The ARW file (.arw)

ARW is the raw format of Sony's interchangeable-lens cameras, from the 2006 DSLR-A100 and the later SLT models to the E-mount α7, α9, α1 and ZV series, and of Cyber-shot compacts such as the RX100 and RX10 series. Sony took over Konica Minolta's camera business, and the first ARW files still carried a block in the layout of Minolta's MRW raw format. Before ARW, a few Cyber-shot cameras used the SR2 and SRF formats.

Like every raw format, an ARW keeps the readings of the sensor's photosites, each behind a red, green or blue filter, before the camera demosaics them into full-colour pixels, sets the white balance, applies its Creative Look or picture profile and compresses the result to JPEG or HEIF. Those steps happen later, in software, with your choices instead of the camera's.

• 14 or 12 bits per photosite in an uncompressed file, against 8 bits per channel in a JPG, which leaves room to lift shadows and recover highlights.
• Flat at first sight. A raw developer starts from neutral settings, so an ARW looks less punchy than the camera's own JPEG.
• Previews inside. Each ARW carries JPEG previews for the camera screen and thumbnails. Quick viewers often show those instead of rendering the raw data.
• Always 3:2. Sony's help guides note that raw images keep the full 3:2 frame even when the camera's JPEGs are set to another aspect ratio.

Sony cameras offer up to three raw file types. The names in the menu are Sony's; which ones you get depends on the model and its firmware:

How the classic compressed format works was described by the makers of RawDigger, a raw analysis tool. The raw values first go through a tone curve that reduces them to 11 bits. Each row is then cut into blocks of 16 same-coloured pixels, and each block is stored in 16 bytes: the brightest and darkest values with their positions, and 14 seven-bit offsets between them. If a block's values span less than 128 levels, nothing more is lost than the tone curve already took. If it spans more, the offsets are rounded to steps of 2, 4, 8 or 16.

The .arw extension hasn't changed since 2006, but the layout inside has. ExifTool reads the version from the FileFormat tag in the maker notes:

Software matches cameras, not versions, so the version mostly matters to developers of raw decoders. Two related files are worth knowing:

• ARQ: the result of Sony's Pixel Shift Multi Shooting, where the camera takes several shots while moving the sensor and Imaging Edge combines them into one file with full colour at every pixel. ExifTool lists it as a Sony pixel-shift raw format. Fewer programs open ARQ than ARW.
• SR2 and SRF: Sony's raw formats before ARW, from the Cyber-shot DSC-R1, DSC-F828 and DSC-V3. See the SR2 guide.

• Sony Imaging Edge Desktop (free, Windows and macOS): Sony's viewer, raw developer and remote-shooting app in one. Its Viewer and Edit parts open ARW and ARQ files and apply Sony's own processing. It's also the tool that builds Pixel Shift composites.
• Adobe Lightroom, Lightroom Classic and Photoshop (Camera Raw); Capture One; DxO PhotoLab; Affinity Photo.
• Free and open source: darktable and RawTherapee, on Windows, macOS and Linux.
• Just looking: Photos and Preview on a Mac or iPhone, for cameras on Apple's supported raw list; Windows Photos and File Explorer after installing Microsoft's free Raw Image Extension (Windows 10 version 1903 or later), which is built on LibRaw.

# save the embedded JPEG preview, no raw processing
exiftool -b -PreviewImage DSC00001.ARW > DSC00001.jpg

# which raw type and format version is this?
exiftool -SonyRawFileType -FileFormat DSC00001.ARW

# render the raw data with darktable's command-line tool
darktable-cli DSC00001.ARW DSC00001.jpg

To share or archive, export JPEG or TIFF, or convert to DNG with Adobe's free DNG Converter, which also lets older versions of Lightroom and Photoshop open files from newer cameras.

• Your software is older than the camera. Each new body needs support added, even when the version number inside barely changes. Adobe says it adds new cameras about every month or two and that cameras released in the last 90 days may need to wait. Update, or convert with Adobe DNG Converter.
• A raw type the app doesn't handle. If uncompressed files from the same camera open but lossless or M and S files don't, the app supports the camera but not that raw type. Update it, or switch the camera to another raw type.
• It's an ARQ, not an ARW. Pixel Shift composites need Imaging Edge or an app that supports ARQ.
• Colours look off, or different from the camera. The app renders the data with its own profile. Choose a camera-matching profile, or develop in Imaging Edge to get Sony's processing.
• Only a small image appears. The program showed the embedded preview, or treated the file as a plain TIFF.

Recent Sony cameras can shoot HEIF alongside or instead of JPEG. Neither is a substitute for raw when you plan to edit: white balance and highlights are fixed once the camera has processed the photo.

An ARW can't run code. Its metadata is the thing to check before sending raw files to strangers:

• Camera serial numbers in the Exif data and maker notes, which link every photo to one body.
• Location, if the camera took it from a phone over Bluetooth or another source.
• Copyright and artist names set in the camera menu, plus dates, lens and all settings.

See it all with exiftool -a -G1 file.arw. Remove GPS with exiftool -gps:all= file.arw. Don't strip every tag from a raw file: the maker notes and SR2 data are needed to develop it. Share an exported JPEG with metadata removed when that matters.