Pentax PEF raw files that will not open on a Mac

A Pentax PEF file that will not open on a Mac is usually intact. macOS adds raw support one camera at a time through system updates, so a PEF from a body your version of macOS does not know can show a thumbnail in Finder and still refuse to open in Preview or Photos. Update macOS first. If that does not help, develop the photos in the camera, or set the camera to record DNG instead, a choice most camera makers do not offer.

Why a PEF shows a thumbnail and nothing else

A PEF holds two things: the data from the sensor, and a JPEG preview that the camera made for its own screen. Finder and Quick Look can show that preview without decoding any sensor data. So a thumbnail proves the file arrived in one piece, and says nothing about whether the Mac can develop it.

Developing the sensor data takes a profile for that exact camera: its sensor layout, its color response and its compression. Until macOS has that profile, the Mac can show the cover of the picture and cannot open it.

One feature raises the odds of trouble. Pixel Shift Resolution, found on many Pentax bodies, takes four exposures and stores them together in one raw file. Those files are much larger than an ordinary PEF, and software that does not know the feature tends to develop only one of the four exposures, or to refuse the file.

Test whether your Mac can decode the file

Preview is the simple test: if the photo opens at full size, the Mac can read it. For a definite answer, open Terminal and run:

sips -g pixelWidth -g pixelHeight ~/Pictures/IMGP1234.PEF

If sips prints the pixel dimensions, the raw decoder worked. If it prints an error, macOS could not decode the file, whatever the thumbnail suggests.

If only some files fail, check for a short copy. Put the folder in list view in Finder and sort by Size. PEF files from one camera vary with the scene, so only a dramatic difference means anything, but a file far smaller than its neighbors was probably cut off while it was being copied. Copy it again from the card, with a different card reader if the first one keeps failing.

The fixes, in order

1. Update macOS. Open System Settings, General, Software Update. Support for new cameras ships inside system updates, and this resolves most cases.
2. Check Apple’s list. Apple publishes a support page listing the cameras whose raw files macOS can read. Compare the exact model name, since bodies with similar names are separate entries.
3. Develop in the camera. Put the card back in the camera, press playback, and choose RAW Development from the playback menu. The camera applies its own color settings and saves a JPEG to the card. It is slow for a whole shoot and ideal for the handful of photos that matter.
4. Use the software that came with the camera. Pentax supplies raw software for the Mac that understands its own cameras’ files and exports JPEG or TIFF.
5. Convert the files to DNG. A DNG converter rewrites the raw data into an openly documented format, which macOS can usually read without knowing the camera.

Set the camera to DNG for next time

Pentax cameras are unusual in letting you choose the raw format. In the camera’s image capture settings, the RAW File Format option offers PEF or DNG. Both hold the same sensor data. DNG is openly documented, so far more software reads it, and a Mac that has never heard of the camera can usually still open the file.

If you move between computers, or keep a Mac on an older version of macOS, switching to DNG removes this problem for every photo you take from now on. It does nothing for the PEF files you already have. Those need one of the fixes above.

Converting PEF to JPEG once the Mac can read it

Preview, one photo. Open the PEF, choose File, Export, set Format to JPEG and save.

Preview, several photos. Open them together so they share one window, select the thumbnails in the sidebar, and choose File, Export Selected Images. Click Show Options to set the format.

Finder, a handful. Select the files, right-click, and choose Quick Actions, Convert Image. Pick JPEG and a size.

Manatee, a whole shoot. Manatee converts a folder in one drop. Open it, choose Convert, drop the folder in, and pick JPEG, PNG, HEIC or TIFF. Each result is written as a new copy beside its original, and the PEF is never modified. Nothing is uploaded and no account is needed; it all runs on the Mac. It is free for 24 hours with every feature, then $9 once.

Two honest limits. Manatee converts the PEF files your Mac can decode. It does not add support for a camera that macOS does not know yet, so sort that out first with the steps above. And it is not a raw editor: there is no exposure slider, no white balance control and no lens correction.

For raw formats in general, see how to convert RAW photos to JPEG on a Mac. If you want a TIFF to edit instead of a JPEG to share, how to convert a DNG raw photo to TIFF explains what that format keeps.

Why the converted photo looks flatter than the camera’s version

The picture on the camera’s screen, and the JPEG the camera saves, have a Custom Image setting applied: the camera’s own recipe for color and contrast, such as Bright or Landscape. The raw data carries none of that. macOS develops it with a neutral default, so the result often looks less saturated and less punchy than you remember.

Nothing has gone wrong. You can develop the favorites in the camera to get its look, or adjust the converted photo in Photos afterwards. A photo that looks dull after converting it covers the other reasons a conversion can lose its color.

Questions

Should I shoot PEF or DNG? For compatibility, DNG. Both record the same sensor data, and DNG opens in more places. Keep PEF only if software you rely on asks for it.

Can I rename a .PEF file to .DNG? No. The extension is a label, and the two formats are structured differently inside. A renamed file fails in the same places, and sometimes in more. Changed a file extension and now it will not open explains why.

Does converting to JPEG lose anything? Yes. A JPEG keeps 8 bits per color channel and compresses the picture, so the extra highlight and shadow detail in the raw file is not carried over. Treat the PEF files as your originals and the JPEGs as copies for sharing.

The thumbnail looks fine. Can I just use that? The embedded preview is a real JPEG, but it is often smaller than the full photo and more heavily compressed. It will do for identifying a shot, not for printing.