OpenEXR: The History of a VFX Industry Standard
What is OpenEXR and why you should be using it
You might think file formats are just technical details, but OpenEXR's story reveals how a single innovation can impact an entire industry. When ILM realized they needed better image handling after working on Star Wars: Episode 1, they didn't just solve their own problem—they sparked a revolution in visual effects.
What is OpenEXR?
OpenEXR (or simply EXR) is a high-dynamic range, multi-channel raster file format designed for professional-grade image storage in the motion picture industry. The file format is designated with the .EXR extension and simply put it allows you to store floating point images without the need to compress or convert to a log format, and it can also store additional channels of data such as render passes, masks and metadata.
While many image formats struggle to capture the full range of light and color that exists in nature EXRs are capable of storing a near infinite range of values. OpenEXR has become widely adopted in the computer graphics industry, particularly for visual effects and 3D animation.
Importance in the VFX and 3D industries
You'll find OpenEXR's influence in nearly every major film production since its release in 2003, fundamentally changing how VFX artists work with motion picture imagery.
What makes OpenEXR indispensable in modern VFX workflows? Consider these game-changing capabilities:
- Preserves subtle lighting details that would be lost in traditional formats
- Supports complex compositing with multiple layers and depth information
- Maintains consistent image quality across different software platforms
While other formats struggled with limited color depth and compression artifacts, OpenEXR's floating-point precision opened new creative possibilities.
Comparison with Other File Formats
While traditional image formats like JPEG and PNG, are acceptable for content delivery on websites, apps and other less critical applications, but for VFX, 3D and filmmaking OpenEXR's ability to store floating-point color values gives it a massive advantage in preserving highlight and shadow detail as well as full color information.
Advantages over traditional image formats
Compared to traditional 8-bit image formats like JPEG and PNG, OpenEXR's 16-bit floating-point architecture revolutionized how artists capture and manipulate light in digital imagery.
You can store multiple layers such as depth information and motion vectors in a single file, something impossible with legacy formats.
Comparison with RAW image formats
Unlike RAW image formats that capture sensor data directly from cameras, OpenEXR serves a fundamentally different purpose in the filmmaking pipeline. While RAW formats preserve the original sensor data for post-processing flexibility, OpenEXR excels at storing and manipulating already-processed high dynamic range imagery across multiple stages of the filmmaking process.
RAW formats are often camera-specific and usually proprietary, but OpenEXR's open standard allows universal compatibility across different software and platforms.
Additionally, where RAW files contain a single exposure's worth of data, OpenEXR can store multiple layers, masks, and even 3D information within a single file. This distinction has made OpenEXR indispensable in VFX, as it lets you freely move between applications while preserving complex image data that would be lost in traditional RAW formats.
Origins and Development
It would be easy to assume that the OpenEXR format emerged from a major software company, but it actually sprang from the practical needs of Industrial Light & Magic during their groundbreaking work on Star Wars: Episode 1.
1999 - Creation by Industrial Light & Magic (ILM)
As digital visual effects reached new heights in the late 1990s, Industrial Light & Magic (ILM) faced a critical challenge, they needed a more sophisticated way to handle high-dynamic-range imagery without resorting to degrading and compressing the image. The ILM team, led by Florian Kainz, set out to create a format that would revolutionize how the industry handled image data.
One of the co-creators, Rob Bogart summarized it best:
We would say that images are for two things: they’re for looking at and they’re for making more images. And so image file formats like JPG and PNG are good for looking at things, you look at the picture and then you’re finished. But to make more images, you need a lot of quality in the data, and there wasn’t really a good choice back then – OpenEXR filled that need.
Additionally, Florian Kainz, explained that the creation of OpenEXR was closely tied to the development of a new compositing system that used 16-bit integer and 32-bit floating-point image samples. This approach proved highly effective, necessitating a file format capable of storing these floating-point images without compromising quality.
What was used before EXR?
Prior to the development of OpenEXR, the visual effects industry primarily relied on two file formats for high-quality image storage: DPX (Digital Picture Exchange) and CIN (Cineon).
DPX, standardized by SMPTE, and Cineon, developed by Kodak, were both designed to handle film scans and utilized a logarithmic encoding to preserve the wide dynamic range of film negatives. These formats typically stored 10-bit log-encoded data, which provided a good balance between file size and image quality for the time.
However, the logarithmic encoding meant that more data was stored in the shadows (where our human eyes are more sensitive to changes) and less in the highlights. Then as visual effects techniques advanced, particularly with the increasing use of computer-generated imagery, these limitations became more and more problematic.
Thus the team at ILM set out to solve this issue, and introduced a number of new advancements at the same time.
2001 - Let the Magic Begin
The first major production to fully embrace OpenEXR was "Harry Potter and the Sorcerer's Stone" in 2001. This adoption marked a significant milestone for the format, as it demonstrated its practical benefits in a high-profile visual effects project. The success of OpenEXR in this production helped pave the way for its wider acceptance in the industry.
Since 2001, OpenEXR has been used in all motion pictures with visual effects work by ILM Here are a few of the noteworthy early films to utilize the format.
- "Men in Black II" (2002)
- "Gangs of New York" (2002)
- "Signs" (2002)
2003 - Open to the Public
Following four years of internal development and success, ILM made the groundbreaking decision to release OpenEXR as open-source software in 2003, marking one of the first instances where a major VFX studio shared its proprietary technology with the broader community.
What's particularly striking about this release was its timing - when open source was still viewed with skepticism in enterprise environments. You'd typically find open-source projects driven by enthusiasts, not major studios.
Yet George Lucas himself approved the initiative, recognizing its potential to elevate the entire industry's capabilities. The gamble paid off: Apple quickly incorporated OpenEXR support into macOS, and leading VFX houses embraced the format.
This move didn't just democratize high-end image processing; it demonstrated how sharing technological advances could benefit everyone in the VFX community.
2007 - Academy Award for Technical Achievement
In 2007, OpenEXR received significant recognition from the film industry when it was honored with an Academy Award for Technical Achievement. This award, presented by the Academy of Motion Picture Arts and Sciences, acknowledged the format's substantial impact on visual effects and computer graphics in filmmaking.
The award was specifically given to Florian Kainz for the design and engineering of OpenEXR. Kainz, as one of the key developers at Industrial Light & Magic (ILM), played a crucial role in creating this high dynamic range image file format.
2013 - Open EXR 2.0
Release of OpenEXR 2.0, introducing support for deep image buffers and multiple images in a single file
2019 - Adoption by the Academy Software Foundation (ASWF)
Since becoming open source in 2003, OpenEXR's journey took a pivotal turn in 2019 when the Academy Software Foundation (ASWF) adopted it as one of its flagship projects. This move wasn't just a change in oversight - it marked a new chapter in OpenEXR's evolution as an industry standard.
Under ASWF's stewardship, OpenEXR has experienced transformative growth through:
- Enhanced collaboration between major studios like Disney, Sony, and DreamWorks
- Streamlined development processes with dedicated technical resources
- Improved documentation and support for developers worldwide
- Regular security updates and maintenance from a broader community
While many open-source projects struggle to maintain momentum, OpenEXR's adoption by ASWF actually accelerated its development.
Technical Specifications
OpenEXR's technical prowess stems from its groundbreaking ability to handle 16-bit and 32-bit floating-point data, far surpassing the limitations of traditional 8-bit formats.
This expanded range lets you capture the full range of lighting variations and color information through multiple data channels, while preserving the finest details in both the brightest highlights and darkest shadows.
Thanks to its innovative compression options, you won't sacrifice storage space for quality, as OpenEXR achieves remarkable file size reduction while maintaining the integrity of your high-fidelity images.
High Dynamic Range (HDR) image format
The revolutionary core of OpenEXR lies in its groundbreaking approach to High Dynamic Range imaging, offering an unprecedented 16-bit floating-point format that captures both the faintest shadow details and the brightest highlights in a single frame.
While traditional 8-bit formats forced artists to choose between preserving shadows or highlights, OpenEXR eliminated this compromise.
- Stores infinite brightness values without clipping
- Maintains fine detail in dark areas without quantization
- Preserves color accuracy across extreme exposure ranges
- Enables realistic light behavior in 3D rendering
This technical breakthrough didn't just improve image quality—it fundamentally changed how artists approach lighting and compositing in visual effects.
Support for 16-bit and 32-bit float data
A pivotal innovation in OpenEXR's architecture lies in its dual support for both 16-bit and 32-bit floating-point data, offering VFX artists unprecedented flexibility in choosing their precision requirements.
16-bit half float strikes an ideal balance between file size and quality, making it the go-to choice for most production workflows. When you need extreme precision, the 32-bit float option becomes your ally, especially in challenging scenarios like deep compositing or complex lighting simulations.
What's remarkable is how OpenEXR lets you mix these formats within the same file - you can store some channels in 16-bit and others in 32-bit, adapting to each project's specific needs while optimizing your storage footprint.
Multiple data channels and passes
While traditional image formats limited artists to basic RGBA channels, OpenEXR revolutionized VFX workflows by introducing unlimited arbitrary data channels within a single file. This breakthrough enabled artists to store multiple render passes, metadata, and technical information all within one EXR container.
Here’s some of the typical types of data stored in an EXR files:
- Beauty passes (diffuse, specular, reflection)
- Technical passes (normals, depth, motion vectors)
- Mask passes (object IDs, material IDs, cryptomattes)
- Custom data channels (particle information, lighting data)
What's particularly clever about OpenEXR's approach is that you can selectively load only the channels you need, dramatically improving performance when working with large files in production environments.
Compression options
Since managing massive image files poses significant storage challenges, OpenEXR pioneered several innovative compression methods that balance quality with efficiency.
These options cater to different needs within the VFX and 3D industries, allowing users to optimize their workflow based on specific requirements.
Lossless Compression Methods
- PIZ (PIZO) Compression:
- Wavelet-based algorithm
- Highly effective for CG imagery with smooth color gradients
- Typically achieves 2:1 to 3:1 compression ratios
- ZIP Compression:
- Based on the zlib library
- Good for images with large areas of solid color
- Compression ratios vary depending on image content
- RLE (Run-Length Encoding):
- Simple and fast compression method
- Effective for images with large areas of constant values
- Often used for mask channels or depth maps
Lossy Compression Methods
- B44 Compression:
- Fixed compression ratio of about 2.28:1
- Designed for real-time playback of image sequences
- Minimal visual artifacts, even with multiple compression/decompression cycles
- DWAA and DWAB (JPEG-like wavelets):
- Lossy compression with adjustable quality settings
- DWAA compresses 32 scanlines together, while DWAB compresses 256
- Achieves high compression ratios with minimal visual impact
Choosing the Right Compression
The choice of compression method depends on several factors:
- Image content (e.g., CG renders, live-action plates, mattes)
- Intended use (e.g., final output, intermediate steps, real-time playback)
- Storage constraints and bandwidth limitations
- Processing power available for compression/decompression
By offering this range of compression options, OpenEXR provides flexibility to balance file size, image quality, and performance based on specific project needs and workflow requirements.
Advantages of Open EXR
(even more reasons why you should be using it)
As mentioned above in the technical specifications, OpenEXR files offer a few advantages simply by its technical design:
- High color fidelity and dynamic range
- 16 & 32 bit floating point
- Support for multiple channels and renders passes
- Efficient compression
Those are the advantages you know already, and here are a few other advantages of the OpenEXR architecture:
Deep image compositing
Deep inside OpenEXR's revolutionary capabilities lies its sophisticated deep image compositing system, which fundamentally transformed how visual effects artists handle complex scenes with multiple overlapping transparent elements.
This feature is particularly valuable when working with complex VFX shots that require precise depth management. Instead of flattening all elements into a single layer, deep compositing stores multiple color and depth samples per pixel, enabling unprecedented control over your scenes.
- Each pixel can contain multiple depth samples, allowing for accurate representation of semi-transparent objects.
- Artists can manipulate objects' depth relationships without re-rendering.
- The system handles complex atmospheric effects like fog and smoke with remarkable precision.
- Integration with modern compositing software enables real-time depth adjustments.
This breakthrough has made previously impossible shots achievable, especially in scenes with intricate particle systems or multiple transparent layers.
Extensive metadata representation
Because digital artists need thorough control over their image data, OpenEXR's extensive metadata system stands as one of its most powerful yet underappreciated features.
It can store essential information about camera parameters, color spaces, and production notes directly within the file format, eliminating the need for external tracking systems.
What's particularly clever about OpenEXR's metadata approach is its flexibility - you're not limited to predefined fields.
You can create custom attributes to track anything from lens distortion coefficients to render passes, making it indispensable for complex VFX pipelines.
While other formats might strip away this crucial information during file handling, OpenEXR preserves these details throughout the entire post-production workflow.
This metadata persistence has proven especially beneficial when projects require multiple vendors or extensive iteration cycles.
Mipmap and Ripmap support
While traditional image formats often struggle with efficient scaling and resolution management, OpenEXR's implementation of mipmap and ripmap support revolutionized how visual effects artists handle multi-resolution image processing.
Mipmaps store pre-filtered versions of your image at progressively lower resolutions, cutting rendering time considerably when you're working with texture maps or complex composites.
But OpenEXR didn't stop there. Its ripmap support takes this concept further by allowing independent scaling in both horizontal and vertical directions.
You can quickly access exactly the resolution you need without unnecessary processing overhead.
Cryptomatte support
As visual effects pipelines grew more complex, OpenEXR's integration of Cryptomatte support transformed how artists handle object isolation and masking in compositing workflows.
This feature is particularly valuable when dealing with complex 3D renders, as it automatically generates ID mattes for every object in your scene.
What makes this feature truly revolutionary is its ability to decode complex object relationships on the fly.
You don’t need to manually track object IDs or create individual matte passes, saving countless hours in post-production while ensuring pixel-perfect results.
Open-source nature and industry support
While many proprietary formats guard their code behind closed doors, OpenEXR's open-source nature has sparked unprecedented collaboration across the VFX industry.
Its source code freely available on GitHub, enabling studios worldwide to customize and enhance the format for their specific needs.
This open approach has led to remarkable industry-wide benefits:
- VFX studios can directly contribute improvements, fixing bugs and adding features that benefit everyone.
- Software developers can seamlessly integrate OpenEXR into their tools without licensing fees.
- Technical artists can study the code to understand how high-dynamic-range imaging works.
- Academic institutions can teach students using real-world industry standards.
The format's transparency has fostered trust and accelerated innovation, making OpenEXR the go-to choice for professional VFX work.
It's a prime example of how open-source collaboration can elevate an entire industry's capabilities.
Future Developments
While OpenEXR's core features have proven remarkably durable over two decades, its development team is constantly pushing the boundaries and enhancing its ability to adapt to emerging technologies in the VFX and 3D industries.
Ongoing Improvements and Updates
- Performance Optimization:
- Continued work on improving read and write speeds
- Enhancing multi-threading capabilities for faster processing
- Expanded Color Management:
- Integration with ACES (Academy Color Encoding System) workflows
- Support for wider color gamuts and higher bit depths
- Cloud and Network Optimizations:
- Developing more efficient streaming capabilities for cloud-based workflows
- Improving support for distributed rendering and collaborative environments
- Enhanced Metadata Support:
- Expanding metadata capabilities to include more production-specific information
- Improving interoperability with other file formats and software
Adaptation to Emerging Technologies in VFX and 3D
- Virtual Production Integration:
- Enhancing real-time capabilities for LED wall and virtual set workflows
- Improving compatibility with game engines used in virtual production
- Machine Learning and AI:
- Developing features to support AI-driven compositing and image processing
- Exploring AI-assisted compression techniques for even more efficient storage
- Extended Reality (XR) Support:
- Adapting the format for use in augmented and virtual reality applications
- Enhancing support for light field imagery and volumetric capture
- High Frame Rate and Resolution Support:
- Ensuring compatibility with emerging high frame rate standards (120fps+)
- Optimizing for ultra-high resolution formats (8K and beyond)
- Real-time Ray Tracing:
- Improving support for real-time ray tracing data in game development and visualization
- Sustainability Initiatives:
- Exploring ways to optimize file sizes and processing to reduce energy consumption in render farms and data centers
As the VFX and 3D industries continue to evolve, OpenEXR is likely to remain at the forefront, adapting to new challenges and maintaining its position as a crucial tool in digital content creation. The open-source nature of the format ensures that it will continue to benefit from community contributions and industry-wide collaboration.
Frequently Asked Questions