Install OpenCV on Ubuntu

Ibmi Media
Server Management Service
49

Are you trying to install OpenCV on Ubuntu?

This guide is for you.

OpenCV (Open Source Computer Vision Library) is an open source computer vision library and has bindings for C++, Python, and Java.

OpenCV can take advantage of multi-core processing and features GPU acceleration for real-time operation.

Some of our Customers use OpenCV for a wide range of applications. Some of which are medical image analysis, surveillance video, detecting and recognizing faces, tracking moving objects, extracting 3D models, and so on.

Here at Ibmi Media, as part of our Server Management Services, we regularly help our Customers to perform Ubuntu related tasks.

In this context, we shall look into how to install OpenCV on Ubuntu 20.04.

How to install OpenCV on Ubuntu 20.04 ?

Basically, there are two different ways to install OpenCV:

i. Using Ubuntu repository.

ii. Through the source.

1. Install OpenCV from the Ubuntu Repository

OpenCV is available for installation from the default Ubuntu 20.04 repositories:

$ sudo apt update
$ sudo apt install libopencv-dev python3-opencv

Now we have all packages necessary to run OpenCV.

We verify the installation by importing the cv2 module and printing the OpenCV version:

$ python3 -c “import cv2; print(cv2.__version__)”

For example, the output will like this:

Output
4.2.0

This implies, we have the 4.2.0 OpenCV version.

2. Install OpenCV from the Source

If we build the OpenCV library from the source we can optimize it for our particular system.

In addition, we will have complete control over the build options.

Our Support Experts recommend this method of installing OpenCV.

In order to install the latest OpenCV version from the source:

i. Install the build tools and dependencies:

$ sudo apt install build-essential cmake git pkg-config libgtk-3-dev \
libavcodec-dev libavformat-dev libswscale-dev libv4l-dev \
libxvidcore-dev libx264-dev libjpeg-dev libpng-dev libtiff-dev \
gfortran openexr libatlas-base-dev python3-dev python3-numpy \
libtbb2 libtbb-dev libdc1394-22-dev libopenexr-dev \
libgstreamer-plugins-base1.0-dev libgstreamer1.0-dev

ii. Clone the OpenCV’s and OpenCV contrib repositories:

$ mkdir ~/opencv_build && cd ~/opencv_build
$ git clone https://github.com/opencv/opencv.git
$ git clone https://github.com/opencv/opencv_contrib.git

For an older version of OpenCV, cd to both opencv and opencv_contrib directories and run git checkout <opencv-version>

Once done, create a temporary build directory and navigate to it:

$ cd ~/opencv_build/opencv
$ mkdir -p build && cd build

iii. Set up the OpenCV build with CMake:

$ cmake -D CMAKE_BUILD_TYPE=RELEASE \
-D CMAKE_INSTALL_PREFIX=/usr/local \
-D INSTALL_C_EXAMPLES=ON \
-D INSTALL_PYTHON_EXAMPLES=ON \
-D OPENCV_GENERATE_PKGCONFIG=ON \
-D OPENCV_EXTRA_MODULES_PATH=~/opencv_build/opencv_contrib/modules \
-D BUILD_EXAMPLES=ON ..

Output:

— Configuring done
— Generating done
— Build files have been written to: /home/vagrant/opencv_build/opencv/build

iv. Start the compilation process:

$ make -j8

Initially, we modify the -j flag according to the processor. To find the number of cores in the processor, type nproc.

Wait for the compilation to finish.

v. Install OpenCV:

$ sudo make install

In order to verify, type the following commands.

C++ bindings:

$ pkg-config –modversion opencv4

Output:

4.3.0

Python bindings:

python3 -c “import cv2; print(cv2.__version__)”

Output

4.3.0-dev

3. Pip Install OpenCV For Desktop Environments

To install OpenCV, run:

$ pip3 install opencv-python
$ sudo pip3 install scikit-build
$ sudo pip3 install cmake
$ sudo pip3 install opencv-python

open-cv python will install only main modules. However, to install both main and contrib modules, run:

$ sudo pip3 install opencv-contrib-python

4. Pip install OpenCV For Server (headless) Environments

To install for headless environments where there is no GUI available, run:

For main modules only:

$ sudo pip3 install opencv-python-headless

For both main and contrib modules:

$ sudo pip3 install opencv-contrib-python-headless

To verify installation, invoke Python3 console and run:

$ import csv2

How to fix Error encountered while installing OpenCV on Ubuntu 20.04 ?

While installing OpenCV one of our customers came across the following error:

Error: ModuleNotFoundError: No module named ‘skbuild’

In order to resolve this, we make sure that Pip is the latest.

If not, update Pip.

Eventually run the following commands:

$ sudo pip3 install scikit-build
$ sudo pip3 install cmake
$ sudo pip3 install opencv-python