OpenEXR Technical Documentation

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.

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.

Technical Documents

• Technical Introduction to OpenEXR
• Reading and Writing OpenEXR Image Files with the OpenEXR Library
• Reading and Writing OpenEXR Image Files with the C-language API
• OpenEXR File Layout
• Storing Multi-View Images in OpenEXR Files
• Interpreting OpenEXR Deep Pixels
• Theory of Deep Samples
• Standard Optional Attributes

• Index

Resources

• Download: https://github.com/AcademySoftwareFoundation/openexr

• Install Help: INSTALL.md

• Porting Help: Imath/OpenEXR Version 2->3 Porting Guide

• License: BSD License

• Reference images: https://github.com/AcademySoftwareFoundation/openexr-images

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.