The RAW file (.raw)

"Raw" means data without processing or without a wrapper, and several unrelated programs and devices chose .raw as the extension for their output. A file called something.raw is usually one of these:

• A camera raw photo from an older Panasonic or Leica camera. A real file format with a header and metadata. Panasonic later moved to .rw2 (RW2). The Kyocera Contax N Digital also wrote .raw files.
• Headerless image data: pixel values with no description of the image. Photoshop's Photoshop Raw format, scientific and industrial cameras, game terrain heightmaps and 3D scan volumes (often with a separate small header file, such as .mhd) all produce files like this.
• Headerless audio: PCM samples with no WAV header, as written by audio tools, recorders and embedded devices.
• A raw disk image: a byte-for-byte copy of a disk, USB stick or partition, made with dd or used directly by virtual machines such as QEMU.

1. 1Where did it come from? From a camera's memory card: camera raw. From a disk imaging or forensic tool, or a virtual machine folder: a disk image. From an audio or measurement program, or a scientific instrument: headerless data. The program that wrote it usually knows the parameters.
2. 2How big is it? Photos are megabytes; disk images are usually hundreds of megabytes to terabytes and a whole number of 512-byte sectors. For headerless data, factor the size: 921,600 bytes is 640 × 480 × 3 (an 8-bit RGB image) and 10,584,000 bytes is one minute of CD-quality stereo.
3. 3What does file say? On Linux and macOS, file something.raw recognises disk images by their partition table or file system. It says "data" for headerless data and for Panasonic camera RAW, so a "data" answer means you look at the bytes next.
4. 4What are the first bytes? xxd something.raw | head -4, or a hex editor. 49 49 55 00 is Panasonic or Leica camera RAW, and ARECOYK (KYOCERA backwards) at byte 25 is a Contax N Digital file. A camera make in plain text near the start also points to camera raw. Anything else with no recognisable header is headerless data.
5. 5Try ExifTool: exiftool something.raw reads camera RAW files and names the camera; for headerless data it can only report the file size.

Panasonic's early raw-capable Lumix cameras saved .raw files; later models use .rw2, and Leica's equivalents .rwl. ExifTool reads all three with the same Panasonic module. The RAW files are built like a TIFF: a header, a main directory of tags that describes the sensor data and its colour filter layout, and a link to Exif metadata. According to libopenraw, the oldest RAW files have no preview image, while some later RAW files and all RW2 files include a full JPEG with its own Exif data.

• Open them in Adobe Camera Raw or Lightroom, in Apple Photos and Preview (Apple's supported list still includes Panasonic's oldest raw models), or in Windows Photos with the Raw Image Extension, which is built on LibRaw.
• If an app ignores them, it may not treat .raw as a camera extension. Open the file from inside the app, or convert it with Adobe's free DNG Converter to DNG.
• See the camera and settings: exiftool photo.raw.

Like any camera file, these contain Exif data: camera model, date and time and settings. Check before you publish originals.

A headerless image file is only the pixel values, so you have to supply what a header would have said. Get it from the program or device that wrote the file, or work it out from the size:

# ImageMagick: 640 × 480, 8-bit RGB, interleaved
magick -size 640x480 -depth 8 rgb:photo.raw photo.png

# 16-bit greyscale, big-endian (a heightmap or a scientific image)
magick -size 1024x1024 -depth 16 -endian MSB gray:height.raw height.png

# ImageMagick 6 uses "convert" instead of "magick"

• GIMP: File > Open, then choose Raw image data under Select File Type. GIMP asks for the offset, width, height and image type, and shows a preview as you change them.
• Photoshop: opening a .raw file as Photoshop Raw asks for width, height, number of channels, interleaving, bit depth, byte order and header size; Photoshop can also save in this format.

Raw audio is a stream of samples with no header, so a player has to be told the sample format, byte order, number of channels and sample rate. Get any of them wrong and you hear noise, or the right sound at the wrong speed or pitch.

• Audacity: File > Import > Raw Data. Choose the encoding (such as signed 16-bit PCM or 32-bit float), byte order, channels, start offset and sample rate. The Detect button guesses, but its guess can be wrong. Audacity can't import raw data stored as text.
• FFmpeg: state the format before the input, then save a normal file:

# signed 16-bit little-endian, 44.1 kHz, stereo → WAV
ffmpeg -f s16le -ar 44100 -ac 2 -i sound.raw sound.wav

# 32-bit float, 48 kHz, mono → FLAC
ffmpeg -f f32le -ar 48000 -ac 1 -i capture.raw capture.flac

If you don't know the parameters, start with signed 16-bit little-endian, the most common, and check the result: a sound at the right pitch and length means the rate and channels are right; loud noise usually means the wrong sample format or byte order. The length in seconds should come out as size ÷ (rate × channels × bytes per sample).

A raw disk image is an exact copy of every sector of a disk or partition, with nothing added. That's why it's called raw, and why it's the simplest format for virtual machines and data recovery. QEMU's documentation calls it simple and easy to export to other emulators; on file systems that support sparse files, the parts of the image that were never written take no space.

# what's inside: partition table and partitions
file disk.raw
fdisk -l disk.raw

# Linux: attach read-only (it prints a device such as /dev/loop0),
# then mount a partition from it read-only
sudo losetup --find --show --partscan --read-only disk.raw
sudo mount -o ro /dev/loop0p1 /mnt

# make one from a USB stick (check the device name first!)
sudo dd if=/dev/sdX of=usb.raw bs=4M status=progress

# convert for a virtual machine, and check its real size
qemu-img convert -f raw -O qcow2 disk.raw disk.qcow2
qemu-img info disk.raw

7-Zip can open many disk images and list or extract the files in common file systems, without mounting anything. Virtual machine software such as QEMU can boot a raw image directly.