step by step to install opencv on raspberry pi !!!

install opencv raspberry pi

sudo apt-get update && sudo apt-get upgrade && sudo rpi-update
sudo nano /etc/dphys-swapfile
	CONF_SWAPSIZE=2048
sudo apt-get install build-essential cmake pkg-config
sudo apt-get install libjpeg-dev libtiff5-dev libjasper-dev libpng12-dev
sudo apt-get install libavcodec-dev libavformat-dev libswscale-dev libv4l-dev
sudo apt-get install libxvidcore-dev libx264-dev
sudo apt-get install libgtk2.0-dev libgtk-3-dev
sudo apt-get install libatlas-base-dev gfortran

wget -O opencv.zip https://github.com/opencv/opencv/archive/4.1.0.zip
wget -O opencv_contrib.zip https://github.com/opencv/opencv_contrib/archive/4.1.0.zip

unzip opencv.zip
unzip opencv_contrib.zip

sudo pip3 install numpy
cd ~/opencv-4.1.0/
mkdir build
cd build
cmake -D CMAKE_BUILD_TYPE=RELEASE \
 -D CMAKE_INSTALL_PREFIX=/usr/local \
 -D INSTALL_PYHTON_EXAMPLES=ON \
 -D OPENCV_EXTRA_MODULES_PATH=~/opencv_contrib-4.1.0/modules \
 -D BUILD_EXAMPLES=ON ..

make -j4
sudo make install && sudo ldconfig
sudo reboot