What Is an ARW File? Sony's RAW Format, Explained
An ARW file — short for Alpha RAW — is the RAW photo format written by Sony Alpha cameras. It is not a finished image. It is the unprocessed data from every photosite on the sensor at the moment you pressed the shutter, plus the camera's metadata and a JPEG preview, packed into one .ARW file. Think of it as the digital negative: everything the camera saw, before anyone decided what the photograph should look like.
That one distinction — data, not image — explains almost everything people find confusing about ARW files: why they need special software, why they look flat next to the camera's JPEG, and why they're ten times the size. Here's the rest.
ARW at a glance
| Full name | Sony Alpha RAW |
|---|---|
| Extension | .ARW |
| What it holds | Unprocessed sensor data, EXIF metadata, embedded JPEG preview |
| Structure | Based on TIFF, like most camera RAW formats |
| Bit depth | Typically 14-bit (16,384 tonal levels per channel, against a JPEG's 256) |
| Typical size | 25–130 MB depending on megapixels and compression setting |
| Opens with | macOS Preview and Photos, Sony Imaging Edge, and RAW editors such as RevelRaw, Lightroom or Capture One |
What's actually inside an ARW file
A camera sensor doesn't record a picture. Each photosite records how much light hit it through a single-color filter — red, green or blue — arranged in a mosaic. An ARW file stores those readings as they came off the sensor:
- The mosaic sensor data. One brightness value per photosite, at 14-bit precision. No white balance, no sharpening, no color profile has been applied yet. Turning this mosaic into a viewable photograph — called demosaicing — is the job of your RAW editor.
- Metadata. Camera body, lens, exposure settings, focus points, and the picture profile you had dialed in. Editors read this to know how to interpret the data; nothing in it is baked into the pixels.
- An embedded JPEG preview. The camera develops a small JPEG with its own processing and tucks it inside the ARW. This is what you see on the camera's screen and in Finder thumbnails — which is why a RAW file can look one way as a thumbnail and another once an editor opens the real data.
Why an ARW looks flat next to the camera's JPEG
When you shoot JPEG, the camera develops the photo for you: it picks a white balance, boosts contrast and saturation, sharpens, and throws away the data it no longer needs. When you shoot RAW, all of those decisions are still yours to make. So when an editor first opens the ARW with neutral settings, you're seeing the undeveloped negative — flatter, softer and duller than the confident JPEG the camera showed you. That's not lost quality. It's headroom: the highlight detail, shadow depth and color latitude the JPEG would have discarded are all still in the file, waiting for your version of the photograph. Our RAW vs JPEG guide shows exactly what that headroom rescues.
How big ARW files get, and why
Recent Alpha bodies offer up to three RAW compression settings, and the size difference is real. Rough figures for a 33-megapixel body like the a7 IV:
| Setting | Approx. size | Trade-off |
|---|---|---|
| Compressed | ~35 MB | Smallest; discards a little data in ways you'll almost never see |
| Lossless Compressed | ~45 MB | Every bit preserved, shrunk like a ZIP; the sweet spot where available |
| Uncompressed | ~70 MB | Every bit preserved, no shrinking; fills cards fastest for no visible gain |
Higher-resolution bodies scale up from there — a 61-megapixel a7R V writes uncompressed files over 120 MB. A JPEG of the same scene runs a tenth of the size, because it keeps only one finished interpretation and throws the rest away.
One more thing: ARW isn't frozen
Sony has revised the format across camera generations, which is why software sometimes lags the cameras. When a new Alpha body ships, Apple has to add its files to macOS before Preview and Photos will open them, and every RAW editor has to update its own support. If your brand-new camera's files won't open, the file isn't broken — your software just hasn't met that body yet. The fixes are in our guide to opening ARW files on a Mac.
How to open and convert ARW files
On a Mac you already have the basics: Preview and Photos open ARW files from most Sony bodies, and can export them to JPEG when something refuses the RAW — the full walkthrough is in our ARW to JPEG guide. To actually develop the file rather than just view it, you need a RAW editor. RevelRaw is ours: a native macOS editor built only for Sony Alpha, with its own ARW pipeline, AI scene detection that ranks 40+ presets against your photo, and the standard fine-tune controls. Everything runs on your Mac; no file ever leaves it.
Should you keep your ARW files?
Yes, for any photograph you might care about again. The ARW is the negative; every JPEG you export from it is one interpretation, fixed forever at the settings you chose that day. Keep the ARW and you can return in five years — with better taste, better software, or a client who suddenly needs a print — and develop it again from everything the sensor recorded. Storage is cheaper than a reshoot.
FAQ
What does ARW stand for?
Alpha RAW — Sony's RAW format, named for its Alpha camera line. Every Alpha body set to shoot RAW writes .ARW files.
Is an ARW file better than a JPEG?
It holds far more data — 14-bit tonal depth against JPEG's 8, with nothing baked in — so it survives editing a JPEG can't. But it isn't a finished image and needs software to develop it. If you need files that are done straight out of the camera, JPEG is the honest choice.
How do I open an ARW file?
On a Mac, double-click it: Preview handles files from most Sony bodies. Files from a just-released camera may need to wait for a macOS update, or use an editor with its own decoder, such as RevelRaw. On Windows, Sony's free Imaging Edge reads them.
Why are ARW files so big?
They store what every photosite on the sensor recorded, at 14-bit depth. A 33-megapixel body writes roughly 35 to 70 MB per file depending on the compression setting.
Can I delete ARW files after converting to JPEG?
You can, but the JPEG holds only one interpretation of the shot. Delete the ARW and you can never re-edit with more latitude than that JPEG allows. Keep the negatives.
See what's really in your ARW files. Download RevelRaw, drop one in, and watch it ranked against 40+ presets in seconds — with one full-quality export on the house. Get it on the Mac App Store.
Related reading: How to open ARW files on a Mac · How to convert ARW to JPEG · RAW vs JPEG on a Sony Alpha