Ossidex
Ossidex vs Horos: Free macOS Viewer vs Native iOS App
Updated July 12, 2026 · 6 min read
Horos deserves more credit than it usually gets. It took the OsiriX open-source lineage and kept a serious, free DICOM workstation available to anyone with a Mac — students, residents, small practices, researchers. For a zero-budget desktop setup, Horos is still one of the first things worth installing, and this page will not pretend otherwise.
The honest caveats are also well known: Horos runs only on macOS, there is no iOS version at all, and development has slowed to the point where major macOS updates are an annual source of anxiety for its users. Ossidex is not a fork of anything — it is a native iOS viewer written for Metal-era hardware — so this comparison is less "which is better" and more "which problem do you actually have."
Side-by-Side
| Ossidex | Horos | |
|---|---|---|
| Platform | iPad + iPhone, native iOS app | macOS only — no iOS version |
| Price | Free download; optional Pro plans in App Store | Open source; check current project terms |
| Maintenance | Actively developed | Development has slowed; infrequent releases |
| Offline use | 100% on-device, no account | Yes (desktop, local database) |
| Dental tools | Arch/panoramic CPR + cross-sections, tooth numbering, Misch HU probe, CBCT presets | None dental-specific; generic CT tools |
| PACS | DICOMweb (QIDO/WADO), Basic + OAuth2 PKCE | DIMSE (C-FIND/C-MOVE); can act as a local archive |
| Formats | JPEG2000/Lossless/JPEG-LS/RLE; SEG, RTSTRUCT, RTDOSE, GSPS, SR, PDF, WSI | Broad image support inherited from OsiriX |
| MPR / 3D | Ax/sag/cor/oblique, slab MIP/MinIP/Avg, Metal GPU volume rendering, PET/CT fusion | MPR, 3D VR — capable but aging rendering stack |
The platform row decides most cases before features even matter. If your reading happens on a Mac, Horos costs nothing and does a lot. If it needs to happen on an iPad — in a dental operatory, at a patient's bedside, on a train with a referral CD copied to the Files app — Horos is not an option, and the question becomes which iOS viewer to pick. The formats each app handles are documented in Ossidex's format reference.
Choose Horos If…
- You need a free desktop workstation on macOS and can live with an aging release cadence.
- You want open-source software for institutional, teaching, or research reasons.
- Your PACS is reachable only over classic DIMSE (C-FIND/C-MOVE) — Horos speaks it natively; Ossidex uses DICOMweb.
- You need a local archive/database on the Mac to organize thousands of studies.
Choose Ossidex If…
- You need DICOM on iPad or iPhone — Horos simply does not exist there.
- You read dental CBCT: panoramic arch reformats, cross-sections, tooth numbering, and Misch bone-density readouts are built in, not bolted on.
- You want an actively maintained viewer with a modern GPU pipeline — slab MIP/MinIP, 3D volume rendering, PET/CT fusion, side-by-side compare.
- You value the same local-only privacy model Horos users are used to: offline, no account, nothing uploaded.
Migration and Coexistence
Nothing to migrate, really — DICOM is the interchange format. Export a study from Horos as a folder, ZIP, or DICOMDIR and it opens in Ossidex as-is; AirDrop makes the Mac-to-iPad hop trivial. The tidier long-term setup is a small DICOMweb archive such as Orthanc: Horos feeds it over DIMSE, Ossidex queries it over QIDO-RS/WADO-RS, and every device sees the same library. Annotated views from Ossidex export back as DICOM Secondary Capture, so findings travel in the other direction too. Details of the rendering stack are on the technology page.
FAQ
Is there a Horos app for iPad or iPhone?
No. Horos is macOS-only and has never shipped an iOS version. If you want Horos-style DICOM viewing on an iPad, you need a different app — Ossidex is a native iOS viewer with MPR, 3D volume rendering, and PACS access.
Is Horos still maintained?
Horos remains available and usable, but development has slowed noticeably in recent years, with long gaps between releases. That matters mostly for macOS compatibility after major OS updates and for support of newer DICOM features. It is still a capable free desktop viewer.
Horos is free — why pay for Ossidex?
If an open-source macOS desktop viewer covers your needs, Horos may fit. Ossidex addresses native iPad and iPhone workflows, including dental panoramic reformats and on-device rendering. Ossidex is free to download; Apple shows optional Pro plans and regional prices before purchase.
Can Ossidex open studies exported from Horos?
Yes. Horos exports standard DICOM — folders, ZIPs, or DICOMDIR — and Ossidex opens all of these directly. Both can also point at the same DICOMweb archive (e.g. Orthanc), which is the cleanest way to share a study library between a Mac and an iPad.
Which handles dental CBCT better?
Ossidex, clearly — this is its focus. Horos displays CBCT volumes as generic CT, but has no arch-curve panoramic reformat, no tooth numbering, no implant-oriented density readout. Ossidex ships all of these plus CBCT-specific window presets.
Is Ossidex open source like Horos?
No, Ossidex is a commercial app with a free tier. What it shares with Horos is the privacy model: everything runs locally on your device, offline, with no account and no cloud upload.
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