The Imath library is available for download and installation in binary form via package managers on many Linux distributions.

Refer to the current version of Imath on various major Linux distros at

Older versions of Imath were distributed as a component of OpenEXR called ilmbase. We do not recommend using these outdated versions.

To install via yum on RHEL/CentOS:

% sudo yum makecache
% sudo yum install imath

To install via apt-get on Ubuntu:

% sudo apt-get update
% sudo apt-get install imath


On macOS, install via Homebrew:

% brew install imath

Alternatively, you can install on macOS via MacPorts:

% port install imath


Install via vcpkg:

% .\vcpkg install imath


Please note that pip install imath installs the imath module, which is not affiliated with the OpenEXR project or the ASWF. Please direct questions there.

Build from Source

Imath 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 Imath:

  • Imath requires CMake version 3.14 or newer

  • C++ compiler that supports C++11

The instructions that follow describe building Imath with CMake.


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=$Imath_install_directory

Library Names

By default the installed libraries follow a pattern for how they are named. This is done to enable multiple versions of the library to be installed and targeted by different builds depending on the needs of the project. A simple example of this would be to have different versions of the library installed to allow for applications targeting different VFX Platform years to co-exist.

If you are building dynamic libraries, once you have configured, built, and installed the libraries, you should see the following pattern of symlinks and files in the install lib folder: ->$SOVERSION ->$SOVERSION.$RELEASE$SOVERSION.$RELEASE (the shared object file)

The SOVERSION number identifies the ABI version. Each Imath 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 Imath release v3.1.10. This naming scheme reinforces the correspondence between the real filename of the .so and the release it corresponds to.

Library Suffix

The IMATH_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)

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 Imath technical documentation at is generated via Sphinx with the Breathe extension using information extracted from header comments by Doxygen, using the sphinx-press-theme, and is hosted by Read the Docs. The website source is in restructured text in the website directory.

To build the website locally from the source headers and .rst files, set the CMake option BUILD_WEBSITE=ON. This adds 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.

On Debian/Ubuntu Linux:

% apt-get install doxygen python3-sphinx
% 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/ImathSetup.cmake. To see a complete set of option variables, run:

% cmake -LAH $imath_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 Imath 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.

Namespace Options


    Public namespace alias for Imath. Default is Imath.


    Real namespace for Imath that will end up in compiled symbols. Default is Imath_<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”.

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” ..