Why your Nikon .NEF files are triggering a warning banner, and how to fix it at the camera.
The Key Point: Kestrel can't yet decode Nikon's High Efficiency (HE / HE*) RAW compression. When it hits one, it falls back to the small embedded JPEG preview instead of the real sensor data — so quality scores, sharpness detection, and highlight recovery all get noticeably worse. Switching your camera to Lossless compressed or Compressed fixes it going forward.
What's happening
Newer Nikon mirrorless bodies (Z6 III, Z8, Z9, Zf, and others) offer a RAW compression option called High Efficiency (HE) and High Efficiency* (HE*). It's not a standard RAW compression scheme — it uses TicoRAW, a proprietary codec licensed from intoPIX, and reading it requires a license Nikon hasn't made available to open-source libraries.
Kestrel's analysis pipeline relies on LibRaw, the open-source library nearly every non-Nikon photo tool uses to decode RAW files, and LibRaw cannot decompress HE/HE* data. When Kestrel opens one of these files, it can read the container but not the actual sensor data, so it falls back to the small embedded JPEG preview that every NEF carries for the camera's rear LCD.
That fallback keeps Kestrel working rather than failing outright, but the embedded preview is:
- Lower resolution than the real sensor capture
- Already compressed and (usually) already sharpened in-camera
- Missing the highlight/shadow recovery headroom RAW data provides
The result is quality scores, sharpness detection, and species classification that are all working from noticeably worse source data — through no fault of your shot.
How to fix it
Switch your camera's RAW compression setting away from High Efficiency:
- On your camera, open the Photo Shooting Menu
- Find NEF (RAW) recording → NEF (RAW) compression (menu wording varies slightly by model)
- Choose Lossless compressed (recommended) or Compressed instead of High efficiency / High efficiency*
- Re-analyze any affected folders in Kestrel — LibRaw fully supports both of these formats, so you'll get full-resolution analysis
Lossless compressed produces larger files than HE/HE*, but every byte of sensor data survives, which is what Kestrel (and most other photo software) needs.
Do I need to re-shoot anything?
No. This only affects future shots. Photos you've already taken in HE/HE* will keep triggering the fallback — there's no way to recover sensor data that was never captured — but everything else about your workflow is unaffected. Kestrel will just keep flagging them so you know those particular results are less reliable.
Will Kestrel support HE/HE* eventually?
Possibly, once the TicoRAW licensing situation changes for LibRaw — that's outside Kestrel's control. A few commercial tools (Topaz Photo AI, Affinity Photo) have added HE/HE* support through separate SDKs; if that becomes broadly available Kestrel will revisit it.
Still stuck?
Please use the feedback button in Kestrel, or contact me directly — mention your camera model and that you're seeing the "unsupported compression type" banner.