Convert CR3 to TIFF

Open a CR3 in a hex viewer and the fifth byte begins the word "ftyp", followed by the brand "crx". That is the ISO base media file format — the same box-and-atom structure that carries MP4 video and HEIF images — and it is a completely different shape of file from CR2, which Canon built on TIFF and which therefore looked at least superficially familiar to anything with a TIFF parser.

Canon changed containers with the EOS R generation in 2018 and did not publish the specification. Third-party support had to be reverse-engineered, which is why it took Adobe, darktable, dcraw’s successors and everyone else a considerable time to arrive, and why software that stopped receiving updates before then will never read one. An old Photoshop reporting a CR3 as an unknown format is telling the truth about itself rather than about the file.

TIFF has been readable by everything since 1986. Not modern TIFF with clever compression and layers, but the plain uncompressed baseline: a header, a directory of tags and a block of RGB pixels. Every image editor, every prepress system, every scientific imaging package and every ageing in-house tool has code for it, and that code has not needed to change in decades.

That is the whole argument for choosing it here. The reader of this page does not want TIFF’s layers, its multi-page support or its 32-bit depth; they want a file the program in front of them will not refuse. Uncompressed baseline is the safest bet on that, ahead of PNG on the very oldest software and comfortably ahead of anything newer.

The converter scans the CR3 for embedded JPEGs and keeps the largest one above 640 by 480, which on every EOS R body is a full-resolution rendering the camera produced when the shutter fired. That picture is decoded and written into the TIFF.

What stays behind is the part that made the file large: 14-bit sensor readings on a Bayer grid, which is what a raw developer works with. The latitude to recover a blown highlight or lift two stops of shadow is in that data and is not in an eight-bit camera rendering. So the TIFF is a faithful, uncompressed copy of a picture that has already been developed once, by the camera, with no way back.

Four bytes a pixel with no compression. An EOS R6 at 5,472 by 3,648 produces about 80 MB; an R5 at 8,192 by 5,464 produces about 179 MB; an R8 or R6 Mark II sits near the smaller figure and an R5 Mark II near the larger.

This is worth pausing over given who this page is for. Software old enough not to know about CR3 is also software written when 179 MB was an unusual amount of memory to hand a single document, and 32-bit applications in particular can fail on files that size in ways that are not always graceful. If the destination is genuinely old, set a maximum width during the conversion and give it something it can cope with.

The TIFF is written with four samples per pixel — red, green, blue and an alpha channel — with the ExtraSamples tag set to declare what the fourth one is. A photograph from a camera is entirely opaque, so that channel is 255 everywhere and takes up a quarter of the file to say nothing.

Well-behaved readers consult ExtraSamples and handle it without comment. A small number of older or narrower ones assume three samples and either refuse the file or show it oddly. If that happens, opening the TIFF in any editor and flattening it to RGB without alpha resolves it in seconds, and it is worth knowing that the problem is the reader rather than the file.

A TIFF can carry 16 bits per channel and prepress workflows routinely use that. This one carries eight, and not because of a limitation in the writer — the embedded preview inside a CR3 is an eight-bit JPEG, so eight bits is all there is to write.

The practical consequence is about what happens after the file is opened. Eight bits is ample for viewing, printing and light adjustment. It is thin for heavy tonal work: pulling a sky down or a shadow up by a stop or more will show banding that a 16-bit file absorbs. If the person receiving this TIFF is going to grade it hard, they need a real development of the CR3, not this.

The picture is decoded to pixels and encoded again, so the EXIF does not travel. Camera model, lens, focal length, aperture, shutter speed, ISO, capture time and any GPS coordinate are all absent from the TIFF, even though the format has a defined place for every one of them.

On a work machine handling other people’s pictures that is usually welcome — a property or site photograph no longer carries the coordinates of the address. Where it is not welcome is any workflow that files images by capture date. Keep the CR3 files as the record, since they hold all of it, and treat the TIFF as the copy the software can open.

The output carries no colour profile, so whatever opens it will assume sRGB. If the body was set to Adobe RGB — a setting people change once and never revisit — the preview inside the CR3 describes Adobe RGB colours and they will be interpreted as smaller, flatter sRGB ones.

The symptom is muted saturated colour rather than anything obviously broken, which is what makes it easy to miss until a print comes back. If colour accuracy is part of the job, check the camera’s colour space menu, and prefer a proper development in colour-managed software for anything where the difference would be noticed.

This is the situation the page is really for. Canon’s Digital Photo Professional is free and would do a better job, and on a managed laptop you cannot install it. Uploading client or patient images to an unknown converter is equally out of the question, and often explicitly forbidden.

Everything here runs in the tab: the file is read from disk by the page, scanned for its preview, decoded and written back out. No installer, no administrator prompt, no account, and no request carrying the image — which the network tab will show you, and a disconnected machine will prove.

Whole selections can be dropped at once, each converted separately with its own progress and taken together as a ZIP. Input files are accepted up to 100 MB, which every CR3 clears — a 45-megapixel frame is around 45 MB, or half that with Canon’s compressed raw option.

Before converting a large set, ask whether the software really needs an uncompressed file. If it will accept a JPG, that route hands over the camera’s embedded JPEG untouched, with no decode and no re-encode, at roughly one per cent of the size. TIFF earns its place when the picture is going to be edited and resaved inside the old program repeatedly, and the JPG route earns its place the rest of the time.