Why convert MOS to HEIC instead of JPG for previews?

Medium-format work is bought for tonal smoothness, and 8-bit JPG previews can band on exactly the gradients clients scrutinize - backdrops, sky, automotive paint. HEIC's 10-bit pipeline avoids that at half the file size, and renders natively on the iPads and iPhones where most client review happens. JPG remains the right choice for Windows-heavy review chains and web proofing platforms.

More about converting MOS to HEIC

MOS is the RAW format used by Mamiya Leaf medium-format digital backs - the Aptus, Aptus-II, Credo, and the Mamiya Leaf Credo line that mounted on Mamiya 645DF, Phase One XF, and Hasselblad H bodies. Resolutions run from 22MP (Aptus 22) up to 80MP (Credo 80). Commercial product photographers, automotive shooters, and luxury real-estate teams convert MOS to HEIC for client preview galleries: an 80MP frame that weighs 25MB as a quality JPG lands around 12-15MB as HEIC at the same visual quality, halving gallery load times and iPad storage on set.

Capture One Pro is the de facto MOS processor because Phase One acquired Leaf in 2014 and integrated per-back profiles deeply. The sensible pipeline is to develop in Capture One with lens cast correction applied, export a 16-bit TIFF for the retoucher, and generate HEIC previews for client review. HEIC's 10-bit color support is a genuine advantage at this end of the market: medium-format files are prized for tonal smoothness, and 8-bit JPG previews visibly band on studio backdrops and automotive paint gradients where 10-bit HEIC holds clean.

Client-side, HEIC previews shine in Apple-centric review workflows - art directors approving on iPads, gallery links opened on iPhones - where the format renders natively at half the bandwidth. The limits: PowerPoint on Windows, most web-based proofing platforms, and print bureaus expect JPG or TIFF, and Windows reviewers need the HEVC codec installed. Convert MOS to HEIC for the Apple review loop and keep HEIC to JPG handy for the deliverables that must travel further.

When you'd use this

Reasons to convert MOS to HEIC usually come down to compatibility, file-size, or specific feature requirements. Common situations:

An app or platform only accepts HEIC uploads.
You need a feature unique to HEIC (e.g. transparency, vector scaling, animation, multi-page pages, etc.) that MOS doesn't provide.
You're optimising file size — modern formats often produce smaller files than the older format you started with.
You need a single archival format across a project so files behave consistently in the same viewer.

How to do it in heic.now

Open the MOS → HEIC tool on heic.now.
Drag your MOS file onto the drop zone, or click Select files. You can drop a whole folder of files at once.
The output is fixed to HEIC. If the format supports extra options (page size, transparency background, quality, EXIF stripping), tweak them in the right-hand panel.
Click Convert. The job runs on our server and finishes in a few seconds for typical photos.
Download the result. Files stay in storage for 24 hours and are then permanently deleted.

The entire flow is free for the first 10 jobs per day with no signup required. A free account doubles that quota; a premium plan removes the limit entirely.

Tips and common pitfalls

Develop in Capture One Pro with lens cast correction (LCC) applied before converting - the HEIC bakes in whatever the export contains, magenta cast included.
Use HEIC for iPad/iPhone client review loops - 10-bit color keeps backdrop and paint gradients smooth where 8-bit JPG previews band.
Export 16-bit TIFF for retouchers and print - HEIC is a preview and delivery format, not a retouching intermediate.
Strip back serial number and shoot date from EXIF before client delivery - HEIC preserves full metadata through conversion unless you remove it.
For 80MP+ backs, resize to 8192px long edge on export before HEIC conversion - full-resolution previews waste bandwidth on any screen a client will actually use.