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OpenCV
4.5.3
Open Source Computer Vision
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OpenCV
4.5.3
Open Source Computer Vision
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Next Tutorial: OpenCV configuration options reference
There are two ways of installing OpenCV on your machine: download prebuilt version for your platform or compile from sources.
In many cases you can find prebuilt version of OpenCV that will meet your needs.
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.
Other organizations and people maintain their own binary distributions of OpenCV. For example:
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.
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 OpenCV configuration options reference for available options and corresponding dependencies.
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):
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-gui application allows to see and modify available options using graphical user interface. See https://cmake.org/runningcmake/ for details.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:
... or underlying build system can be called directly:
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:
sudo cmake ...).It is possible to decouple some of OpenCV dependencies and make them optional by extracting parts of the code into dynamically-loaded plugins. It helps to produce adaptive binary distributions which can work on systems with less dependencies and extend functionality just by installing missing libraries. For now modules core, videoio and highgui support this mechanism for some of their dependencies. In some cases it is possible to build plugins together with OpenCV by setting options like VIDEOIO_PLUGIN_LIST or HIGHGUI_PLUGIN_LIST, more options related to this scenario can be found in the OpenCV configuration options reference. In other cases plugins should be built separately in their own build procedure and this section describes such standalone build process.
Build procedure is similar to the main OpenCV build, but you have to use special CMake projects located in corresponding subdirectories, these folders can also contain reference scripts and Docker images. It is important to use opencv_<module>_<backend> name prefix for plugins so that loader is able to find them. Each supported prefix can be used to load only one library, however multiple candidates can be probed for a single prefix. For example, you can have libopencv_videoio_ffmpeg_3.so and libopencv_videoio_ffmpeg_4.so plugins and the first one which can be loaded successfully will occupy internal slot and stop probing process. Possible prefixes and project locations are presented in the table below:
| module | backends | location |
|---|---|---|
| core | parallel_tbb, parallel_onetbb, parallel_openmp | opencv/modules/core/misc/plugins |
| highgui | gtk, gtk2, gtk3 | opencv/modules/highgui/misc/plugins |
| videoio | ffmpeg, gstreamer, intel_mfx, msmf | opencv/modules/videoio/misc |
Example:
OpenCV_DIR environment or CMake variable to the directory with OpenCVConfig.cmake file, it can be OpenCV build directory or some path in the location where you performed installation. 
1.8.13