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opencv/doc/tutorials/introduction/general_install/general_install.markdown
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Merge pull request #18195 from mshabunin:linux-tutorial 
Installation tutorials rework

* Doc: general installation, config reference, linux installation

* Doc: addressed review comments

* Minor fixes
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OpenCV installation overview

@tableofcontents

There are two ways of installing OpenCV on your machine: download prebuilt version for your platform or compile from sources.

Prebuilt version

In many cases you can find prebuilt version of OpenCV that will meet your needs.

Packages by OpenCV core team

Packages for Android, iOS and Windows built with default parameters and recent compilers are published for each release, they do not contain opencv_contrib modules.

Third-party packages

Other organizations and people maintain their own binary distributions of OpenCV. For example:

Build from sources

It can happen that existing binary packages are not applicable for your use case, then you'll have to build custom version of OpenCV by yourself. This section gives a high-level overview of the build process, check tutorial for specific platform for actual build instructions.

OpenCV uses CMake build management system for configuration and build, so this section mostly describes generalized process of building software with CMake.

Step 0: Prerequisites

Install C++ compiler and build tools. On *NIX platforms it is usually GCC/G++ or Clang compiler and Make or Ninja build tool. On Windows it can be Visual Studio IDE or MinGW-w64 compiler. Native toolchains for Android are provided in the Android NDK. XCode IDE is used to build software for OSX and iOS platforms.

Install CMake from the official site or some other source.

Get other third-party dependencies: libraries with extra functionality like decoding videos or showing GUI elements; libraries providing optimized implementations of selected algorithms; tools used for documentation generation and other extras. Check @ref tutorial_config_reference for available options and corresponding dependencies.

Step 1: Get software sources

Typical software project consists of one or several code repositories. OpenCV have two repositories with code: opencv - main repository with stable and actively supported algorithms and opencv_contrib which contains experimental and non-free (patented) algorithms; and one repository with test data: opencv_extra.

You can download a snapshot of repository in form of an archive or clone repository with full history.

To download snapshot archives:

To clone repositories run the following commands in console (git must be installed):

git clone https://github.com/opencv/opencv
git -C opencv checkout <some-tag>

# optionally
git clone https://github.com/opencv/opencv_contrib
git -C opencv_contrib checkout <same-tag-as-opencv>

# optionally
git clone https://github.com/opencv/opencv_extra
git -C opencv_extra checkout <same-tag-as-opencv>

@note If you want to build software using more than one repository, make sure all components are compatible with each other. For OpenCV it means that opencv and opencv_contrib repositories must be checked out at the same tag or that all snapshot archives are downloaded from the same release.

@note When choosing which version to download take in account your target platform and development tools versions, latest versions of OpenCV can have build problems with very old compilers and vice versa. We recommend using latest release and fresh OS/compiler combination.

Step 2: Configure

At this step CMake will verify that all necessary tools and dependencies are available and compatible with the library and will generate intermediate files for the chosen build system. It could be Makefiles, IDE projects and solutions, etc. Usually this step is performed in newly created build directory:

cmake -G<generator> <configuration-options> <source-directory>

@note cmake-gui application allows to see and modify available options using graphical user interface. See https://cmake.org/runningcmake/ for details.

Step 3: Build

During build process source files are compiled into object files which are linked together or otherwise combined into libraries and applications. This step can be run using universal command:

cmake --build <build-directory> <build-options>

... or underlying build system can be called directly:

make

Step 3: Install

During installation procedure build results and other files from build directory will be copied to the install location. Default installation location is /usr/local on UNIX and C:/Program Files on Windows. This location can be changed at the configuration step by setting CMAKE_INSTALL_PREFIX option. To perform installation run the following command:

cmake --build <build-directory> --target install <other-options>

@note This step is optional, OpenCV can be used directly from the build directory.

@note If the installation root location is a protected system directory, so the installation process must be run with superuser or administrator privileges (e.g. sudo cmake ...).