The OpenEXR library is available for download and installation in binary form via package managers on many Linux distributions. See for a complete list.


% sudo yum makecache
% sudo yum install OpenEXR


% sudo apt-get update
% sudo apt-get install openexr

Beware that some distributions are out of date and only provide distributions of outdated releases OpenEXR. We recommend against using OpenEXR v2, and we strongly recommend against using OpenEXR v1.

On macOS, install via Homebrew:

% brew install openexr

We do not recommend installation via Macports because the distribution is out of date.

Also note that the official OpenEXR project does not provide supported python bindings. pip install openexr installs the openexrpython module, which is not affiliated with the OpenEXR project or the ASWF. Please direct questions there.

Build from Source

OpenEXR builds on Linux, macOS, Microsoft Windows via CMake, and is cross-compilable on other systems.

Download the source from the GitHub releases page page, or clone the repo.

The release branch of the repo always points to the most advanced release.


Make sure these are installed on your system before building OpenEXR:

The instructions that follow describe building OpenEXR with CMake.

Note that as of OpenEXR 3, the Gnu autoconf bootstrap/configure build system is no longer supported.


To build via CMake, you need to first identify three directories:

  1. The source directory, i.e. the top-level directory of the downloaded source archive or cloned repo, referred to below as $srcdir

  2. A temporary directory to hold the build artifacts, referred to below as $builddir

  3. A destination directory into which to install the libraries and headers, referred to below as $installdir.

To build:

% cd $builddir
% cmake $srcdir --install-prefix $installdir
% cmake --build $builddir --target install --config Release

Note that the CMake configuration prefers to apply an out-of-tree build process, since there may be multiple build configurations (i.e. debug and release), one per folder, all pointing at once source tree, hence the $builddir noted above, referred to in CMake parlance as the build directory. You can place this directory wherever you like.

See the CMake Configuration Options section below for the most common configuration options especially the install directory. Note that with no arguments, as above, make install installs the header files in /usr/local/include, the object libraries in /usr/local/lib, and the executable programs in /usr/local/bin.


Under Windows, if you are using a command line-based setup, such as cygwin, you can of course follow the above. For Visual Studio, cmake generators are “multiple configuration”, so you don’t even have to set the build type, although you will most likely need to specify the install location. Install Directory By default, make install installs the headers, libraries, and programs into /usr/local, but you can specify a local install directory to cmake via the CMAKE_INSTALL_PREFIX variable:

% cmake .. -DCMAKE_INSTALL_PREFIX=$openexr_install_directory

Library Names

By default, libraries are installed with the following names/symlinks: ->$SOVERSION ->$SOVERSION.$RELEASE$SOVERSION.$RELEASE (the shared object file)

The SOVERSION number identifies the ABI version. Each OpenEXR release that changes the ABI in backwards-incompatible ways increases this number. By policy, this changes only for major and minor releases, never for patch releases. RELEASE is the MAJOR.MINOR.PATCH release name. For example, the resulting shared library filename is for OpenEXR release v3.2.0. This naming scheme reinforces the correspondence between the real filename of the .so and the release it corresponds to.

Library Suffix

The OPENEXR_LIB_SUFFIX CMake option designates a suffix for the library and appears between the library base name and the .so. This defaults to encode the major and minor version, as in -3_1: -> -> -> (the shared object file)

Imath Dependency

OpenEXR depends on Imath. If a suitable installation of Imath cannot be found, CMake will automatically download it at configuration time. To link against an existing installation of Imath, add the Imath directory to the CMAKE_PREFIX_PATH setting:

% mkdir $build_directory
% cd $build_directory
% cmake -DCMAKE_PREFIX_PATH=$imath_install_directory \
        -DCMAKE_INSTALL_PREFIX=$openexr_install_destination \
% cmake --build . --target install --config Release

Alternatively, you can specify the Imath_DIR variable:

% mkdir $build_directory
% cd $build_directory
% cmake -DImath_DIR=$imath_config_directory \
        -DCMAKE_INSTALL_PREFIX=$openexr_install_destination \
% cmake --build . --target install --config Release

Note that Imath_DIR should point to the directory that includes the ImathConfig.cmake file, which is typically the lib/cmake/Imath folder of the root install directory where Imath is installed.

See below for other customization options.

Porting Applications from OpenEXR v2 to v3

See the OpenEXR/Imath 2.x to 3.x Porting Guide for details about differences from previous releases and how to address them. Also refer to the porting guide for details about changes to Imath.

Building the Website

The website is generated via Sphinx with the Breathe extension, using the sphinx-press-theme, and is hosted by readthedocs. The website source is in restructured text in the website directory.

To build the website locally from the source .rst files, set the CMake option BUILD_WEBSITE=ON. This adds the website CMake target. Generation is off by default.

Building the website requires that sphinx, breathe, and doxygen are installed. It further requires the sphinx-press-theme. Complete dependencies are described in the requirements.txt file. Furthermore, building the website from source requires the Imagemagick convert utility, which processes exr files from for the example image gallery.

On Debian/Ubuntu Linux:

% apt-get install doxygen python3-sphinx imagemagick
% pip3 install breathe
% pip3 install sphinx_press_theme

% mkdir _build
% cd _build
% cmake --build . --target website

CMake Build-time Configuration Options

The default CMake configuration options are stored in cmake/OpenEXRSetup.cmake. To see a complete set of option variables, run:

% cmake -LAH $openexr_source_directory

You can customize these options three ways:

  1. Modify the .cmake files in place.

  2. Use the UI cmake-gui or ccmake.

  3. Specify them as command-line arguments when you invoke cmake.

Library Naming Options


    Append the given string to the end of all the OpenEXR libraries. Default is -<major>_<minor> version string. Please see the section on library names

Imath Dependency


    The standard CMake path in which to search for dependencies, Imath in particular. A comma-separated path. Add the root directory where Imath is installed.

  • Imath_DIR

    The config directory where Imath is installed. An alternative to using CMAKE_PREFIX_PATH. Note that Imath_DIR should be set to the directory that includes the ImathConfig.cmake file, which is typically the lib/cmake/Imath folder of the root install directory.


    The github Imath repo to auto-fetch if an installed library cannot be found, and the tag to sync it to. The default repo is and the tag is specific to the OpenEXR release. The internal build is configured as a CMake subproject.


    If set to ON, force auto-fetching and internal building of Imath using OPENEXR_IMATH_REPO and OPENEXR_IMATH_TAG. This means do not use any existing installation of Imath.

libdeflate Dependency

As of OpenEXR release v3.2, OpenEXR depends on libdeflate for DEFLATE-based compression. Previous OpenEXR releases relied on zlib. Builds of OpenEXR can choose either an libdeflate installation, or CMake can auto-fetch the source and build it internally. The internal build is linked statically, so no extra shared object is produced.


    The github Imath repo to auto-fetch if an installed library cannot be found, and the tag to sync it to. The default repo is and the tag is v1.18. The internal build is configured as a CMake subproject.


    If set to ON, force auto-fetching and internal building of libdeflate using OPENEXR_DEFLATE_REPO and OPENEXR_DEFLATE_TAG. This means do not use any existing installation of libdeflate.

Test Images Dependency

The OpenEXR test suite relies on images from the online test image gallery, which CMake automatically downloads during configuration. You can provide an alternate location for the test images via the OPENEXR_IMAGES_REPO and OPENEXR_IMAGES_TAG variables.


    The images repo to auto-fetch for the test suite, and the tag to sync it to. The default repo is and the tag is v1.0.

Note that you can void downloading images by specifying a repo on the local filesystem via a file: url:

cmake -DOPENEXR_IMAGES_REPO=file:///my/clone/of/openexr-images -DOPENEXR_IMAGES_TAG=""

Namespace Options


    Public namespace alias for OpenEXR. Default is Imf.


    Real namespace for OpenEXR that will end up in compiled symbols. Default is Imf_<major>_<minor>.


    Whether the namespace has been customized (so external users know)


    Public namespace alias for Iex. Default is Iex.


    Real namespace for Iex that will end up in compiled symbols. Default is Iex_<major>_<minor>.


    Whether the namespace has been customized (so external users know)


    Public namespace alias for IlmThread. Default is IlmThread.


    Real namespace for IlmThread that will end up in compiled symbols. Default is IlmThread_<major>_<minor>.


    Whether the namespace has been customized (so external users know)

Component Options


    Build the testing tree. Default is ON. Note that this causes the test suite to be compiled, but it is not executed. To execute the suite, run “make test”.


    Controls whether to include the fuzz tests (very slow). Default is OFF.


    Build and install the binary programs (exrheader, exrinfo, exrmakepreview, etc). Default is ON.


    Build and install the example code. Default is ON.

Additional CMake Options

See the CMake documentation for more information (


    For builds when not using a multi-configuration generator. Available values: Debug, Release, RelWithDebInfo, MinSizeRel


    This is the primary control whether to build static libraries or shared libraries / dlls (side note: technically a convention, hence not an official CMAKE_ variable, it is defined within cmake and used everywhere to control this static / shared behavior)


    C++ standard to compile against. This obeys the global CMAKE_CXX_STANDARD but doesn’t force the global setting to enable sub-project inclusion. Default is 14.


    The C++ compiler.


    The C compiler.


    For non-standard install locations where you don’t want to have to set LD_LIBRARY_PATH to use them


    Enable/Disable output of compile commands during generation. Default is OFF.


    Echo all compile commands during make. Default is OFF.

Cross Compiling / Specifying Specific Compilers

When trying to either cross-compile for a different platform, or for tasks such as specifying a compiler set to match the VFX reference platform, cmake provides the idea of a toolchain which may be useful instead of having to remember a chain of configuration options. It also means that platform-specific compiler names and options are out of the main cmake file, providing better isolation.

A toolchain file is simply just a cmake script that sets all the compiler and related flags and is run very early in the configuration step to be able to set all the compiler options and such for the discovery that cmake performs automatically. These options can be set on the command line still if that is clearer, but a theoretical toolchain file for compiling for VFX Platform 2015 is provided in the source tree at cmake/Toolchain-Linux-VFX_Platform15.cmake which will hopefully provide a guide how this might work.

For cross-compiling for additional platforms, there is also an included sample script in cmake/Toolchain-mingw.cmake which shows how cross compiling from Linux for Windows may work. The compiler names and paths may need to be changed for your environment.

More documentation:


If you have Ninja installed, it is faster than make. You can generate ninja files using cmake when doing the initial generation:

% cmake -G “Ninja” ..