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OpenEXR

OpenEXR provides the specification and reference implementation of the EXR file format, the professional-grade image storage format of the motion picture industry.

The purpose of EXR format is to accurately and efficiently represent high-dynamic-range scene-linear image data and associated metadata, with strong support for multi-part, multi-channel use cases.

OpenEXR is widely used in host application software where accuracy is critical, such as photorealistic rendering, texture access, image compositing, deep compositing, and DI.

About OpenEXR

OpenEXR is a project of the Academy Software Foundation. The format and library were originally developed by Industrial Light & Magic and first released in 2003. Weta Digital, Walt Disney Animation Studios, Sony Pictures Imageworks, Pixar Animation Studios, DreamWorks, and other studios, companies, and individuals have made contributions to the code base.

OpenEXR is included in the VFX Reference Platform.

OpenEXR Features

  • High dynamic range and color precision.
  • Support for 16-bit floating-point, 32-bit floating-point, and 32-bit integer pixels.
  • 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 stereoscopic image workflows and a generalization to multi-views.
  • 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 accommodated.
  • 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.

OpenEXR and Imath Version 3

With the release of OpenEXR 3, the Imath library formerly distributed via the IlmBase component of OpenEXR is now an independent library dependency, available for download from https:://github.com/AcademySoftwareFoundation/Imath. You can choose to build OpenEXR against an external installation of Imath, or the default CMake configuration will download and build it automatically during the OpenEXR build process. Note that the half 16-bit floating point data type is included in Imath.

See the 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.

New Features in OpenEXR v3.1

The 3.1 release of OpenEXR introduces a new library, OpenEXRCore, which is the result of a significant re-thinking of how OpenEXR manages file I/O and provides access to image data. It begins to address long-standing scalability issues with multithreaded image reading and writing.

The OpenEXRCore library provides thread-safe, non-blocking access to files, which was not possible with the current API, where the framebuffer management is separate from read requests. It is written entirely in C and provides a new C-language API alongside the existing C++ API. This new low-level API allows applications to do custom unpacking of EXR data, such as on the GPU, while still benefiting from efficient I/O, file validation, and other semantics. It provides efficient direct access to EXR files in texturing applications. This C library also introduces an easier path to implementing OpenEXR bindings in other languages, such as Rust.

The 3.1 release represents a technology preview for upcoming releases. The initial release is incremental; the existing API and underlying behavior has not changed. The new API is available now for performance validation testing, and then in future OpenEXR releases, the C++ API will migrate to use the new core in stages. It is not the intention to entirely deprecate the C++ API, nor must all applications re-implement EXR I/O in terms of the C library. The C API does not, and will not, provide the rich set of utility classes that exist in the C++ layer. The 3.1 release of the OpenEXRCore library simply offers new functionality for specialty applications seeking the highest possible performance. In the future, the ABI will evolve, but the API will remain consistent, or only have additions.

See Reading and Writing OpenEXR Image Files with the C-language API for more information.

Supported Platforms

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

OpenEXR Project Mission

The goal of the OpenEXR project is to keep the EXR format reliable and modern and to maintain its place as the preferred image format for entertainment content creation.

Major revisions are infrequent, and new features will be carefully weighed against increased complexity. The principal priorities of the project are:

  • Robustness, reliability, security
  • Backwards compatibility, data longevity
  • Performance - read/write/compression/decompression time
  • Simplicity, ease of use, maintainability
  • Wide adoption, multi-platform support - Linux, Windows, macOS, and others

OpenEXR is intended solely for 2D data. It is not appropriate for storage of volumetric data, cached or lit 3D scenes, or more complex 3D data such as light fields.

The goals of the IlmBase project are simplicity, ease of use, correctness and verifiability, and breadth of adoption. IlmBase is not intended to be a comprehensive linear algebra or numerical analysis package.

OpenEXR Project Governance

OpenEXR is hosted by the Academy Software Foundation. See GOVERNANCE for more information about how the project operates.

The OpenEXR project is dedicated to promoting a harassment-free community. Read our code of conduct.

Developer Quick Start

See INSTALL for instructions on downloading and building OpenEXR from source.

Resources

Getting Help

There are several ways to connect with the OpenEXR project:

  • The openexr-dev@lists.aswf.io mail list: This is a development focused mail list with a deep history of technical conversations and decisions that have shaped the project. Subscribe at openexr-dev@lists.aswf.io.

  • ASWF Slack channel: #openexr

  • GitHub Issues: GitHub issues are used both to track bugs and to discuss feature requests.

See CONTRIBUTING for more information.

Getting Involved

OpenEXR welcomes contributions to the project. See CONTRIBUTING for more information about contributing to OpenEXR.

License

OpenEXR is released under the BSD-3-Clause license. See PATENTS for license information about portions of OpenEXR that are provided under a different license.

Frequently Asked Questions

  • "pip install openexr doesn't work."

    The OpenEXR project provides python bindings for the Imath vector/matrix classes, but it does not provide python bindings for reading, writing, or editing .exr files. The openexrpython module is not affiliated with the OpenEXR project or the ASWF. Please direct questions there.

    Alternatively, OpenImageIO also includes python bindings for OpenEXR.


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The OpenEXR project provides the specification and reference implementation of the EXR file format, the professional-grade image storage format of the motion picture industry.

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