OpenCV-SWIG

A SWIG library for OpenCV types

This library is a collection of SWIG interface files with rules to wrap OpenCV types as Python classes. The OpenCV itself has a Python binding exposing its API, this library is not that.

This code has been tested with OpenCV versions from 2.4.11 through 3.1.0, and with Python 2.7 and 3.5.

Hello, world!

The use case of this library is when someone is writing a C++ library, which uses OpenCV types on its API, and desires to create a Python binding to that library using SWIG.

Say you have built some C++ library MyLib having a my_lib.hpp header:

#include <opencv2/core.hpp>
#include <iostream>

inline
void moveTo(cv::Point const& p)
{
    std::cout << "cv::Point moved" << std::endl;
}

inline
cv::Mat3b getImage()
{
    return cv::Mat3b(3, 5);
}

To generate a Python binding to MyLib all that is needed is a my_lib.i SWIG file as:

%module my_lib

%include <opencv.i>
%cv_instantiate_all_defaults

%{
    #include "my_lib.hpp"
%}

%include "my_lib.hpp"

Running SWIG as in:

swig -I<path to OpenCV-SWIG library> -python -c++ my_lib.i

a my_lib_wrap.cxx and my_lib.py files will be generated containing the binding source code.

In a Linux system the my_lib_wrap.cxx can be compiled to a _my_lib.so (as expected by the Python interpreter) with the command:

g++ -shared -fpic my_lib_wrap.cxx $(pkg-config --cflags python3) $(pkg-config --libs opencv) -o _my_lib.so

That will create a Python module my_lib on the current directory, and the code bellow will work just fine:

import my_lib
import numpy as np
import cv2

p0 = my_lib.Point(13, 17)
my_lib.moveTo(p0)

img = my_lib.getImage()
img = cv2.blur(np.asarray(img), (3, 3))

Installation

To install, just copy all files under the lib directory to the same directory as SWIG Python modules. Another option is move the lib directory to another path, say /home/bla/swig_libs, and call SWIG with a -I<dir> argument. Following the above example:

swig -I/home/bla/swig_libs -c++ -python my_lib.i

Testing

To build and run the tests, make a new directory inside test and change to it:

cd test
mkdir build
cd build

Inside the new created directory, to test using Python 3:

cmake ..
make
py.test ..

To test using Python 2:

cmake -DTEST_PYTHON_VERSION=2 ..
make
py.test ..

License

OpenCV-SWIG is distributed under the 3-clause BSD license.