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OpenEXR is a high dynamic-range (HDR) image file format developed by Industrial Light & Magic for use in computer imaging applications
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OpenEXR is a high dynamic-range (HDR) image file format developed by Industrial Light & Magic (ILM) for use in computer imaging applications. ILM subsequently released the source code and adjoining material as open source software.

The distribution has evolved to include support for stereoscopic and deep images. Weta Digital, Disney, Sony Pictures Imageworks, Pixar, DreamWorks Animation and other studios have made contributions to the code base. The file format has seen wide adoption in a number of industries.

The library, including all contributions, is released under the modified BSD license.

OpenEXR's features include:

  • Higher dynamic range and color precision than existing 8- and 10-bit image file formats.
  • Support for 16-bit floating-point, 32-bit floating-point, and 32-bit integer pixels. The 16-bit floating-point format, called "half", is compatible with the half data type in NVIDIA's Cg graphics language and is supported natively on their GPUs.
  • Multiple image compression algorithms, both lossless and lossy. Some of the included codecs can achieve 2:1 lossless compression ratios on images with film grain. The lossy codecs have been tuned for visual quality and decoding performance.
  • Extensibility. New compression codecs and image types can easily be added by extending the C++ classes included in the OpenEXR software distribution. New image attributes (strings, vectors, integers, etc.) can be added to OpenEXR image headers without affecting backward compatibility with existing OpenEXR applications.
  • Support for sterescopic image workflows and a generalization to multi-views.

Added Feature highlights for v2 release

  • Flexible support for deep data: pixels can store a variable-length list of samples and, thus, it is possible to store multiple values at different depths for each pixel. Hard surfaces and volumetric data representations are accomodated.
  • Multipart: ability to encode separate, but related, images in one file. This allows for access to individual parts without the need to read other parts in the file.
  • Versioning: OpenEXR source allows for user configurable C++ namespaces to provide protection when using multiple versions of the library in the same process space.


The distribution is divided into the following sub-modules:

  • IlmBase
  • OpenEXR
  • OpenEXR_Viewers
  • PyIlmBase
  • Contrib

Please see the README files of each of the individual directories for more information.

A collection of OpenEXR images is available from the adjacent repository openexr-images.

Building with CMake

To build with CMake, OpenEXR has a few prerequisites.

  • CMake 3.11 or newer
  • zlib
  • boost-python (if the python bindings are to be built)
  • fltk (if the openexr viewer is to be built)
  • Cg (if playexr is to be built)

When these prerequisites are fulfulled, prepare the build environment.

In the root CMakeLists.txt file, or using a tools such as ccmake or cmake-gui, configure the OpenEXR build. The options are detailed below.

Create a build directory, cd into it, and run cmake to configure the build. Select an appropriate generator, such as "Unix Makefiles", or "Visual Studio 15 2017 Win64".

cmake -DCMAKE_INSTALL_PREFIX=<install location> <OpenEXR source root> -G "selected generator" -DCMAKE_PREFIX_PATH=<paths to dependencies - zlib etc>

The available options are:

  • OPENEXR_BUILD_ILMBASE (ON) By default, IlmBase is always built.

  • OPENEXR_BUILD_OPENEXR (ON) By default, OpenEXR is always built.

  • OPENEXR_BUILD_PYTHON_LIBS (ON) By default, the Python bindings will be built.

  • OPENEXR_BUILD_VIEWERS (OFF) By default, the viewers are not built, as they have not been updated for modern OpenGL.


  • OPENEXR_BUILD_STATIC (OFF) The build can be configured to create either shared libraries, or static libraries, or both.

  • OPENEXR_NAMESPACE_VERSIONING (ON) OpenEXR symbols will be contained within a namespace

  • OPENEXR_FORCE_CXX03 (OFF) C++03 compatibility is possible as an option

  • OPENEXR_ENABLE_TESTS (ON) By default, the tests will be built.

  • OPENEXR_PYTHON_MAJOR, OPENEXR_PYTHON_MINOR "2", "7" By default, OpenEXR is built against Python 2.7.x.

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