History Lesson: What Is a .arw File? Sony RAW

What is a .arw file?

A .arw file is Sony Alpha RAW — the proprietary camera RAW package Sony’s Alpha digital bodies (and related ILC / compact lines that write ARW) save for later demosaic (turning the Bayer mosaic into a full-color image) and tone work. Think of it as the capture kept for editing, not a social-ready JPEG. Under the hood the bytes sit in a little-endian TIFF structure (the classic ‘II’ marker), with previews, Exif tags, and Sony MakerNotes alongside the full-dimension mosaic payload. Sensor samples are commonly 12- or 14-bit versus JPEG’s 8-bit.

Compression options evolved with the bodies. Careful technical timelines (including secondary write-ups such as the lclevy/sony_raw notes) commonly describe early ARW 1.0 as 12-bit uncompressed, an ARW 2.x wave from the A700 era (~2007+) with evolving options including visually lossy cRAW (“compressed RAW”), later 14-bit writing on some bodies, and lossless compressed options on newer high-end ILC generations often labeled in the ARW 4.x era (~2021+). Hedge exact model-first claims when sources disagree — the durable story is decades of Sony bodies writing .arw with a growing menu of bit-depth and compression choices.

Why won’t Photos or Windows open ARW?

Because ARW is camera RAW, not a finished display image. Windows Photos, File Explorer, and many browsers often have no native ARW decoder path, so the file can show a blank or generic icon even when the capture is intact. That blank preview is a missing codec / raw pipeline problem — not proof the shoot is empty. You need software that understands Sony’s TIFF-based RAW package (or a converter that turns it into JPG or PNG for everyday viewing).

ARW vs SRF / SR2 / ARQ vs DNG

Before everyday .arw, Sony’s Cyber-shot RAW lineage used different extensions. Technical secondary sources commonly place .srf with early Cyber-shot RAW such as the DSC-F828 (~January 2004) and .sr2 with bodies such as the DSC-R1 (~December 2005). Those packages are related TIFF-based cousins — not the same on-disk extension as Alpha .arw, which arrived with the DSLR-A100 (~July 2006). Renaming .srf or .sr2 to .arw does nothing useful.

ARQ is a later multi-frame / pixel-shift package on some Sony bodies (commonly cited from the a7R III era around November 2017): several shifted frames combined into a different package, not the same as a normal single-shot .arw. DNG (Digital Negative) is Adobe’s open, documented RAW container (announced 2004). Photographers often convert proprietary RAW — including ARW — into DNG for archival interchange, but that is a real conversion step. CR2 is Canon’s proprietary TIFF-based RAW; NEF is Nikon’s. Renaming .arw to .dng (or to .cr2 / .nef) does nothing useful.

Where ARW came from (Sony Alpha A100 era, ~2006)

Sony entered interchangeable-lens digital SLR photography after acquiring selected Konica Minolta digital-SLR assets (agreement announced January 2006, asset transfer around 31 March 2006), keeping A-mount continuity with the former Minolta AF / Maxxum–Dynax lens system. Sony’s first marketed Alpha DSLR, the DSLR-A100, was introduced around June 2006 for a July 2006 ship window and is widely cited as the debut of ARW 1.0 (12-bit). From there the Alpha / NEX / a7 / RX families kept writing .arw while compression and bit-depth options expanded.

Archival identification treats early ARW as TIFF-based Sony camera RAW: PRONOM fmt/191 (“Sony ARW RAW Image File 1.x”) notes the format is based upon TIFF, with signatures involving the TIFF header, a SONY maker string, and Sony MakerNote FileFormat values that distinguish ARW generations from related Sony RAW packages. That is preservation metadata — useful when a blank Windows icon makes a real capture look like nothing.

Why .arw files still sit on disks in 2026

By 2026, .arw still shows up from decades of Sony Alpha, NEX, a7, and RX shoots, wedding and travel cards, Lightroom catalogs, and “old camera still in the closet” backups. Newer bodies continue to write ARW, and the older masters remain. Windows may still show a blank icon without a raw pipeline. These are legacy files in the everyday sense: still valuable captures, often confusing next to JPEGs, and easy to leave stranded on an old drive.

Legacy File Converter converts ARW and other listed camera RAW extensions (CR2, CR3, DNG, NEF, ARW, and related family members on Supported File Types) locally on Windows to JPG or PNG. Nothing is uploaded. This article stays the history; for practical open-and-convert steps, see Opening RAW Camera Files Without the Camera Software. For neighboring RAW lessons, see History Lesson: What Is a .nef File? Nikon RAW and History Lesson: What Is a .cr2 File? Canon RAW.