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Adrian Rosebrock has a good walkthrough on how to Install OpenCV 3.0 and Python 2.7+ on OSX.  However if you want to use Python 3, the OpenCV Python bindings don’t get installed correctly, if at all.

What I did to resolve:

1. Follow Adrian’s walkthrough from Steps 1-6, but be sure to use “python3” and “pip3” instead of just “python“:

  • Install Xcode
  • Install python3 via Homebrew (“brew install python3“, “brew linkapps python3“)
  • Also install virtualenv and virtualenvwrapper as directed (“pip3 install virtualenv virtualenvwrapper”), including modifying and resourcing .bash_profile
  • mkvirtualenv a new enviroment
  • Make sure numpy is installed (“pip3 install numpy”)
  • Install the other dependencies in Step 6: cmake, jpeg, libpng, etc.

2. In Adrian’s Step 6, get OpenCV and opencv_contrib from GitHub.  For both use the latest release if you’d like (currently 3.1.0).  So do “git checkout 3.1.0” for both OpenCV and the opencv_contrib.  You must use the same version for both.

3. For the cmake part, use the snippet below (copy & paste to get the full text).   Currently Python 3.5.1 is the latest from Homebrew but if you have a newer/different version, please adjust accordingly.  Also be sure to change the last line (OPENCV_EXTRA_MODULES_PATH variable) to the modules directory where you’ve checked out opencv_contrib from GitHub:

cmake -D CMAKE_BUILD_TYPE=RELEASE \
 -D PYTHON3_EXECUTABLE=$(which python3) \
 -D PYTHON3_INCLUDE_DIR=$(python3 -c "from distutils.sysconfig import get_python_inc; print(get_python_inc())") \
 -D PYTHON3_LIBRARY=/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/libpython3.5.dylib \
 -D PYTHON3_LIBRARIES=/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/bin \
 -D PYTHON3_INCLUDE_DIR=/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/Headers \
 -D PYTHON3_PACKAGES_PATH=$(python3 -c "from distutils.sysconfig import get_python_lib; print(get_python_lib())") \
 -D INSTALL_C_EXAMPLES=OFF -D INSTALL_PYTHON_EXAMPLES=ON \
 -D BUILD_EXAMPLES=ON \
 -D OPENCV_EXTRA_MODULES_PATH=~/opencv_contrib/modules ..

4. The cmake command above should run without errors. Check to output to see that python3 is included in the OpenCV modules to be built:

OpenCV modules:
     To be built:           core flann imgproc ml photo reg 
surface_matching video dnn fuzzy imgcodecs shape videoio highgui 
objdetect plot superres ts xobjdetect xphoto bgsegm bioinspired 
dpm face features2d line_descriptor saliency text calib3d ccalib 
datasets rgbd stereo structured_light tracking videostab 
xfeatures2d ximgproc aruco optflow stitching python2 python3

5.  If python3 is not included in the “to be built” modules then something is wrong.  Check the cmake variables again to make sure they are correct for your environment.

6. Assuming the python3 module is correctly listed, then you can now build OpenCV and install it: “make -j 4” followed by “sudo make install“.   On a quad-core I7 Mac you can use “make -j 8” to speed the compile up a bit.

7. Finish up with the rest of Adrian’s guide (Steps 9 and 10) to check that OpenCV has been properly installed and configured.

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