The RW2 file (.rw2, .raw, .rwl)

RW2 is the raw format of Panasonic's Lumix cameras, from compacts and bridge cameras to the G-series Micro Four Thirds and S-series full-frame models. When a Lumix is set to RAW or RAW+JPEG, it saves an .RW2 file for each shot, next to the JPEG if you asked for both.

A raw file holds what the sensor measured, before the camera turns it into a finished picture. Each pixel on the sensor sits under a red, green or blue filter and records one brightness value. Software later works out the missing colours for every pixel (demosaicing), applies white balance, a colour profile, a tone curve, sharpening and noise reduction. A JPEG has all of that baked in; a raw file leaves it to you, with more bits per pixel to work with: most cameras record 12 or 14, against JPEG's 8.

Three things that surprise people:

• Raw files look flat when edited. The preview you first see is the camera's own JPEG. Once a raw editor renders the sensor data with its default settings, contrast and saturation can drop. Nothing is lost: the editor simply hasn't applied the camera's look yet.
• There are three extensions. Older Lumix models saved .RAW, newer ones .RW2, and some Leica cameras built with Panasonic save the same kind of file as .RWL. They're one family (see the table below).
• There's no public spec. Panasonic publishes no format documentation. Every program outside Panasonic's own reads RW2 thanks to reverse engineering, and each new camera may need a software update.

All three start with the same IIU header. ExifTool treats them as one family with the same tag table, and tells them apart by what follows the header and by the camera maker.

Not every Leica writes RWL: Leica's own designs record DNG. And a file called .raw isn't necessarily from Panasonic: other cameras and many scanners and scientific instruments use that extension too (see the RAW explainer).

To make a JPEG, open the file in any of these and export. To get only the camera's embedded preview, without developing the raw data, ExifTool can extract it:

# save the camera's own JPEG from inside the RW2
exiftool -b -JpgFromRaw P1000123.RW2 > P1000123.jpg

# list camera, lens, exposure and GPS tags
exiftool -a -G1 P1000123.RW2

The extracted JPEG is the picture the camera made, with its picture style and white balance. Developing the raw data yourself gives you more room to fix exposure and colour.

• The camera is newer than the software. Every new Lumix model needs its own colour data and sometimes decoding changes, so older versions of Lightroom, Photoshop, darktable or the Windows extension may refuse the file or show only the preview. Update the software, or convert the file with Adobe's free DNG Converter (below).
• The thumbnail is fine but editing fails. File managers show the embedded JPEG, which any JPEG decoder can read. The raw data itself needs a raw decoder that knows the camera.
• Colours look different from the camera's JPEG. Each program has its own rendering. Choose a camera-matching profile in your editor if it has one, or start from the embedded JPEG's look.
• A browser or website won't show it. Browsers can't display raw files. Export a JPEG to share or post the photo.
• A .raw file won't open in Panasonic's software. The oldest models aren't covered by SILKYPIX Developer Studio SE; use a third-party raw editor or Apple Photos.

Shoot RW2 when you expect to edit: difficult light, mixed white balance, highlights you want to recover. Use JPG or HEIC for pictures that go straight to people. Converting RW2 to DNG changes the container, not the sensor data, and makes the file readable by more software; it doesn't improve quality.

Raw files carry more metadata than most JPEGs, and it travels with the file when you send or upload it:

• Camera and lens serial numbers. Panasonic's maker notes include an internal serial number, and lens and accessory serial numbers where available. They link every photo to one camera.
• Location. Cameras with GPS, or paired with a phone app that adds location, write coordinates to the GPS directory.
• Date, time and settings, in the Exif directory and again inside the embedded JPEG, which carries its own Exif block.

Check what's there with exiftool -a -G1 file.rw2. The usual advice is to share an exported JPEG, with metadata removed in the export settings, rather than the raw file itself. Like any complex binary format, RW2 contains no scripts, but raw decoders have had memory-safety bugs; keep them updated.