OpenCV full name: Open Source Computer Vision Library, is an open source cross-platform computer vision library, OpenCV is mainly written in C++ language, but also provides Python and other languages, the following describes how to install OpenCV and OpenCV on the Raspberry Pi Python call library.

Update system and install dependencies:

Update Raspberry Pi:

sudo apt-get update
sudo apt-get upgrade

Installation dependencies

Install basic dependencies such as compilation:

sudo apt-get install build-essential cmake pkg-config

Install image-related libraries:

sudo apt-get install libjpeg-dev libtiff5-dev libjasper-dev libpng12-dev

Install the basic IO library:

sudo apt-get install libavcodec-dev libavformat-dev libswscale-dev libv4l-dev
sudo apt-get install libxvidcore-dev libx264-dev

Install highgui-related dependent libraries:

sudo apt-get install libgtk2.0-dev

Install opencv advanced dependency library, operation matrix, etc.:

sudo apt-get install libatlas-base-dev gfortran

Configure python virtual environment

Download OpenCV 3.1.0 and OpenCV_contrib library

cd ~ 
wget -O opencv.zip https://github.com/Itseez/opencv/archive/3.1.0.zip 
unzip opencv.zip 
wget -O opencv_contrib.zip https://github.com/Itseez/opencv_contrib/archive/3.1.0.zip 
unzip opencv_contrib.zip

Compile and install:

Compile opencv:

Enter the opencv directory:

cd opencv-3.1.0/ 
mkdir build 
cd build

Configuration cmake:

cmake -D CMAKE_BUILD_TYPE = RELEASE \ 
-D CMAKE_INSTALL_PREFIX = /usr/local \ 
-D INSTALL_PYTHON_EXAMPLES = ON \ 
-D OPENCV_EXTRA_MODULES_PATH = ~/opencv_contrib-3.1.0/modules \ 
-D BUILD.EXAMPLES = ON

Compile:

make -j4

The 4 here is for the quad-core on the Raspberry Pi, that is, it uses all the computing resources of the Raspberry Pi to compile.
If the compilation fails, you can execute the following command to retry the compilation:

make 
clean make

Note that the above command is executed only when the compilation fails.
It takes about 1 hour to compile, wait patiently, you can open the terminal to play with other things when compiling.

installation:

sudo make install

Add the dynamic link library generated by OpenCV to the Raspberry Pi directory:

sudo ldconfig

Now that it OpenCV 3.0 has been successfully installed on your machine, the next step is to cv2.so link to our virtual environment:

cd /home/pi/codes/env/cv/lib/python2.7/site-packages 
ln -s /usr/local/lib/python2.7/site-packages/cv2.so cv2.so

Note that the path of the above virtual environment needs to be modified to your own. Next, you can verify whether opencv is installed successfully, and execute it in the terminal:

python -c "import cv2;print(cv2.__version__)"

If the output is similar to the following figure, the installation is successful.