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Reference Formats

MOS

MOS is the raw format used by Leaf's medium-format digital camera backs, a TIFF/EXIF-derived structure that continued in use after Phase One acquired Leaf in 2009.

Extension

.mos

Full name

Leaf Camera RAW

Introduced

circa 2002, with Leaf's Valeo line of digital backs; continued after Phase One's 2009 acquisition of Leaf

Vendor

Phase One (originally Leaf Systems, acquired 2009)

What is inside the container

MOS uses a TIFF/EXIF file structure as its base but is not fully TIFF-compliant, storing raw sensor data as uncompressed or JPEG-lossless-compressed grayscale (single-plane, pre-demosaic) images. It was used across Leaf's Valeo, Cantare, and Volare digital backs and continued into the Aptus series. Leaf became a Phase One-owned brand in 2009, and later Leaf/Mamiya Leaf backs eventually shifted to Phase One's own IIQ format, making MOS effectively a legacy format tied to discontinued hardware.

How to open it

Windows / macOS Capture One, which supports MOS as part of Phase One's unified raw processing after the Leaf acquisition
Windows / macOS Adobe Camera Raw / Lightroom Classic, for uncompressed MOS files (compressed MOS from some Leaf backs is not supported by Camera Raw)
Cross-platform, open source darktable, via RawSpeed with support for Leaf/Mamiya Leaf backs
Legacy Leaf native Leaf Capture / Leaf Raw Converter, Leaf's original discontinued software

For archives

MOS is tied to discontinued Leaf digital-back hardware from a brand that no longer exists independently, and Leaf's own conversion software is unmaintained, making this one of the more archivally fragile formats in this list. Convert MOS assets to DNG for any DAM holding legacy medium-format archives, and do so proactively rather than waiting for compatibility gaps to appear in current software.

MOS traces back to Leaf, a Massachusetts-based company that shipped one of the earliest medium-format digital camera backs, the Leaf DCB1, in 1991. The MOS extension itself became associated with Leaf’s raw output through the Valeo family of portable digital backs launched from 2002 onward, and continued through later Leaf lines including Cantare, Volare, and Aptus. Leaf built its business specifically around high-resolution backs for Hasselblad, Mamiya, and Contax medium-format camera bodies.

Structurally, MOS uses a TIFF/EXIF base but does not fully comply with the TIFF standard, and it stores raw data as a single grayscale sensor plane — uncompressed or with JPEG lossless compression — reflecting the pre-demosaic Bayer data straight off the back’s CCD sensor. Phase One acquired Leaf from Kodak in 2009, and the Leaf and Mamiya brands were later consolidated under Phase One, with subsequent Leaf-branded backs eventually adopting Phase One’s own IIQ format instead of MOS.

That corporate history matters directly for archival planning: MOS is now a format tied to hardware nobody manufactures anymore, from a brand absorbed into a larger company years ago. Leaf’s own raw converter software is effectively frozen in time, and while Capture One and Adobe Camera Raw still handle most MOS files, compressed variants from certain Leaf backs are already outside Camera Raw’s support. A DAM holding legacy medium-format archives with MOS files should treat DNG conversion as a near-term priority rather than an eventual nice-to-have.

Frequently asked

Why is MOS considered one of the more archivally fragile formats for a DAM?

MOS is tied to discontinued Leaf digital-back hardware from a brand that no longer exists independently, and Leaf's own conversion software is unmaintained, making it one of the more fragile formats in this list.

What happened to the Leaf brand behind MOS?

Leaf Systems was founded in Massachusetts in 1984, acquired by Israel's Scitex in 1992, passed to Creo in 2000, then to Eastman Kodak in 2005. In June 2009 Phase One, together with Leaf's own management, bought the Leaf assets from Kodak and formed Leaf Imaging Ltd. Phase One later folded Leaf engineering into its Credo back line, which writes the newer IIQ raw format, leaving MOS a closed, legacy-only format tied to discontinued hardware.

Is MOS fully TIFF-compliant?

No. MOS reuses the TIFF/EXIF container structure — IFD tags, byte order, EXIF metadata block — so generic TIFF readers can open the file and read basic header data, but the image data itself breaks TIFF conventions: it stores single-plane, pre-demosaic grayscale sensor data, either uncompressed or JPEG-lossless-compressed, rather than standard RGB or CMYK pixel planes. That mismatch is why plain TIFF viewers show a valid header but cannot render a correct color image.

Does Adobe Camera Raw support all MOS files?

No. Camera Raw reads uncompressed MOS files reliably but has patchy support for the JPEG-lossless-compressed variant that later Leaf backs, including higher-resolution Aptus models, wrote by default to save storage. Depending on the Camera Raw or DNG Converter version installed, compressed MOS files can fail to open, decode with artifacts, or require an older release to work at all. This version-dependent gap is a known compatibility trap for archives holding mixed-generation Leaf captures.

What should a DAM do with MOS assets in a legacy medium-format archive?

Treat MOS like other orphaned raw formats: keep the original .mos file untouched as the archival master, but generate and store a DNG or TIFF derivative at ingest so the asset stays viewable as native decoder support keeps eroding. Record capture metadata — Leaf back model and compression mode — in the DAM's own fields before it is lost, since EXIF alone won't reliably distinguish compressed from uncompressed variants. Re-test renders periodically against current software, since Adobe support is uneven.

What Leaf digital-back product lines used MOS?

MOS was Leaf's native raw format across its digital-back generations for medium-format camera bodies: the early Valeo series, the Cantare and Volare backs, and the later, higher-resolution Aptus and Aptus-II line mounted on Mamiya, Hasselblad, and other medium-format systems. All of them wrote MOS regardless of resolution or release year; Phase One only switched newer backs to the IIQ format after absorbing Leaf's engineering in 2009.

What current software still supports MOS?

Capture One, Phase One's own raw processor, offers the most complete current support since Phase One now owns the Leaf legacy. Adobe Camera Raw and Lightroom still open uncompressed MOS files but are inconsistent with compressed ones depending on version. Darktable, the open-source raw editor, decodes MOS through its bundled RawSpeed library, giving archives a maintained, license-free fallback path that doesn't depend on Adobe's or Phase One's release cycles.

When was MOS introduced?

Leaf introduced the MOS format around 2002 alongside its Valeo digital-back series, one generation before the Cantare, Volare, and Aptus lines that followed it. That predates Phase One's ownership of Leaf by roughly seven years, meaning every MOS file in circulation was captured on hardware that is now well over two decades old — a factor worth weighing when prioritizing which legacy assets to migrate first.

Sources