opencv.md

Get the prefix for the virtualenv directory and the main python installation. Note that the pyenv commands are somewhat misleading.

PREFIX_MAIN=`pyenv virtualenv-prefix`
PREFIX_VENV=`pyenv prefix`

Download opencv and opencv_contrib into a clean directory. Make a separate build directory in same directory as opencv and opencv_contrib and enter it.

mkdir build
cd build

Run cmake.

cmake -D CMAKE_BUILD_TYPE=RELEASE \
  -D CMAKE_CXX_COMPILER=g++-5 \
  -D CMAKE_C_COMPILER=gcc-5 \
  -D CMAKE_INSTALL_PREFIX="$PREFIX_VENV" \
  -D PYTHON3_EXECUTABLE="$PREFIX_VENV"/bin/python3 \
  -D PYTHON_INCLUDE_DIR="$PREFIX_MAIN"/include/python3.6m/ \
  -D PYTHON_INCLUDE_DIR2="$PREFIX_MAIN"/include/python3.6m/ \
  -D PYTHON3_PACKAGES_PATH="$PREFIX_VENV"/lib/python3.6/site-packages/ \
  -D PYTHON3_LIBRARY="$PREFIX_MAIN"/lib/libpython3.6m.so \
  -D PYTHON3_NUMPY_INCLUDE_DIRS="$PREFIX_VENV"/lib/python3.6/site-packages/numpy/core/include \
  -D BUILD_opencv_python3=ON \
  -D BUILD_opencv_legacy=OFF  \
  -D OPENCV_EXTRA_MODULES_PATH=../opencv_contrib/modules \
  ../opencv

Check the ouput and make sure python3 is properly enabled. Then build and install

make
make install

You do NOT need to run make install as root since we are installing to a virtualenv