The Sony SR2 file (.sr2, .srf)

Before Sony made interchangeable-lens cameras, it offered raw capture on a few Cyber-shot models. The DSC-F828 and DSC-V3 wrote SRF (Sony Raw Format) files. The DSC-R1, a 10-megapixel camera with a fixed zoom lens and an unusually large APS-C sensor, announced in 2005, wrote SR2. When Sony launched its Alpha range with the DSLR-A100 in 2006, it introduced ARW, and no new camera has written SR2 or SRF since.

Like any raw file, an SR2 holds what the sensor recorded: one brightness value per photosite, each behind a red, green or blue filter, before demosaicing, white balance and the tone curve turn them into a picture. Opened in a raw editor, it looks flatter than the camera's JPEG at first, and gives far more room to fix exposure and colour.

Most camera raw formats are undocumented. Sony's early formats went a step further and encrypted parts of the file, so that only software that knew the scheme could read them:

The encryption didn't keep other software out. Dave Coffin worked out the algorithm and put it in dcraw, the open-source decoder that much raw software was built on, and ExifTool, LibRaw and Adobe all read the files. In its notes on camera raw formats, the Library of Congress mentions a case where encrypted data elements forced people to use the manufacturer's own software, and treats undocumented raw formats as a preservation risk: a file that depends on reverse-engineered decryption stays readable only as long as someone maintains that code.

These cameras are two decades old, but their files still open in mainstream software:

• Mac, iPhone and iPad: Apple's list of supported raw cameras still includes the DSC-R1 and DSC-F828, so Photos and Preview open their files.
• Windows: install Microsoft's free Raw Image Extension (built on LibRaw) for thumbnails and viewing in Photos.
• Adobe Lightroom and Photoshop: Camera Raw reads both. When the DSC-R1 dropped off Adobe's printed camera list in 2021, users confirmed that Lightroom Classic still opened its files.
• Free: darktable and RawTherapee, which rely on open-source decoders that have long supported these cameras.
• Not Sony's current software: Imaging Edge lists ARW, ARQ and AXR as its raw formats, not SR2 or SRF.

# show the deciphered white balance and other private tags
exiftool -a -G1 -SR2SubIFD:all DSC00001.SR2

# save the embedded preview
exiftool -b -PreviewImage DSC00001.SR2 > DSC00001.jpg

Old raw formats only stay readable while someone maintains a decoder. If you have an archive of R1 or F828 photos, three steps protect it:

1. 1Keep the originals. Nothing replaces the camera's own file.
2. 2Make DNG copies with Adobe's free DNG Converter. DNG has a public specification and an ISO standard, and the converter can embed the original raw file inside the DNG, so nothing is lost.
3. 3Export finished photos as 16-bit TIFF or high-quality JPG for anything you'll want to look at without a raw editor.

SR2 and SRF files carry the date and time, all camera settings and a camera model identifier. Check with exiftool -a -G1 file.sr2 before publishing a collection, including for location or captions that other software may have added later, and don't strip all metadata from the raw files themselves: converters need the private Sony data to render the colours.