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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.

OpenEXR is used by ILM on all motion pictures currently in production. The first movies to employ OpenEXR were Harry Potter and the Sorcerers Stone, Men in Black II, Gangs of New York, and Signs. Since then, OpenEXR has become ILM's main image file format.

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 new GeForce FX and Quadro FX 3D graphics solutions.
  • 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.
  • Deep Data. Pixels can store a variable length list of samples. The main rationale behind deep-images is to store multiple values at different depths for each pixel. Support for hard surface and volumetric representation requirements for deep compositing workflows.
  • Multi-part image files. Files can contain a number of separate, but related, images in one file. Access to any part is independent of the others; in particular, no access of data need take place for unrequested parts.

ILM has released OpenEXR as free software. The OpenEXR software distribution includes:

  • IlmImf, a library that reads and writes OpenEXR images.
  • IlmImfUtil, a convenience library to simplify development of OpenEXR utilities.
  • Half, a C++ class for manipulating half values as if they were a built-in C++ data type.
  • Imath, a math library with support for matrices, 2d- and 3d-transformations, solvers for linear/quadratic/cubic equations, and more.
  • exrdisplay, a sample application for viewing OpenEXR images on a display at various exposure settings.

The OpenEXR software distribution is now licensed under the modified BSD license, available here.

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August 10, 2014 - OpenEXR v2.2.0 has been released and is available for download. This release includes the following components:

  • OpenEXR: v2.2.0
  • IlmBase: v2.2.0
  • PyIlmBase: v2.2.0
  • OpenEXR_Viewers: v2.2.0

This significant new features of this release include:

  • DreamWorks Lossy Compression A new high quality, high performance lossy compression codec contributed by DreamWorks Animation. This codec allows control over variable lossiness to balance visual quality and file size. This contribution also includes performance improvements that speed up the PIZ codec.
  • IlmImfUtil A new library intended to aid in development of image file manipulation utilities that support the many types of OpenEXR images.
  • This release also includes improvements to cross-platform build support using CMake.

    OpenEXR source can be obtained from the downloads section of www.openexr.com or from the project page on github: https://github.com/openexr/openexr

    November 25, 2013 - OpenEXR v2.1.0 has been released and is available for download. This release includes the following components (version locked):

    • OpenEXR: v2.1.0
    • IlmBase: v2.1.0
    • PyIlmBase: v2.1.0
    • OpenEXR_Viewers: v2.1.0

    This release includes a refactoring of the optimised read paths for RGBA data, optimisations for some of the python bindings to Imath, improvements to the cmake build environment as well as additional documentation describing deep data in more detail.

    April 9, 2013 - Industrial Light & Magic (ILM) and Weta Digital announce the release of OpenEXR 2.0, the major version update of the open source high dynamic range file format first introduced by ILM and maintained and expanded by a number of key industry leaders including Weta Digital, Pixar Animation Studios, Autodesk and others.

    The release includes a number of new features that align with the major version number increase. Amongst the major improvements are:

    1. Deep Data support - Pixels can now store a variable-length list of samples. The main rationale behind deep images is to enable the storage of multiple values at different depths for each pixel. OpenEXR 2.0 supports both hard-surface and volumetric representations for Deep Compositing workflows.
    2. Multi-part Image Files - With OpenEXR 2.0, files can now contain a number of separate, but related, data parts in one file. Access to any part is independent of the others, pixels from parts that are not required in the current operation don't need to be accessed, resulting in quicker read times when accessing only a subset of channels. The multipart interface also incorporates support for Stereo images where views are stored in separate parts. This makes stereo OpenEXR 2.0 files significantly faster to work with than the previous multiview support in OpenEXR.
    3. Optimized pixel reading - decoding RGB(A) scanline images has been accelerated on SSE processors providing a significant speedup when reading both old and new format images, including multipart and multiview files.
    4. Namespacing - The library introduces versioned namespaces to avoid conflicts between packages compiled with different versions of the library.

    Although OpenEXR 2.0 is a major version update, files created by the new library that don't exercise the new feature set are completely backwards compatible with previous versions of the library. By using the OpenEXR 2.0 library, performance improvements, namespace versions and basic multi-part/deep reading support should be available to applications without code modifications.

    This code is designed to support Deep Compositing - a revolutionary compositing workflow developed at Weta Digital that detached the rendering of different elements in scene. In particular, changes in one layer could be rendered separately without the need to re-render other layers that would be required to handle holdouts in a traditional comp workflow or sorting of layers in complex scenes with elements moving in depth. Deep Compositing became the primary compositing workflow on Avatar and has seen wide industry adoption. The technique allows depth and color value to be stored for every pixel in a scene allowing for much more efficient handling of large complex scenes and greater freedom for artists to iterate.

    True to the open source ethos, a number of companies contributed to support the format and encourage adoption. Amongst others, Pixar Animation Studios has contributed its DtexToExr converter to the OpenEXR repository under a Microsoft Public License, which clears any concerns about existing patents in the area, and Autodesk provided performance optimizations geared towards real-time post-production workflows.

    Extensive effort has been put in ensuring all requirements were met to help a wide adoption, staying true to the wide success of OpenEXR. Many software companies were involved in the beta cycle to insure support amongst a number of industry leading applications. Numerous packages like SideFX's Houdini, Autodesk's Maya, Solid Angle's Arnold renderer, Sony Pictures Imageworks' Open Image IO have already announced their support of the format.

    Open EXR 2.0 is an important step in the adoption of deep compositing as it provides a consistent file format for deep data that is easy to read and work with throughout a visual effects pipeline. The Foundry has build OpenEXR 2.0 support into its Nuke Compositing application as the base for the Deep Compositing workflows.

    OpenEXR 2.0 is already in use at both Weta Digital and Industrial Light & Magic. ILM took advantage of the new format on Marvel's The Avengers and two highly anticipated summer 2013 releases, Pacific Rim and The Lone Ranger. Recent examples of Weta Digital's use of the format also include Marvel's Avengers as well as Prometheus and The Hobbit. In addition, a large number of visual effects studios have already integrated a deep workflow into their compositing pipelines or are in the process of doing so including:, Sony Pictures Imageworks, Pixar Animation Studios, Rhythm & Hues, Fuel and MPC.

    In addition to visual effects, the new additions to the format, means that depth data can also be assigned to two-dimensional data for a use in many design fields including, architecture, graphic design, automotive and product prototyping.


    July 31st, 2012 - OpenEXR v1.7.1 has been released and is available for download. This release includes the following components:

    • OpenEXR: v1.7.1
    • IlmBase: v1.0.3
    • PyIlmBase: v1.0.0 (introduces a Boost dependency)
    • OpenEXR_Viewers: v1.0.2

    Of particular note is the introduction of PyIlmBase. This module forms a comprehensive set of python bindings to the IlmBase module.

    In addition, contained in this release is a number of additions to Imath as well as a minor tweak to Imath::Frustrum (for better support for Windows platforms) as well as other minor fixes, including correction for soname version of IlmImf.


    June 18, 2012 - We're pleased to announce the first public Beta release of OpenEXR v2.

    Development of OpenEXR v2 has been undertaken in a collaborative environment (cf. previous github announcement) comprised of Industrial Light & Magic, Weta Digital as well as a number of other contributors.

    Some of the new features included in the Beta.1 release of OpenEXR v2 are:

    * Deep Data. Pixels can now store a variable length list of samples. The main rationale behind deep-images is to have multiple values at different depths for each pixel. OpenEXR v2 supports both hard surface and volumetric representation requirements for deep compositing workflows.

    * Multi-part image files. With OpenEXR v2, files can now contain a number of separate, but related, images in one file. Access to any part is independent of the others; in particular, no access of data need take place for unrequested parts.

    In addition, OpenEXR v2 also contains platform independent mechanisms for handling co-existing library version conflicts in the same process space. (Currently implemented in IlmImf)

    Finally, a reminder that this is a Beta release and potentially incompatible changes may be introduced in future releases prior to the v2.0.0 production version.

    OpenEXR v2Beta.1 can be found at: https://github.com/openexr/openexr/tree/v2_beta.1


    June 18, 2012 - We're pleased to announce that the OpenEXR source code is moving to github.com. You can browse, download and branch the code at www.github.com/openexr/openexr.

    We're looking forward to taking advantage of the collaborative features presented by git and github.com and of course community contributions. Please see the developer Wiki pages for more information regarding participation.


    July 23, 2010 - New feature version of OpenEXR is now available. This release includes support for stereoscopic images, please see the adjoining documentation in the MultiViewOpenEXR.pdf. (Many thanks to Weta Digital for their contribution.) In addition, we added support for targeting 64 bit Windows, fixes for buffer overruns and a number of other minor fixes, additions and optimisations. Please see the Changelog files for more detailed information.

    OpenEXR 1.7.0, OpenEXR_Viewers 1.0.2, IlmBase 1.0.2 and OpenEXR-Images-1.7.0 can be downloaded from the downloads section of www.openexr.com


    October 22, 2007 - New versions of OpenEXR and CTL are now available. This release fixes a buffer overrun in OpenEXR and a Windows build problem in CTL, and it removes a few unnecessary files from the .tar.gz packages.

    OpenEXR 1.6.1, OpenEXR_Viewers 1.0.1 and IlmBase 1.0.1 can be downloaded from the downloads section of www.openexr.com. CTL 1.4.1 and OpenEXR_CTL 1.0.1 can be downloaded from http://www.oscars.org/science-technology/council/projects/ctl.html.


    August 3, 2007 - New stable versions of OpenEXR and CTL are now available. The source code has been tested on Linux, Mac OS X and Windows (Visual Studio 7 and 8).

    Here's a summary of what has changed since the last release:

    OpenEXR 1.6.0

    • Reduced generational loss in B44- and B44A-compressed images.
    • Added B44A compression. This is a variation of B44, but with a better compression ratio for images with large uniform areas, such as in an alpha channel.
    • Bug fixes.

    CTL 1.4.0

    • Added new functions to the CTL standard library: 3x3 matrix support, 1D lookup tables with cubic interpolation.
    • Added new "ctlversion" statement to the language.
    • Bug fixes.

    OpenEXR_CTL 1.0.0

    • Applying CTL transforms to a frame buffer is multi-threaded.
    • Bug fixes.

    OpenEXR_Viewers 1.0.0

    • Implemented new naming conventions for CTL parameters.

    IlmBase 1.0.0

    • Half now implements "round to nearest even" mode.

    OpenEXR 1.6.0, OpenEXR_Viewers 1.0.0 and IlmBase 1.0.0 can be downloaded from the downloads section of www.openexr.com. CTL 1.4.0 and OpenEXR_CTL 1.0.0 can be downloaded from http://www.oscars.org/council/ctl.html.


    January 22, 2007 - CTL has been released.

    The Color Transformation Language, or CTL, is a programming language for digital color management. Color management requires translating images between different representations or color spaces. CTL allows users to describe color transforms in a concise and unambiguous way by expressing them as programs. In order to apply a given transform to an image, a color management system instructs a CTL interpreter to load and run the CTL program that describes the transform.

    The image viewers included in the OpenEXR software distribution, exrdisplay and playexr, both support color rendering via CTL. For more information see http://www.openexr.com/OpenEXRViewers.pdf.

    Sorce code and documentation for the CTL interpreter can be downloaded from http://ampasctl.sourceforge.net. Please note the license under which CTL is distributed; it is similar but not identical to the OpenEXR license.


    January 4, 2007 - OpenEXR wins an Academy Award for Technical Achievement.

    The Academy of Motion Picture Arts and Sciences today announced the 15 winners of Scientific and Technical Academy Awards. A Technical Achievement Award goes to Florian Kainz for the design and engineering of OpenEXR, a software package implementing 16-bit, floating-point, high dynamic range image files. Widely adopted, OpenEXR is engineered to meet the requirements of the visual effects industry by providing for lossless and lossy compression of tiered and tiled images.

    Congratulations to all for making OpenEXR such a success!!!

    Click here for the official Press Release


    December 15, 2006 - A new development version of OpenEXR is now available. We have tested the code in this version internally at ILM, but we would like to get feedback from others before we release a production version.

    The new version includes several significant changes:

    • OpenEXR supports a new image compression method, called B44. It has a fixed compression rate of 2.28:1, or 4.57:1 if used in combination with luminance/chroma encoding. B44-compressed images can be uncompressed fast enough to support real-time playback of image sequences.
    • The new playexr program plays back moving image sequences. Playexr is multi-threaded and utilizes the threading capabilities of the IlmImf library that were introduced in OpenEXR 1.3.0. The program plays back B44-compressed images with fairly high-resolution in real time on commodity hardware.
    • The playexr program and a new version of the existing exrdisplay image viewer both support color rendering via color transforms written in the new Color Transformation Language or CTL. CTL is not part of OpenEXR; it will be released separately. CTL support in playexr and exrdisplay is optional; the programs can be built and will run without CTL.
    • In preparation for the release of CTL, OpenEXR has been split into three separate packages:
      • IlmBase 0.9.0 includes the Half, Iex, Imath and IlmThread libraries
      • OpenEXR 1.5.0 includes the IlmImf library, programming examples and utility programs such as exrheader or exrenvmap
      • OpenEXRViewers 0.9.0 includes the playexr and exrdisplay programs
    • The "Technical Introduction to OpenEXR" document now includes a recommendation for storing CIE XYZ pixel data in OpenEXR files.
    • A new "OpenEXR Image Viewing Software" document describes the playexr and exrdisplay programs. It briefly explains real-time playback and color rendering, and includes recommendations for testing if other image viewing software displays OpenEXR images correctly.
    • The OpenEXR sample image set now includes B44-compressed files and files with CIE XYZ pixel data.


    August 8, 2006 - We have released an updated set of sample OpenEXR images. This release includes several new images that are useful for testing OpenEXR applications. The images are organized by subdirectory according to their image type or purpose. Several of these subdirectories contain README files that explain the contents of the images in those subdirectories.


    August 2, 2006 - OpenEXR 1.4.0 is now available. This is the next major production-ready release of OpenEXR and offers full compatibility with our last production release, which was 1.2.2. This version obsoletes versions 1.3.x, which were test versions for 1.4.0. If you have been using 1.3.x, please upgrade to 1.4.0.


    June 8, 2006 - OpenEXR 1.3.0 is now available. This is a test release. The major new feature in this version is support for multithreaded file I/O. We've been testing the threaded code internally at ILM for a few months, and we have not encountered any bugs, but we'd like to get some feedback from others before we release the production version.

    Here's a summary of the changes since version 1.2.2:

    • Support for multithreaded file reading and writing.
    • Support for Intel-based OS X systems.
    • Support for Visual Studio 2005.
    • Better handling of PLATFORM_* and HAVE_* macros.
    • Updated documentation.
    • Bug fixes related to handling of incomplete and damaged files.
    • Numerous bug fixes and cleanups to the autoconf-based build system.
    • Removed support for the following configurations that were previously supported. Some of these configurations may happen to continue to function, but we can't help you if they don't, largely because we don't have any way to test them:

      • IRIX
      • OSF1
      • SunOS
      • OS X versions prior to 10.3.
      • gcc on any platform prior to version 3.3


    March 15, 2005 - We're pleased to announce the release of OpenEXR 1.2.2. This is a relatively minor update to the project, with the following changes:

    • New build system for Windows; support for DLLs.
    • Switched documentation from HTML to PDF format.
    • IlmImf: support for image layers in ChannelList.
    • IlmImf: added isComplete() method to file classes to check whether a file is complete.
    • IlmImf: exposed staticInitialize() in ImfHeader.h in order to allow thread-safe library initialization in multithreaded applications.
    • IlmImf: New "time code" standard attribute.
    • exrdisplay: support for displaying wrap-around texture map images.
    • exrmaketiled: can now specify wrap mode.
    • IlmImf: New "wrapmodes" standard attribute to indicate extrapolation mode for mipmaps and ripmaps.
    • IlmImf: New "key code" standard attribute to identify motion picture film frames.
    • Imath: Removed TMatrix<T> classes; these classes are still under development and are too difficult to keep in sync with OpenEXR CVS.


    August 10, 2004 - ILM's OpenEXR color management proposal, presented at the Siggraph 2004 "OpenEXR, Film and Color" Birds of a Feather meeting, is now available online. See the documentation section.


    June 6, 2004 - OpenEXR 1.2.1 is now available. This is a fairly minor release, mostly just a few tweaks, a few bug fixes, and some new documentation. Here are the most important changes:

    • reduced memory footprint of exrenvmap and exrmaketiled utilities.
    • IlmImf: new helper functions to determine whether a file is an OpenEXR file, and whether it's scanline- or tile-based.
    • IlmImf: bug fix for PXR24 compression with ySampling != 1.
    • Better support for gcc 3.4.
    • Warning cleanups in Visual C++.


    May 11, 2004 - OpenEXR 1.2.0 is now available. This is the first official, production-ready release since OpenEXR 1.0.7. If you have been using the development 1.1 series, please switch to 1.2.0 as soon as possible. We believe that OpenEXR 1.2.0 is ready for use in shipping applications. We have been using it in production at ILM for several months now with no problems. There are quite a few major new features in the 1.2 series as compared to the original 1.0 series:

    • Support for tiled images, including mipmaps and ripmaps. Note that software based on the 1.0 series cannot read or write tiled images. However, simply by recompiling your software against the 1.2 release, any code that reads scanline images can read tiled images, too.
    • A new Pxr24 compressor, contributed by Pixar Animation Studios. Values produced by the Pxr24 compressor provide the same range as 32-bit floating-point numbers with slightly less precision, and compress quite a bit better. The Pxr24 compressor stores UINT and HALF channels losslessly, and for these data types performs similarly to the ZIP compressor.
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