What is the ORF file format?
A .orf file is an Olympus Raw Format image data file created by an Olympus or OM System digital camera. The .orf file contains an unprocessed RAW photo, information about it, and headers that hold data on saturation, color temperature, and contrast. Headers also contain metadata, including data related to the camera with which the photo was taken. The format is built on a TIFF/EP-based binary container with an Olympus-specific magic signature - most files begin with the bytes IIRO or IIRS at offset 0.
Images captured by the camera's sensor are saved into the .orf file without any in-camera processing. .orf files recreate the original image as close as possible with a realistic color palette, and are therefore more open to advanced editing than JPEG images. The format allows users to adjust parameters such as saturation, contrast, and white balance without quality loss. Viewing .orf files requires dedicated raw-processing software such as OM Workspace, Adobe Lightroom, RawTherapee, or darktable.
JPEG images contain only 8 bits per pixel per channel, while .orf images have 12 or 14 bits per pixel per channel. .orf images therefore store more information, resulting in higher image quality, greater editing headroom, and larger file sizes. For archiving or cross-platform workflows, .orf files can be converted to the open DNG format.
Security & safety
RISK: LOWORF is a passive image data file - sensor data and metadata, not executable code - so opening one is safe. The practical cautions are non-malware: ORF is large and proprietary, so back up originals and consider archiving to open DNG for longevity; and EXIF/MakerNote metadata (camera, often GPS, timestamps) travels with the file - strip it before publishing if privacy matters. Editing is non-destructive in raw developers, so the original ORF is preserved. Beware dubious "ORF viewer/converter" downloads from ad portals; use the tools listed here.
Format details
in a nutshellPrograms that open ORF files
Windows6 apps
darktable
Open-source Free Lightroom-style raw developer; import the ORF to edit non-destructively and export JPG/TIFF. 
RawTherapee
Open-source Free, powerful raw processor with good Olympus demosaicing; open the ORF and export. 
Raw Image Extension (Microsoft Store)
Free Install from the Microsoft Store to show ORF thumbnails/previews in File Explorer and the Photos app.
OM Workspace
Free OM System's own free raw editor (successor to Olympus Viewer 3); opens and develops ORF natively with model-accurate colour.
Adobe Lightroom / Photoshop (Camera Raw)
Paid Import the ORF; Camera Raw develops it. Industry standard but subscription-based. 
XnView MP
Free Views ORF (via embedded preview / raw decode) and batch-converts to JPG with XnConvert. 
macOS3 apps
Apple Photos / Preview
Built-in macOS has built-in Olympus raw support; double-click to preview, or import into Photos to view/edit ORF. 
Linux3 apps
GIMP (+ darktable/RawTherapee plugin)
Open-source GIMP opens ORF via its darktable/RawTherapee raw loader, then edits as a normal image. Technical details
deep spec| Container format | TIFF/EP-based binary container with Olympus-specific proprietary IFD extensions |
| File signature | IIRO (49 49 52 4F) or IIRS (49 49 52 53) at byte offset 0 - an Olympus variant of the TIFF little-endian header |
| Byte order | Little-endian (Intel), indicated by the II prefix inherited from the TIFF specification |
| Bit depth | 12 or 14 bits per pixel per channel, depending on the camera model and sensor generation |
| MIME type | image/x-olympus-orf |
| Raw data encoding | Uncompressed or lossless-packed Bayer sensor data; no in-camera lossy processing is applied |
| Color filter array | Bayer RGGB mosaic; demosaicing is deferred entirely to post-processing software |
| Embedded metadata | EXIF IFD plus Olympus/OM System proprietary MakerNote tags covering AF data, scene recognition, and lens identity |
| Embedded preview | Reduced-size or full-resolution JPEG thumbnail stored inside the file for fast browsing without full decode |
| White balance storage | WB setting recorded as metadata only; raw sensor data is not altered by the in-camera white balance selection |
| Lens correction data | Distortion, chromatic aberration, and vignetting correction coefficients stored in the Olympus MakerNote IFD |
| Proprietary status | Specification is unpublished; support in LibRaw, dcraw, and Adobe Camera Raw achieved through reverse engineering |
| Released | circa 2002 (early Olympus E-system / C-series cameras); still used on current OM System bodies |
| Specification | www.om-digitalsolutions.com |
ORF conversions
Community Q&A
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