What is CR2?

How CR2 Works

CR2 stands for Canon Raw version 2, and the important word is raw: a CR2 file stores the data read almost directly off the camera's image sensor, before the camera has turned it into a finished picture. A normal JPEG is a cooked photograph, the camera has already decided the white balance, contrast, sharpening, and color, then thrown away the rest. A CR2 keeps the underlying sensor readings instead, so those decisions can be made later on a computer with far more control and no loss of information.

Physically, a CR2 is built on the TIFF container structure. Inside that wrapper it holds several things at once: a small embedded JPEG preview so the camera and file browsers can show a thumbnail quickly, the full-resolution sensor data, and a large block of metadata describing the exposure, lens, and camera settings. The sensor data itself is usually stored with lossless compression, so the file is smaller than a completely uncompressed dump but still contains every original measurement.

The sensor data is not a normal color image yet. Most Canon sensors sit behind a Bayer color filter array, a checkerboard of red, green, and blue filters, so each pixel site records only one color channel. Turning that mosaic into a full-color photo requires demosaicing, a reconstruction step that interpolates the missing colors at every pixel. Because a CR2 delays this step, the software you edit in, rather than the camera, controls how it is done, which is a large part of why raw files look cleaner when processed well.

Keeping the data raw is what gives CR2 its editing headroom. The file typically records 12 or 14 bits per channel rather than the 8 bits of a JPEG, so there is far more tonal information in shadows and highlights. That extra depth is why you can recover a blown sky or lift a dark foreground from a CR2 with little visible damage, edits that would band or fall apart badly on an already-compressed JPEG.

History and Standardization

CR2 was introduced by Canon in the mid-2000s as the raw format for its digital SLR cameras, replacing the earlier CRW format. It served as the standard Canon raw format for roughly a decade across a very large range of EOS bodies, which is why CR2 files are extremely common in photo archives from that era.

CR2 is a proprietary format. Canon never published a full public specification, so the exact meaning of every field was reverse-engineered by the open-source community, most visibly through tools like dcraw and its successors and the ExifTool metadata project. This worked well enough that virtually every serious photo editor can read CR2, but it is a reminder that support depends on third parties decoding a format they were not handed.

In 2018 Canon began moving to a newer raw format, CR3, built on a more modern container and offering more efficient compression. CR2 remains fully supported by editing software and is not going away, but it is now a legacy format: new Canon cameras produce CR3, while the enormous existing library of CR2 files continues to be read and archived.

CR2 Compared to DNG and JPEG

Against JPEG, the trade-off is the classic raw-versus-cooked one. CR2 files are several times larger and cannot be viewed or shared without processing, but they preserve the full sensor data and the entire editing latitude that comes with it. JPEG is finished, small, and universal; CR2 is a digital negative you develop yourself. Serious photographers shoot CR2 to keep their options open and export JPEGs only at the final step.

Against DNG, Adobe's open raw format, the difference is openness and longevity rather than image quality. A CR2 converted to DNG carries the same sensor data, but DNG is a published, standardized container designed to stay readable for decades, whereas CR2 depends on Canon-specific decoding. Many archivists convert CR2 to DNG for long-term storage for exactly this reason, though doing so means stepping outside Canon's own toolchain.

One practical point ties it together: a CR2 is only as useful as the software that can decode it. Because it is proprietary and tied to specific camera models, a brand-new camera's raw files sometimes cannot be opened until editors publish an update. That dependency, more than any quality concern, is the main argument for converting important CR2 files to an open format if you intend to keep them for the very long term.