View source for OpenEXR

{{Short description|Image storage format for the motion picture industry}}
{{Infobox file format
| name          = OpenEXR
| logo          = Openexr logo.svg
| icon          =
| iconcaption   =
| screenshot    =
| caption       =
| extension     = {{mono|.exr}}
| mime          =
| type code     =
| uniform type  = com.ilm.openexr-image<ref>{{cite web |url=https://www.mbsplugins.eu/CGImageSourceSupportedTypes.shtml |title=CGImageSource.SupportedTypes |work=Claris FileMaker MBS Plug-in |publisher=MonkeyBread Software |access-date=2023-05-21 |archive-date=2020-12-30 |archive-url=https://web.archive.org/web/20201230132850/https://mbsplugins.eu/CGImageSourceSupportedTypes.shtml |url-status=live }}</ref>
| conforms to   =
| magic         =
| owner         = [[Industrial Light & Magic]]
| released      = {{Start date and age|1999|df=yes}}
| latest release version = {{wikidata|property|reference|P348}}
| latest release date    = {{start date and age|{{wikidata|qualifier|P348|P577}}}}
| genre         = [[High-dynamic-range imaging]]
| container for =
| contained by  =
| extended from =
| extended to   =
| standard      =
| open          = Yes, [[Modified BSD License]]
| url           = {{Official URL}}
}}
'''OpenEXR''' is a [[high-dynamic-range imaging|high-dynamic range]], multi-channel  [[Raster graphics|raster]] [[file format]], released as an [[open standard]] along with a set of software tools created by [[Industrial Light & Magic]] (ILM), under a [[free software license]] similar to the [[BSD license]].<ref>{{cite web |url=http://www.openexr.com/license.html |title=License |website=openexr.com |access-date=2012-10-28 |archive-date=2012-07-22 |archive-url=https://web.archive.org/web/20120722004110/http://www.openexr.com/license.html |url-status=dead }}</ref>

It is notable for supporting multiple [[Channel (digital image)|channels]] of potentially different pixel sizes, including 32-bit unsigned integer, 32-bit and 16-bit floating point values, as well as various compression techniques which include [[Lossless data compression|lossless]] and [[Lossy data compression|lossy compression]] algorithms. It also has arbitrary channels and encodes multiple points of view such as left- and right-camera images.<ref name="technical_introduction">{{cite web |url=https://people.computing.clemson.edu/~dhouse/courses/404/papers/EXRTechnicalIntroduction.pdf
  |title=Technical Introduction to OpenEXR
  |first1=Florian |last1=Kainz |first2=Rod |last2=Bogart |first3=Piotr |last3=Stanczyk |first4=Peter |last4=Hillman
  |date=5 November 2013
  |publisher=[[Industrial Light & Magic]]
  |access-date=2025-01-05 }}</ref>

==Overview==
A full technical introduction of the format is available on the OpenEXR website.<ref>{{cite web
  |url=https://openexr.com/en/latest/
  |title=OpenEXR
  |author=<!-- not stated -->
  |publisher=LF Projects, LLC
  |access-date=2025-01-05
  |archive-date=2025-01-01
  |archive-url=https://web.archive.org/web/20250101152212/https://openexr.com/en/latest/
  |url-status=live
  }}</ref>

OpenEXR, or EXR for short, is a deep raster format developed by ILM and broadly used in the computer-graphics industry, both visual effects and animation.

OpenEXR's multi-resolution and arbitrary channel format makes it appealing for [[Digital compositing|compositing]], as it alleviates several painful elements of the process. Since it can store arbitrary channels—[[Specularity|specular]], diffuse, [[Alpha compositing|alpha]], RGB, normals, and various other types—in one file, it takes away the need to store this information in separate files. The multi-channel concept also reduces the necessity to "bake" in the aforementioned data to the final image. If a compositor is not happy with the current level of [[specularity]], they can adjust that specific channel.<ref name="EXR_file_layout">{{cite web|url=https://openexr.com/en/latest/OpenEXRFileLayout.html|title=OpenEXR File Layout|access-date=25 May 2023|archive-date=25 May 2023|archive-url=https://web.archive.org/web/20230525173510/https://openexr.com/en/latest/OpenEXRFileLayout.html|url-status=live}}</ref>

OpenEXR's [[Application programming interface|API]] makes tools development a relative ease for developers. Since there are almost never two identical production pipelines, custom tools always need to be developed to address problems (e.g. image-manipulation issue). OpenEXR's library allows quick and easy access to the image's attributes such as tiles and channels.<ref name=EXR_file_layout />

The OpenEXR library is developed in [[C++]] and is available in source format as well as compiled format for [[Microsoft Windows]], [[macOS]] and [[Linux]]. Python bindings for the library are also available for version 2.x.<ref>{{cite web|url=https://pypi.python.org/pypi/OpenEXR|title=OpenEXR 1.3.0 : Python Package Index|website=pypi.python.org|access-date=11 April 2018|archive-date=12 April 2018|archive-url=https://web.archive.org/web/20180412001355/https://pypi.python.org/pypi/OpenEXR|url-status=live}}</ref>

===History===
OpenEXR was created by ILM in 1999 and released to the public in 2003 along with an [[Open-source license|open source]] [[software library]].<ref>{{cite press release |url=http://www.openexr.com/OpenEXR_Press_Release_1_22_03.pdf |date=22 January 2003 |title=Industrial Light & Magic Releases Proprietary Extended Dynamic Range Image File Format OpenEXR to Open Source Community |access-date=11 April 2013 |archive-url=https://web.archive.org/web/20170721234341/http://www.openexr.com/OpenEXR_Press_Release_1_22_03.pdf |archive-date=21 July 2017 |url-status=dead }}</ref><ref name="OpenEXRdotCom">{{Cite web|url=https://github.com/AcademySoftwareFoundation/openexr|title=OpenEXR|date=January 16, 2023|via=GitHub}}</ref> It soon received wide adoption by software used in [[computer graphics]], particularly for [[Film production|film]] and [[Television production|television]] production. The format has been updated several times, adding support for tiles, [[mipmaps]], new compression methods, and other features.<ref name=OpenEXRdotCom/> In 2007, OpenEXR was honored with an [[Academy Award for Technical Achievement]].<ref name=OpenEXRdotCom/>

OpenEXR 2.0 was released in April 2013, extending the format with support for [[Deep image compositing|deep image buffers]] and multiple images embedded in a single file.<ref name=OpenEXRdotCom/><ref>{{cite mailing list |url=https://lists.nongnu.org/archive/html/openexr-announce/2013-04/msg00000.html |first=Piotr |last=Stanczyk |title=v2.0.0.0 (GM) release announcement |mailing-list=openexr-announce |date=9 April 2013 |access-date=11 April 2013 |archive-date=19 August 2014 |archive-url=https://web.archive.org/web/20140819102945/https://lists.nongnu.org/archive/html/openexr-announce/2013-04/msg00000.html |url-status=live }}</ref><ref>{{cite news |url=http://www.cgsociety.org/index.php/CGSFeatures/CGSFeatureSpecial/openexr_2.0 |title=OpenEXR 2.0 |date=10 April 2013 |work=The CGSoceity |archive-date=14 April 2013 |access-date=11 April 2013 |archive-url=https://web.archive.org/web/20130414015235/http://www.cgsociety.org/index.php/CGSFeatures/CGSFeatureSpecial/openexr_2.0 |url-status=live }}</ref> Version 2.2, released August 2014, added the lossy DWA compression format.<ref name="OpenEXR 2.2">{{cite press release|date=8 August 2014|title=DreamWorks Animation Contributes Lossy Compression To OpenEXR 2.2|url=https://www.renderosity.com/dreamworks-animation-contributes-lossy-compression-to-openexr-2-2-cms-17221|location=Glendale, CA|access-date=2014-08-18|archive-date=2014-08-19|archive-url=https://web.archive.org/web/20140819083921/http://www.renderosity.com/dreamworks-animation-contributes-lossy-compression-to-openexr-2-2-cms-17221|url-status=live}}</ref>

==Distribution==
The OpenEXR software distribution includes:
* libraries
* Half, a C++ class for manipulating half values as if they were a built-in C++ data type
* exrdisplay, a sample application for viewing OpenEXR images on a display at various exposure settings

===Libraries===
* {{mono|IlmImf}}<ref>{{Cite web|url=https://www.openexr.com/documentation/ReadingAndWritingImageFiles.pdf|title=Reading and Writing OpenEXR Image Files with the IlmImf Library}}</ref> = library made by [[Industrial Light & Magic]] (Ilm) for  low-level operations on the files with OpenEXR  image format (Imf)<ref>{{Cite web|url=https://github.com/AcademySoftwareFoundation/openexr/issues/879|title=name · Issue #879 · AcademySoftwareFoundation/openexr|website=GitHub}}</ref>
** {{mono|libIlmImf}} on linux
** {{mono|IlmImf.dll}} on windows
* {{mono|IlmImfUtil}}
* {{mono|Imath}}<ref>{{Cite web|url=https://github.com/AcademySoftwareFoundation/Imath|title=Imath|date=January 21, 2023|via=GitHub|access-date=December 21, 2020|archive-date=December 22, 2020|archive-url=https://web.archive.org/web/20201222162945/https://github.com/AcademySoftwareFoundation/Imath|url-status=live}}</ref>

==Color depth==
OpenEXR has support for [[color depth]] using:
* 16-bit floating-point (half)
* 32-bit floating-point
* 32-bit unsigned integer

==Compression methods==
There are three general types of lossless compression built into OpenEXR, with two different methods of Zip compressing. For most images without a lot of grain, the two Zip compression methods seem to work best, while the PIZ compression algorithm is better suited to grainy images. The following options are available:<ref>{{Cite web |url=http://www.openexr.com/TechnicalIntroduction.pdf#%5B%7B%22num%22%3A47%2C%22gen%22%3A0%7D%2C%7B%22name%22%3A%22XYZ%22%7D%2C69%2C437%2C0%5D |title=Technical Introduction to OpenEXR |access-date=2006-02-23 |archive-url=https://web.archive.org/web/20110717152538/http://www.openexr.com/TechnicalIntroduction.pdf#%5B%7B%22num%22%3A47%2C%22gen%22%3A0%7D%2C%7B%22name%22%3A%22XYZ%22%7D%2C69%2C437%2C0%5D |archive-date=2011-07-17 }}</ref>

; None: Disables all compression.
; [[Run-length encoding|Run Length Encoding (RLE)]]: This is a basic form of compression that is comparable to that used by standard [[Truevision TGA|Targa]] files.
; Zip (per scanline): [[deflate]] compression with [[zlib#Encapsulation|zlib wrapper]] applied to individual [[scanline]]s (not based on the [[ZIP file format]] despite its name).
; Zip (16 scanline blocks): deflate compression applied to blocks of 16 scanlines at time. This tends to be the most effective style of compression to use with rendered images that do not have film grain applied.
; PIZ ([[wavelet]] compression): This lossless method uses a new combined wavelet / [[Huffman coding|Huffman]] compression. This form of compression is quite effective when dealing with grainy images, and will often surpass any of the other options under grainy conditions.
; PXR24 (24-bit data conversion then deflate compression): This form of compression from [[Pixar Animation Studios]] converts 32-bit floats to 24 bits then uses deflate compression. It is lossless for half and 32-bit integer data and slightly lossy for 32-bit float data.
; B44: This form of compression is lossy for half data and stores 32-bit data uncompressed. It maintains a fixed compression size of either 2.28:1 or 4.57:1 and is designed for realtime playback. B44 compresses uniformly regardless of image content. <ref>{{Cite web |url=http://www.openexr.com/TechnicalIntroduction.pdf |title=Technical Introduction to OpenEXR |access-date=2006-02-23 |archive-url=https://web.archive.org/web/20110717152538/http://www.openexr.com/TechnicalIntroduction.pdf |archive-date=2011-07-17 |url-status=dead }}</ref>
; B44A: An extension to B44 where areas of flat color are further compressed, such as alpha channels.
; DWAA: JPEG-like lossy compression format contributed by [[DreamWorks Animation]]. Compresses 32 scanlines together.<ref name="OpenEXR 2.2"/>
; DWAB: Same as DWAA, but compresses blocks of 256 scanlines.

==Credits==
From OpenEXR.org's Technical Introduction:

<blockquote>The ILM OpenEXR file format was designed and implemented by Florian Kainz, Wojciech Jarosz, and Rod Bogart. The PIZ compression scheme is based on an algorithm by Christian Rouet. Josh Pines helped extend the PIZ algorithm for 16-bit and found optimizations for the float-to-half conversions. Drew Hess packaged and adapted ILM's internal source code for public release and maintains the OpenEXR software distribution. The PXR24 compression method is based on an algorithm written by Loren Carpenter at Pixar Animation Studios.<ref name="technical_introduction"/> </blockquote>

==See also==
* [[High dynamic range]]

==References==
{{Reflist}}

==External links==
* {{Official website}}
* [http://scanline.ca/exrtools/ exrtools incl. exrtoppm exe]

{{Graphics file formats}}

[[Category:Free graphics software]]
[[Category:High dynamic range]]
[[Category:High dynamic range file formats]]
[[Category:Lucasfilm]]
[[Category:Open formats]]
[[Category:Raster graphics file formats]]
[[Category:Software using the BSD license]]