Install opencv in raspberry-pi-4.md

Download require dependencies

export DEBIAN_FRONTEND=noninteractive
sudo apt-get -q -y update
sudo apt-get -q -y install build-essential
sudo apt-get -q -y install cmake 
sudo apt-get -q -y install pkg-config 
sudo apt-get -q -y install libpng12-0 libpng12-dev libpng++-dev libpng3 
sudo apt-get -q -y install libpnglite-dev libpngwriter0-dev libpngwriter0c2 
sudo apt-get -q -y install zlib1g-dbg zlib1g zlib1g-dev 
sudo apt-get -q -y install pngtools libtiff4-dev libtiff4 libtiffxx0c2 libtiff-tools 
sudo apt-get -q -y install libjpeg8 libjpeg8-dev libjpeg8-dbg libjpeg-progs 
sudo apt-get -q -y install ffmpeg libavcodec-dev libavcodec52 libavformat52 libavformat-dev 
sudo apt-get -q -y install libgstreamer0.10-0-dbg libgstreamer0.10-0  libgstreamer0.10-dev 
sudo apt-get -q -y install libxine1-ffmpeg  libxine-dev libxine1-bin 
sudo apt-get -q -y install libunicap2 libunicap2-dev 
sudo apt-get -q -y install libdc1394-22-dev libdc1394-22 libdc1394-utils 
sudo apt-get -q -y install swig 
sudo apt-get -q -y install libv4l-0 libv4l-dev 
sudo apt-get -q -y install python-numpy 
sudo apt-get -q -y install libpython2.6 python-dev python2.6-dev 
sudo apt-get -q -y install libpython2.7 python-dev python2.7-dev 
sudo apt-get -q -y install libgtk2.0-dev pkg-config
sudo apt-get -q -y install mplayer
cd ~

Download openvc tar file from website

https://sourceforge.net/projects/opencvlibrary/files/4.2.0/OpenCV%204.2.0.tar.gz/download

extract the folder

tar -xvjpf OpenCV 4.2.0.tar.bz2

change the name of folder

mv OpenCV 4.2.0 OpenCV

change the directory

cd ~/OpenCV/

create the folder

mkdir release

change directory to the folder

cd release

Runn the cmake command

cmake -D CMAKE_BUILD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/usr/local -D BUILD_PYTHON_SUPPORT=ON -D BUILD_EXAMPLES=ON ..

this process will take 1-2 hrs

make

sudo make install