What Is .ora

Overview

.ORA (Open Raster) is an open-source file format designed for storing layered raster images, created as a universal alternative to proprietary formats like Adobe's PSD. The format was officially proposed in 2006 at the first Libre Graphics Meeting in Lyon, France, by KDE and Krita developers Boudewijn Rempt and Cyrille Berger, drawing inspiration from the Open Document Format architecture. It represents a collaborative effort in the open-source graphics community to establish a standardized, transparent format for digital art that maintains full compatibility across multiple applications.

The technical foundation of ORA lies in its ZIP container structure, which contains all image components including layers, metadata, color profiles, and embedded resources. Unlike proprietary formats that keep their specifications closed, ORA's open specification allows any developer to implement support, fostering broader adoption across digital art applications. Today, the format is supported by numerous graphics editors including GIMP, Krita, MyPaint, XnView, and Paint.NET, making it an increasingly viable option for professional and amateur digital artists alike.

How It Works

OpenRaster files function as ZIP archives containing a structured directory tree with multiple components working together to preserve all aspects of a digital artwork.

• ZIP Container Architecture: ORA files are fundamentally ZIP files using DEFLATE or STORED compression methods. This architecture makes the format transportable, compressible, and inspectable—users can extract and examine the file contents using any standard ZIP utility without specialized software.
• Layer System: The format stores individual layers as PNG images within the archive, each with its own properties including opacity, blend mode, and visibility settings. This allows complete preservation of an artist's layering structure when exchanging files between different graphics applications.
• Metadata and XML: A stack.xml file within the ORA archive contains all layer information, document dimensions, color spaces, and other metadata in human-readable XML format. This transparent structure enables developers to extend functionality while maintaining backward compatibility with the base specification.
• Required Image Files: Every valid ORA file must contain a thumbnail.png (non-interlaced, 8-bit, maximum 256x256 pixels) for efficient file browser rendering and a mergedimage.png showing the flattened composite. These files ensure that ORA images display properly in file managers and viewer software that don't fully support the format.
• Color Management: The format supports embedded color profiles and preserves color information across applications, maintaining color accuracy when files are opened in different graphics editors. This is critical for professional digital artists who require consistent color representation across workflows.

Key Comparisons

Why It Matters

The ORA format addresses a critical need in the digital art community for an open, vendor-neutral interchange format that doesn't lock users into proprietary software ecosystems.

• Accessibility and Transparency: Because ORA is based on the open ZIP standard with publicly documented specifications, any developer can create tools to read, write, and extend the format. This democratization stands in stark contrast to proprietary formats that require reverse-engineering or licensing agreements.
• Professional Workflow Integration: Digital artists working with multiple applications can now save their projects in ORA format without sacrificing layers, transparency, or metadata when switching between GIMP, Krita, MyPaint, and other tools. This eliminates the need to maintain separate project files in different formats.
• Preservation and Archiving: The transparent, XML-based metadata structure of ORA files ensures that digital artworks can be preserved long-term. Unlike proprietary formats that may become obsolete, ORA's open specification guarantees that future tools can always read and extract the data.
• Community-Driven Development: The OpenRaster specification (currently at version 0.0.6) is maintained collaboratively by the open-source graphics community rather than a single corporation. This ensures that the format evolves to meet genuine user needs and incorporates innovations from multiple perspectives.

As digital art continues to grow as both a professional field and creative hobby, standardized, open formats like ORA become increasingly important. The format provides artists with freedom to choose their tools without worrying about proprietary lock-in, while simultaneously supporting interoperability across the diverse landscape of graphics applications. For anyone serious about open-source digital creation, ORA represents both a practical tool and a philosophical commitment to transparent, collaborative standards in creative software.