We keep a page for .arw because it shows up in the mailbag every week. Compressed .arw from the newer bodies needs a decoder newer than the camera release.
The structure, briefly
TIFF-based with Sony maker notes; long-exposure and multi-frame noise reduction data is stored alongside the mosaic.
Sony bodies write a lens-correction table into the file, so a decoded .arw is already distortion-corrected before you touch it.
The first bytes
The check is cheap: the first 4 bytes are 49 49 2A 00. If anything else is sitting at offset 0, the file was renamed and the extension is the problem, not the file.
Opening it without the program that made it
Installed options: Sony Imaging Edge Desktop, Adobe Camera Raw / Lightroom, Capture One, Darktable, RawTherapee. None of them have to be the program that made the file: Universal Viewer reads it and writes nothing back.
Converting .arw to something usable
The targets people actually ask for are .jpg, .png, .dng, .tif. Each one has its own page with the settings that matter: arw → jpg, arw → png, arw → dng, arw → tif
Checked 2026-10-05 — M. Halvorsen.
Notes from the file library
Files of this kind are catalogued with the family named in the table above. The family groups them by what a file carries, not by the application that wrote it, which is why two extensions from the same application can sit in different families.
Two things decide whether a file can be opened on a machine that never had the application that made it: the header, which says what the container is, and the structure behind it, which says whether the contents can be read at all. The conversion guides listed on the page cover the targets that come up most often.
Format pages are rebuilt with each release of the toolset, and the review line at the bottom of the page is when an editor last checked the entry against a file. If a page disagrees with a file you have, send the first sixteen bytes and the build number to the support address and the entry is corrected in the next build.