Lossless Sony ARW.
Pretends to be a JPEG.

Which cameras

The codec does not look at the model name. It accepts Sony ARW whose raw strip is uncompressed 14-bit, 16-bit aligned, at EOF — the camera menu item RAW File Type → Uncompressed. Sony’s lossy “Compressed RAW” and lossless-compressed ARW 4.0 are refused.

Tested

Sony α7R III (ILCE-7RM3). The rates and fixtures on this page are from that body: 8000×5320, ~82 MiB per file.

α7R III

MENU → Camera Settings 1 → RAW File Type → Uncompressed. Single-shot and continuous stay 14-bit. BULB and Long Exposure NR drop to 12-bit and will be refused.

Same format

α7R II–VI, α7 II / III / IV, α7C / C II / CR, α7S II / III, α9 / II / III, α1 / II, α99 II, RX1R II / III, ILX-LR1 — when Uncompressed is selected and the file stays 14-bit.

Will not encode

Original α7 / α7R / α7S and most APS-C (compressed RAW only). α6700 (lossless compressed, no uncompressed option). 12-bit files from BULB, Long Exposure NR, or silent shooting on some older bodies.

Compression rates

Ten uncompressed Sony ILCE-7RM3 files, 8000×5320, 14-bit samples in 16-bit words (~82 MiB each). Same Bayer-delta + byte-shuffle + zstd pipeline this codec uses. Each file compressed on its own. Decode is bit-identical. Noisy or high-ISO frames shrink less; other bodies will differ.

Range on this set: 43.9%–52.3% smaller at level 19. Drop a file above to measure yours.

Compared with other lossless options

Same file: OCT00527.ARW, 81.90 MiB, uncompressed ILCE-7RM3. Generic tools were given the whole ARW. CompressARW first does a Bayer same-channel delta and a byte-shuffle of the 14-bit strip, then zstd — and still leaves a JPEG that Finder and exiftool can read. JPEG XL here is the mosaic strip only; the TIFF header would still need storing.

Not the same job

This tool only accepts uncompressed 14-bit ARW. Sony’s in-camera compressed and lossless-compressed modes are refused. zip is lossless but you cannot preview or grep EXIF until you unpack.

How a .ARWC.JPG is laid out

The container is a normal JPEG with an ARWZ trailer after FF D9. You can range-request the leading preview. The raw is not required to view the file or to read EXIF.

Input

Uncompressed Sony ARW, 14-bit, 16-bit aligned, raw strip at EOF. Sony lossy compressed RAW and lossless-compressed ARW 4.0 are refused.

Rates

About half the original on uncompressed 42 MP A7R III files. Ten-file set: 817 → 414 MiB at zstd 19 (49% smaller); level 9 is ~2 MiB larger per file.

Preview / EXIF

Bytes 0 .. EOI only. Typically under 1 MiB. HTTP Range works.

Transform

Per-row same-channel left deltas on the CFA, then low/high byte planes, then zstd (level 19 on the CLI, 9 in WASM).

Roundtrip

Encode then decode must match the original file hash. Fixtures live in CompressARWTestData.

CLI, library, WASM, desktop

One crate. Default build is the CLI. WASM is a feature flag. The Electron viewer opens a folder of .ARW / .ARWC.JPG, shows the camera JPEG, and compresses or decompresses with the arrow keys.

compress-arw encode  OCT00527.ARW
compress-arw preview OCT00527.ARWC.JPG -o preview.jpg
compress-arw decode  OCT00527.ARWC.JPG -o OCT00527.ARW
compress-arw info    OCT00527.ARWC.JPG

use compress_arw::{decode, encode, extract_preview};

let jpg = encode(&arw_bytes)?;
let jpeg = extract_preview(&jpg)?;
let arw = decode(&jpg)?;

wasm-pack build --release --target web \
  -- --no-default-features --features wasm

encode(arw, level)
decode(file)
extract_preview(file)
preview_bytes(file)

cd electron
npm install
npm start

← → browse · C compress
D decompress · O open folder