py
pip3 install -r requirements_tests.txt
pytest
```
Currently 89% of the code is covered by tests.
## Upgrade
```bash
pip3 install --upgrade pymatting
python3 -c "import pymatting"
```
## Bug Reports, Questions and Pull-Requests
Please, see [our community guidelines](https://github.com/pymatting/pymatting/blob/master/CONTRIBUTING.md).
## Authors
- **Thomas Germer**
- **Tobias Uelwer**
- **Stefan Conrad**
- **Stefan Harmeling**
See also the list of [contributors](https://github.com/pymatting/pymatting/contributors) who participated in this project.
## Projects using PyMatting
* [Rembg](https://github.com/danielgatis/rembg) - an excellent tool for removing image backgrounds.
* [PaddleSeg](https://github.com/PaddlePaddle/PaddleSeg) - a library for a wide range of image segmentation tasks.
* [chaiNNer](https://github.com/chaiNNer-org/chaiNNer) - a node-based image processing GUI.
* [LSA-Matting](https://github.com/kfeng123/LSA-Matting) - improving deep image matting via local smoothness assumption.
## License
This project is licensed under the MIT License - see the [LICENSE.md](LICENSE.md) file for details
## Citing
If you found PyMatting to be useful for your work, please consider citing our [paper](https://doi.org/10.21105/joss.02481):
```
@article{Germer2020,
doi = {10.21105/joss.02481},
url = {https://doi.org/10.21105/joss.02481},
year = {2020},
publisher = {The Open Journal},
volume = {5},
number = {54},
pages = {2481},
author = {Thomas Germer and Tobias Uelwer and Stefan Conrad and Stefan Harmeling},
title = {PyMatting: A Python Library for Alpha Matting},
journal = {Journal of Open Source Software}
}
```
## References
[1]
Anat Levin, Dani Lischinski, and Yair Weiss. A closed-form solution to natural image matting. IEEE transactions on pattern analysis and machine intelligence, 30(2):228–242, 2007.
[2]
Kaiming He, Jian Sun, and Xiaoou Tang. Fast matting using large kernel matting laplacian matrices. In 2010 IEEE Computer Society Conference on Computer Vision and Pattern Recognition, 2165–2172. IEEE, 2010.
[3]
Qifeng Chen, Dingzeyu Li, and Chi-Keung Tang. Knn matting. IEEE transactions on pattern analysis and machine intelligence, 35(9):2175–2188, 2013.
[4]
Yuanjie Zheng and Chandra Kambhamettu. Learning based digital matting. In 2009 IEEE 12th international conference on computer vision, 889–896. IEEE, 2009.
[5]
Leo Grady, Thomas Schiwietz, Shmuel Aharon, and Rüdiger Westermann. Random walks for interactive alpha-matting. In Proceedings of VIIP, volume 2005, 423–429. 2005.
[6]
Eduardo S. L. Gastal and Manuel M. Oliveira. "Shared Sampling for Real-Time Alpha Matting". Computer Graphics Forum. Volume 29 (2010), Number 2, Proceedings of Eurographics 2010, pp. 575-584.
[7]
Germer, T., Uelwer, T., Conrad, S., & Harmeling, S. (2020). Fast Multi-Level Foreground Estimation. arXiv preprint arXiv:2006.14970.
Lemur image by Mathias Appel from https://www.flickr.com/photos/mathiasappel/25419442300/ licensed under [CC0 1.0 Universal (CC0 1.0) Public Domain License](https://creativecommons.org/publicdomain/zero/1.0/).