CR2 - Canon Raw Version 2

A CR2 file is a raw photograph from a Canon camera. Raw means the file is not a finished picture but the sensor's own reading of the light, kept almost untouched so exposure, white balance and colour can be decided afterwards in software. Canon calls it Canon Raw version 2. It replaced the earlier CRW format and was used across many generations of EOS cameras; Canon's newer bodies write CR3 instead. Canon has never published a full specification, so support outside Canon's own software rests on reverse engineering.

How a CR2 stores its data

A CR2 is built on TIFF, the tag-based image format: the file is a set of directories, each listing numbered tags that point at the data they describe.

A single CR2 normally contains more than one image: a JPEG preview so viewers and the camera's screen have something to display immediately, a small thumbnail, and then the real payload, the sensor data, packed with a lossless compression scheme derived from JPEG, so nothing is discarded.

The sensor data is a mosaic rather than a photograph: each light sensor sits under a red, green or blue filter and records a single brightness value, so a program has to interpolate the two missing colours at every position, a step called demosaicing. The values carry more precision than a JPG's eight bits per channel, and that headroom is the whole reason to shoot raw: it lets you rescue a dark corner or a nearly blown sky. Everything the camera was set to, including picture style, white balance and lens corrections, is recorded as a note rather than applied, which is why Canon's software can show the shot exactly as the camera intended while another program shows something flatter.

What metadata a CR2 carries

A lot, and unusually much of it is Canon's own: alongside the standard fields, a CR2 carries a large private block called a MakerNote, and that is where it gets interesting.

• Standard TIFF and EXIF fields: Make and Model, DateTimeOriginal, ExposureTime, FNumber, ISOSpeedRatings, FocalLength, LensModel, Flash and Orientation.
• GPS tags with latitude, longitude and altitude, when the body has a receiver or was paired with a phone or GPS accessory.
• The Canon MakerNote, which records things standard EXIF has no field for: the camera's serial number, an owner name if one was typed into the camera, the lens serial number, the firmware version, the internal image number or shutter count, the autofocus points selected, the focus distance, the camera temperature, the picture style and custom function settings, and the in-camera white balance and lens corrections.
• An embedded preview, a separate picture from the raw data, which may not match the current edit.

Several of those are genuinely personal. The serial number ties every photo to one camera body. The shutter count acts as an odometer, which is why buyers of second-hand bodies read it from a sample file. An owner name is a name, and GPS coordinates are a place.

One practical detail: because CR2 is undocumented, most editing software will not write into it. Ratings, keywords and develop settings are saved instead in a separate XMP sidecar file with the same name, next to the CR2. If your ratings disappear when you move a photo, the sidecar was left behind; and a CR2 handed to someone else may carry none of the descriptive metadata you added.

When to use CR2

You do not really choose CR2; the camera does. What you choose is whether to keep it. Keep it when the picture matters: raw gives you exposure and white-balance latitude a JPG cannot, and a better converter released years later can get more out of the same file. Shoot JPG when you need finished pictures immediately and in volume.

The real decision is CR2 against DNG for storage. Canon's own software understands every field in a CR2, including maker-note settings other programs ignore, and the file stays exactly as the camera wrote it. DNG is openly documented, describes itself to any converter, is often smaller, and keeps edits and keywords inside the file, but converting can obscure some Canon-specific extras. Archiving the original CR2 and converting copies as needed avoids having to choose.