What is a CR2 file?

CR2 is a container: a wrapper that holds streams encoded by something else. It stores a grid of pixels, so enlarging it past its own resolution softens it. It is used for photography and editing.

The extension is .cr2, and the full name is Canon Raw 2. Both matter less than what the file can hold, which is what the rest of this page is about.

Canon published it in 2004. It comes out of Canon EOS digital SLRs bodies.

Age is worth knowing here for one practical reason: the older a format is, the more programs have had time to learn it.

Reading it outside the vendor’s own software depends on work done by other people, usually by inspection rather than by documentation. That mostly works and occasionally does not, which is the reason to convert anything you intend to keep.

It still opens everywhere and is still written by older tools, but nothing new is being built around it. Convert what you mean to keep, and do not choose it for something starting today.

CR2 stores its content exactly. Saving it again changes nothing, so it can be opened, edited and re-saved as often as you like without accumulating damage — which is what makes it a working format rather than a delivery one.

CR2 has nowhere to record transparency. Anything transparent in the source is filled with a solid colour on the way in — white, unless something chooses otherwise.

Up to 14 bits per channel. It can work in RGB.

More than eight bits per channel is what stops a gradient from stepping when it is edited, which is why it matters in a working file and rarely in a finished one.

Adobe Lightroom, Canon Digital Photo Professional and darktable read it, and so do most programs of the same kind.

If a file will not open, the format is rarely the problem — it is more often that the program predates it. Converting to something older is the reliable way past that, and it is what the rest of this site is for.

No browser reads it.

That is the single most common reason to convert it: not that the format is bad, but that the place you want to show the file cannot read it.

CR2 can hold EXIF, XMP and GPS coordinates.

The GPS coordinates are the field worth thinking about before sending a file anywhere: they say where the photograph was taken, and almost nothing warns you that they are still in there.

CR2 is meant to be opened and changed. Keep the file in this format for as long as the work is going on, and export from it whenever a finished copy is needed.

The recurring complaints: programs often show an embedded preview rather than the real data and support outside its home ground is uneven.

None of these is a reason to avoid the format. They are the things worth knowing before you are surprised by one, which is a different claim and a more useful one.

CR2 is what every Canon DSLR wrote from 2004 until CR3 replaced it in 2018 — the whole Rebel line, every model from the 20D to the 5D Mark IV and the 1D X Mark II. Canon held the largest share of the camera market through that entire period.

The consequence is that CR2 is very likely the most numerous raw format in existence, and that most people opening one today are opening something old. That shapes what is worth knowing about it: not whether to shoot it, but whether the files will still open in ten years and what to do about it now.

CR2 uses TIFF’s tag structure as its foundation, as ARW, NEF and ORF do. A program that can read one has most of the machinery for the others, and the format was reverse-engineered thoroughly and early.

That is the practical difference from CR3, which abandoned the TIFF lineage for a new container and consequently went unsupported for a period after launch. CR2 has no such gap: essentially anything that reads raw at all reads CR2, including software that stopped being updated a decade ago.

Canon compressed CR2 losslessly from the beginning — the file is smaller than the raw sensor readings and identical when decompressed. On most bodies there is no quality setting and no decision to make.

The exception is sRAW and mRAW, menu options on the 1D Mark III, 5D Mark II and III, 7D and 60D, which write a downsampled and already demosaiced image into the same `.CR2`. Those aside, a CR2 is the full measurement, which is worth stating because CR3 introduced C-RAW, a genuinely lossy option, and the two are easy to conflate. In a mixed archive the CR2 files are almost always unambiguous while the CR3 files may or may not have had data discarded at the shutter press.

Early bodies recorded 12 bits per channel and later ones 14, with the transition falling around 2007 to 2009 depending on the model line. Some cameras also drop to 12 bits in high-speed continuous shooting.

Fourteen bits is 16,384 levels against 4,096, and the difference shows in the same place as always: how far shadows can be lifted before banding appears in a gradient. Both are enormously better than a JPEG’s 256, so the argument for shooting raw holds either way — it is the margin at the extremes that differs.

Support for the earliest CR2 variants — 20D, 350D, 1D Mark II — is where the long tail thins out. Most current software still reads them, but a few converters have dropped the oldest tables, and each year makes that more likely rather than less.

The practical advice for anyone with a large archive is to test rather than assume: open the oldest file in the catalogue in whatever you use now, and if it fails, that is the signal to migrate while software that can still read it exists. It is a much cheaper problem to solve early.

DNG is the documented, published raw format, and Adobe’s converter handles CR2 including old bodies. Conversion is lossless, produces files roughly 15 to 20 per cent smaller, and yields something readable by anything that reads DNG rather than by anything that happens to know Canon.

The cost is real and worth weighing. Canon’s own Digital Photo Professional will no longer open the file, so the manufacturer’s lens corrections and picture styles are out of reach. Adobe’s converter can embed the original CR2 inside the DNG as a hedge, at the price of a file larger than either alone. For an archive meant to outlast the camera, that hedge is usually worth taking.

The 5D Mark IV was the notable CR2 body offering Dual Pixel raw, recording both halves of each photosite and roughly doubling the file size. The two views differ by a fraction of a millimetre, which gives a slight parallax.

What it buys is small and specific — a minor shift in the apparent focus plane, some control over bokeh and ghosting — and it is available only in Canon’s own software. Converted anywhere else, a Dual Pixel CR2 is simply a large ordinary raw with nothing lost that anything else could have used.

Every CR2 contains a full-size JPEG preview with Canon’s processing applied — the image the camera showed on its screen. It is what a file browser displays as a thumbnail, and it is why a picture sometimes appears to change as an editor finishes loading.

For an old archive it is a genuine escape hatch. If a very old CR2 defeats your software, the embedded JPEG can be extracted and gives a usable full-resolution photograph with the look the camera intended. It carries none of the editing latitude, but it is not nothing.

To share or print, JPG at high quality. For further editing outside a raw workflow, or where every pixel must survive, PNG or TIFF. For a whole archive being future-proofed, DNG rather than either.

Keep the CR2 regardless of which you choose. The converted file has the white balance, the tone curve and the colour interpretation baked in permanently, and none of those decisions can be revisited. For photographs taken fifteen years ago and not repeatable, that matters more than the disk space.