What Is an ARW File? Sony's RAW Format Explained
An .ARW file is Sony Alpha RAW — the unprocessed sensor data from a Sony camera, stored in a structure derived from TIFF/EP, the same standard several other manufacturers build on.
As a container it is unremarkable. What makes ARW worth reading about is that Sony gives you more compression choices than most manufacturers, and that the camera sometimes changes bit depth without telling you.
Three kinds of ARW
Recent Sony bodies offer uncompressed, lossless compressed and compressed RAW, and they are genuinely different files.
Uncompressed is the largest and simplest: every sample written out at full precision. Lossless compressed applies reversible compression, producing files roughly 40–60% smaller that decode to exactly the same data — there is no image-quality reason to prefer uncompressed over it, and newer bodies offer size variants of it too.
Compressed RAW is the lossy option, and it is the one with a reputation. Sony's scheme groups neighbouring pixels and stores them with a shared exponent and reduced precision, which is efficient and almost always invisible — but around very high-contrast edges it can produce faint banding or posterisation that survives into the final image. Astrophotographers and anyone recovering deep shadows next to bright highlights are the people who notice.
- ·Uncompressed — largest, no compression artefacts, no advantage over lossless
- ·Lossless compressed — the sensible default on bodies that offer it
- ·Compressed — smallest, lossy, occasional edge artefacts under heavy recovery
The 14-bit to 12-bit drop
This is the ARW behaviour that surprises people, because nothing on screen announces it. On many Sony bodies, certain modes reduce RAW bit depth from 14 to 12: continuous shooting at high frame rates, silent/electronic shutter on some models, long-exposure noise reduction, and bulb mode among them. Which modes trigger it varies by body and firmware.
Twelve bits is 4,096 levels per channel against 14 bits' 16,384. In a normally exposed frame you will not see the difference. In a deep shadow lift of several stops — exactly what you do with an underexposed frame — the coarser steps show up as banding in smooth areas.
The practical response is not to avoid those modes but to know when you are in them, and to expose so that shadows do not need rescuing when you are.
Working with ARW files
Support is broad: Lightroom, Camera Raw, Capture One (which has a particularly close relationship with Sony files), DxO PhotoLab, Affinity Photo, RawTherapee and darktable all read ARW. Sony's own Imaging Edge is free and handles the newest bodies first.
The recurring compatibility problem is not the format but the body. Each new sensor needs its own profile and decoding parameters, so a camera released last month may not open in software that is otherwise current. Waiting for a point release, or converting to DNG in the meantime, are the two options.
ARW files carry the usual EXIF, plus Sony's Creative Style and any in-camera corrections as metadata that third-party converters may or may not choose to apply.
Frequently asked questions
Which ARW compression should I use?
Lossless compressed, on any body that offers it. It is meaningfully smaller than uncompressed and decodes to identical data, so uncompressed buys nothing. Choose lossy compressed only when card space or buffer depth genuinely constrains the shoot.
Is Sony's compressed RAW actually a problem?
Rarely, and only in specific conditions: very high-contrast edges combined with heavy exposure recovery. Ordinary photographs graded normally show nothing. The reason it has a reputation is that the situations where it does show — night skies, backlit subjects pulled up several stops — are the ones people scrutinise most closely.
How do I tell whether a file is 12-bit or 14-bit?
The camera does not display it, but a metadata reader will show the bit depth recorded in the file. If it reads 12 and you expected 14, check whether you were in continuous drive, silent shutter, bulb or long-exposure NR — those are the usual causes.
Why won't my software open a new Sony camera's ARW files?
Because ARW is not one format but a family, and each new sensor needs decoding support added. Update your converter; if the body is very new, use Adobe's free DNG Converter as a stopgap, which produces a DNG almost anything can read.
Are ARW and A7R IV/A1 files the same format?
Same extension, different internals. Sony has revised the ARW structure several times, and newer bodies also introduced additional lossless-compressed size options. This is why extension alone never guarantees a file will open.
Drop an ARW into RawCut's metadata reader to see its bit depth, compression and full EXIF — locally, with nothing uploaded.
Inspect an ARW