Install OpenCV 4 on Ubuntu 16.04

In this post, we will provide a bash script for installing OpenCV-4.0 (C++, Python 2.7 and Python 3.5) on Ubuntu 16.04. We will also briefly study the script to understand what’s going in it. The same script can also be used for installing OpenCV-3.4.1.

Since the script installs OpenCV in a separate directory, you can run the same script again to have both OpenCV-3.4.1 and OpenCV-4 installed on the same system.

Step 0: Select OpenCV version to install

echo "OpenCV installation by learnOpenCV.com"

echo "Select OpenCV version to install (1 or 2)"
echo "1. OpenCV 3.4.1 (default)"
echo "2. Master"

read cvVersionChoice

if [ "$cvVersionChoice" -eq 2 ]; then
        cvVersion="master"
else
	cvVersion="3.4.1"
fi

To install OpenCV-4, enter 2 and for OpenCV-3.4.1, enter 1.

We are also going to clean build directories and create installation directory.

# Clean build directories
rm -rf opencv/build
rm -rf opencv_contrib/build

# Create directory for installation
mkdir installation
mkdir installation/OpenCV-"$cvVersion"

Finally, we will be storing the current working directory in cwd variable. We are also going to refer to this directory as OpenCV_Home_Dir throughout this blog.

# Save current working directory
cwd=$(pwd)

Step 1: Update Packages

sudo apt -y update
sudo apt -y upgrade

Step 2: Install OS Libraries

sudo apt -y remove x264 libx264-dev

## Install dependencies
sudo apt -y install build-essential checkinstall cmake pkg-config yasm
sudo apt -y install git gfortran
sudo apt -y install libjpeg8-dev libjasper-dev libpng12-dev

sudo apt -y install libtiff5-dev

sudo apt -y install libtiff-dev

sudo apt -y install libavcodec-dev libavformat-dev libswscale-dev libdc1394-22-dev
sudo apt -y install libxine2-dev libv4l-dev
cd /usr/include/linux
sudo ln -s -f ../libv4l1-videodev.h videodev.h
cd $cwd

sudo apt -y install libgstreamer0.10-dev libgstreamer-plugins-base0.10-dev
sudo apt -y install libgtk2.0-dev libtbb-dev qt5-default
sudo apt -y install libatlas-base-dev
sudo apt -y install libfaac-dev libmp3lame-dev libtheora-dev
sudo apt -y install libvorbis-dev libxvidcore-dev
sudo apt -y install libopencore-amrnb-dev libopencore-amrwb-dev
sudo apt -y install libavresample-dev
sudo apt -y install x264 v4l-utils

# Optional dependencies
sudo apt -y install libprotobuf-dev protobuf-compiler
sudo apt -y install libgoogle-glog-dev libgflags-dev
sudo apt -y install libgphoto2-dev libeigen3-dev libhdf5-dev doxygen

Step 3: Install Python Libraries

sudo apt -y install python-dev python-pip python3-dev python3-pip
sudo -H pip2 install -U pip numpy
sudo -H pip3 install -U pip numpy
sudo apt -y install python3-testresources

We are also going to install virtualenv and virtualenvwrapper modules to create Python virtual environments.

# Install virtual environment
sudo -H pip2 install virtualenv virtualenvwrapper
sudo -H pip3 install virtualenv virtualenvwrapper
echo "# Virtual Environment Wrapper" >> ~/.bashrc
echo "source /usr/local/bin/virtualenvwrapper.sh" >> ~/.bashrc
cd $cwd
source /usr/local/bin/virtualenvwrapper.sh

Next, we create the Python virtual environments.

############ For Python 2 ############
# create virtual environment
mkvirtualenv OpenCV-"$cvVersion"-py2 -p python2
workon OpenCV-"$cvVersion"-py2

# now install python libraries within this virtual environment
pip install numpy scipy matplotlib scikit-image scikit-learn ipython

# quit virtual environment
deactivate
######################################

############ For Python 3 ############
# create virtual environment
mkvirtualenv OpenCV-"$cvVersion"-py3 -p python3
workon OpenCV-"$cvVersion"-py3

# now install python libraries within this virtual environment
pip install numpy scipy matplotlib scikit-image scikit-learn ipython

# quit virtual environment
deactivate
######################################

Step 4: Download opencv and opencv_contrib

git clone https://github.com/opencv/opencv.git
cd opencv
git checkout $cvVersion
cd ..

git clone https://github.com/opencv/opencv_contrib.git
cd opencv_contrib
git checkout $cvVersion
cd ..

Step 5: Compile and install OpenCV with contrib modules

First we navigate to the build directory.

cd opencv
mkdir build
cd build

Next, we start the compilation and installation process.

cmake -D CMAKE_BUILD_TYPE=RELEASE \
	        -D CMAKE_INSTALL_PREFIX=$cwd/installation/OpenCV-"$cvVersion" \
	        -D INSTALL_C_EXAMPLES=ON \
	        -D INSTALL_PYTHON_EXAMPLES=ON \
	        -D WITH_TBB=ON \
	        -D WITH_V4L=ON \
		-D WITH_QT=ON \
		-D WITH_OPENGL=ON \
		-D OPENCV_EXTRA_MODULES_PATH=../../opencv_contrib/modules \
		-D BUILD_EXAMPLES=ON ..

make -j4
make install

Finally, we create symlink in virtual environments.

# Create symlink in virtual environment
py2binPath=$(find $cwd/installation/OpenCV-$cvVersion/lib/ -type f -name "cv2.so")
py3binPath=$(find $cwd/installation/OpenCV-$cvVersion/lib/ -type f -name "cv2.cpython*.so")

# Link the binary python file
cd ~/.virtualenvs/OpenCV-$cvVersion-py2/lib/python2.7/site-packages/
ln -f -s $py2binPath cv2.so

cd ~/.virtualenvs/OpenCV-$cvVersion-py3/lib/python3.5/site-packages/
ln -f -s $py3binPath cv2.so

How to use OpenCV in C++

There are two ways to use OpenCV in C++, the preferred way is to use CMake, the other one being command line compilation using g++. We will have a look at both ways.

Using CMakeLists.txt
The basic structure of your CMakeLists.txt will stay the same. Only difference being, that you will have to set OpenCV_DIR as shown below.

SET(OpenCV_DIR <OpenCV_Home_Dir>/installation/OpenCV-3.4.1/share/OpenCV/)

For OpenCV-4, the OpenCV_DIR will be:

SET(OpenCV_DIR <OpenCV_Home_Dir>/installation/OpenCV-master/share/OpenCV/)

Make sure that you replace OpenCV_Home_Dir with correct path. For example, in my case:

SET(OpenCV_DIR /home/hp/OpenCV_installation/installation/OpenCV-3.4.1/share/OpenCV/)

Once you have made your CMakeLists.txt, follow the steps given below.

mkdir build && cd build
cmake ..
cmake --build . --config Release

This will generate your executable file in build directory.

Using g++

To compile a sample file (let’s say my_sample_file.cpp), use the following command.

g++ `pkg-config --cflags --libs <OpenCV_Home_Dir>/installation/OpenCV-3.4.1/lib/pkgconfig/opencv.pc` my_sample_file.cpp -o my_sample_file

Similarly, for OpenCV-4:

g++ `pkg-config --cflags --libs <OpenCV_Home_Dir>/installation/OpenCV-master/lib/pkgconfig/opencv.pc` my_sample_file.cpp -o my_sample_file

How to use OpenCV in Python

To use the OpenCV version installed using Python script, first we activate the correct Python Virtual Environment.

For OpenCV-3.4.1 : Python 2

workon OpenCV-3.4.1-py2

For OpenCV-3.4.1 : Python 3

workon OpenCV-3.4.1-py3

For OpenCV-4 : Python 2

workon OpenCV-master-py2

For OpenCV-4 : Python 3

workon OpenCV-master-py3

Once you have activated the virtual environment, you can enter Python shell and test OpenCV version.

ipython
import cv2
print(cv2.__version__)

Hope this script proves to be useful for you :). We will be back with installation scripts for Ubuntu 18.04 and Windows as well. Stay tuned for more interesting stuff. In case of any queries, feel free to comment below and we will get back to you as soon as possible.

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