What Is a CRW File? Canon's First Raw Format, and the Two Things Everybody Gets Wrong
A CRW file is a raw photo from an early Canon camera. Jump to your question below, or read it through in order.
A CRW file is a raw photo from an early Canon camera. Jump to your question below, or read it through in order.
A CRW file is a raw photo from an early Canon camera. Canon wrote CRW from 2000 until 2004, then replaced it with CR2.
Two things about CRW get repeated everywhere and both are wrong. It is not uncompressed, and it is not undocumented. Canon published its container specification in 1997.
Shoot raw on an early Canon and your camera skips the step where it decides how that photo should look. No sharpening, no contrast curve, no white balance applied. What reaches your card is what every photosite measured, with settings recorded alongside as notes.
Photographers call that a digital negative. A negative is not the print. It holds more, and something has to develop it.
That is what a raw image format buys you. Every adjustment stays available in post-processing, where a JPEG has already had those adjustments applied and cannot give them back.
CRW is chapter one of three. Canon wrote CRW from 2000, CR2 from 2004 and CR3 since 2018. All three are called Canon raw and no two are the same format inside.
.crwHEAPCCDR at offset 6.thm, a JPEG thumbnailRaw means unprocessed. One brightness number per photosite, laid out in the Bayer mosaic your sensor uses, squeezed down by a compression step that throws nothing away. Color arrives later, from demosaicing at development rather than from your file.
Beside it sit the shot settings, the lens, the firmware version and a full table of white balance levels. Photographers call that metadata, and it travels with your picture.
A JPEG preview sits inside as well, which is how browsers show pictures of photos they cannot develop. Section 4 takes one apart.
Four Canon DSLRs and about a dozen PowerShots, between 2000 and 2004. EOS D30, D60, 10D and 300D, plus PowerShot G and S series bodies and the Pro1.
CRW covers a narrow slice of Canon history, and early Canon digital cameras are what most people are holding when they land here. Shoeboxes of files from a first digital camera, or hard drives inherited from somebody who bought one.
| Line | Bodies | Years |
|---|---|---|
| EOS DSLR | D30, D60, 10D, 300D Digital Rebel | 2000 to 2003 |
| PowerShot G | G1, G2, G3, G5, G6 | 2000 to 2004 |
| PowerShot S | S30, S40, S45, S50, S60, S70 | 2001 to 2004 |
| PowerShot Pro | Pro1 | 2004 |
The EOS D30 opened it. Canon announced that body on 17 May 2000 and it was the first digital SLR the company built itself, after years of rebadging Kodak. CMOS, 3.1 megapixels and raw files nobody could open yet.
There is no G4. Canon went G3, then G5, because four is an unlucky number in Japan. Any camera list reading “G1 to G6” is promising you a PowerShot that never existed.
Not sure which yours is? Look at the extension on the card. That is your entire test, and it beats any list, because Canon shipped bodies either side of 2004 in one year.
PowerShot raw ends with the G6 in 2004. Canon then shipped the G7 in 2006 with no raw mode at all, the only camera in that entire line without one. It took heavy criticism for that. Raw came back on the G9 in 2007, by then written as CR2.
CRW and CR2 share a maker and almost nothing else. CRW is built on Canon's CIFF, where data comes first and directories sit at the end. CR2 is built on TIFF, which works the other way round.
In 2004 Canon switched containers. The EOS 20D and 350D arrived writing CR2, built on TIFF. That ended CRW. In 2018 it happened again, and CR3 arrived built on a container family shared with MP4.
Built on CIFF. Canon's own container, published in 1997. Data first, directory last, offsets relative. Lossless Huffman compression.
Built on TIFF. Four directories, three of them previews. Lossless JPEG on the sensor data, and no published specification.
| Question | CRW | CR2 | CR3 |
|---|---|---|---|
| Container | CIFF, not TIFF | TIFF | ISO base media |
| Years | 2000 to 2004 | 2004 to 2018 | 2018 onward |
| Published spec | Yes, 1997 | No | No |
| Directory sits | At the end | Near the front | Either |
| Compression | Lossless Huffman | Lossless JPEG | Canon crx |
CIFF was superseded rather than extended. Read about its successor in what a CR2 file is, which covers the same ground for 2004 onward.
Check the extension before you blame your software. Folders out of old camera bags often hold both, because people upgraded mid-collection. Photos that will not open in software handling everything else in that folder are very often the other format, sitting quietly among them.
CIFF is Camera Image File Format, the container CRW sits in. Canon released it on 12 February 1997 and published the specification, which is why free software has read CRW reliably for twenty years.
Canon invented no container for CRW. It built one first, then used it. CIFF arrived in February 1997, developed with a group Canon called the CIFF Forum. Its specification went out in two documents rather than staying inside the company.
| Document | Version | Date |
|---|---|---|
| CIFF itself | Released | 12 February 1997 |
| Image Data File | 1.0 revision 4 | 24 December 1997 |
| File and Directory Organization | 1.0 revision 3 | 9 February 1998 |
That is the fact almost nobody repeats. Every page describing CRW calls the format proprietary and leaves it there. Proprietary and secret are different: Canon owns CIFF and Canon also told everybody how it works.
The Canon CRW file format is a joy to work with. It has a structure that is fundamentally similar to TIFF, with directories that point to data within the file. But a major improvement over TIFF is that the offsets are not absolute, they are relative to the start of the data block for each directory.
In a CRW the data comes before the directories, the reverse of TIFF and of EXIF. Open a TIFF and its map comes first. Open a CRW and that map comes last.
Its root directory begins 26 bytes in and runs to the end of the file. Those final four bytes tell a reader where entries start inside that block.
So software reads that tail, finds its directory, then jumps back into the data. Odd on paper, sensible in a camera: writing data before an index means your camera can stream a photo to the card without holding it all in memory.
Relative offsets are why CRW survives editing. Every entry counts from its own block rather than from byte zero, so software can copy an entire block elsewhere without recalculating anything. Phil Harvey's verdict: rewriting a CRW is “about 20 times easier, and much less prone to errors than rewriting a TIFF or JPEG”.
That same structure has a second job. Canon uses the HEAPJPGM signature to put CIFF blocks inside APP0 in an ordinary JPEG, so PowerShot JPEGs from those years carry the same metadata as raws beside them.
CRW files are compressed. Lossless Huffman coding, in every CRW ever written. Nothing is thrown away, which is what lossless means, but the data is squeezed all the same.
Search for CRW and you will be told, over and over, that the format stores uncompressed image data. The pages ranking first and second say so. An older version of this page said so twice.
It is wrong, and CRW files prove it three times over.
| Tag | Name | What it means |
|---|---|---|
0x1835 | DecoderTable | Sixteen bytes of raw decoder table. Nothing needs decoding unless it was encoded |
0x1803 | ImageFormat | The format number, then a target compression ratio |
0x2005 | RawData | The sensor data, the bulk of the file, sitting behind that decoder |
Lossless Huffman coding does the work, from the same family of trick that packs a ZIP archive. Values turning up often get short codes while rare ones get long codes, and every original number comes back exactly.
Lossless describes what survives. Uncompressed describes how much room it takes. A CRW keeps every measurement your sensor made and still fits in roughly half the space those measurements need written out plainly.
CR2 does the same, with lossless JPEG in place of Huffman. Canon has never shipped a raw format that stores sensor data plainly.
Why this mistake spreads. Raw images are larger than compressed formats like JPEG, and large feels like uncompressed. A CRW dwarfs the JPEG beside it because of bit depth and because no color shortcut is taken, not because compression is missing.
Compare that with the CR2 format, where an identical claim turns up on identical pages.
Free software is the best answer here, not Canon's. darktable and RawTherapee both read CRW, cost nothing and run everywhere. Canon's own Digital Photo Professional only handles CRW from selected models.
Programs that open CRW files split into two kinds, because two jobs need different tools. Seeing your photo is one. Developing it, which means choosing white balance and exposure your camera left open, is the other.
.jpg and anything will show it. See section 8.| Software | Cost | Why choose it |
|---|---|---|
| darktable | Free, open source | The safe first try. Windows, macOS and Linux, and it stays compatible with older cameras longer than most |
| RawTherapee | Free, open source | Strong Canon demosaicing, and more control than most people need |
| Adobe DNG Converter | Free | Converts rather than develops. Turns a CRW into a DNG anything can read |
| Lightroom, Adobe Photoshop | Subscription | Camera Raw still reads CRW, twenty years on |
| Canon Digital Photo Professional | Free from Canon | Handles selected models only, so try it second rather than first |
| IrfanView, ImageMagick | Free | Fast batch conversion when you have hundreds of files |
| ACDSee, Photoshop Elements | Paid | Photo managers that read CRW alongside everything else |
Under darktable, RawTherapee, GIMP and dozens of smaller tools sits one engine called LibRaw, and underneath that sits the decoding work published years ago. That shared foundation is why CRW support has aged better than those cameras did.
Two names on old lists are gone. Google discontinued Picasa in 2016, and Canon ZoomBrowser EX is no longer available either. The older version of this page recommended Picasa twice.
It also listed CorelDRAW, which draws vectors and has never opened a raw photo.
Searching for a free CRW viewer is riskier than it looks. Photo data cannot run anything, but download sites at the top of those searches bundle adware. Use the Microsoft Store, darktable.org, rawtherapee.com or Adobe's own site.
The usual cause is backwards from what people expect. Your software is too new, not too old, because support for twenty-year-old Canon bodies gets quietly dropped.
With most formats, files refuse to open because your software predates them. CRW inverts that, and the software that was compatible ten years ago may not be now. These cameras stopped selling twenty years ago, and every major rewrite since has been a chance to drop them.
Canon itself shows this pattern. Digital Photo Professional handles older CRW files from selected models only, which is a polite way of saying not all of them. An update makes that worse rather than better.
| What you see | What it usually means | Start with |
|---|---|---|
| Not supported, or an unknown format | Software that dropped support for this camera model | darktable, which still reads them |
| Canon software refuses it | Digital Photo Professional covers selected models | darktable or RawTherapee |
| No thumbnails in File Explorer | Raw Image Extension is not installed | The Microsoft Store, free |
| Opens small and flat | You are looking at the embedded preview | A developer that reads the raw block |
| Looks gray beside the JPEG | Nothing is wrong. Raw arrives undeveloped | Any raw developer |
| Nothing opens it at all | A part copy, or a bad card transfer | Section 10, then the memory card |
Digitising an old shoebox? Convert to DNG as you go. Support for these bodies is volunteer-maintained now, and the direction of travel is one way.
Something always gets the picture out. Develop in darktable, export a TIFF, then carry on in whatever you normally use. It costs one extra step and nothing else.
A THM file holds your photo as a JPEG thumbnail, written by the camera under the same name. Your CRW records that filename in a tag of its own, ThumbnailFileName, so the sidecar is named inside the raw file.
Open a folder off an old Canon card and the files arrive in pairs. CRW_1834.CRW next to CRW_1834.THM, over and over. That second file is a small JPEG of your photo, written so cameras could show you a picture on screen without decoding raw data first.
.jpg. It opens in anything. Small, already developed by your camera and fine for working out which files are worth keeping.0x0817, so that pairing is recorded rather than guessed.A CRW carries an embedded JPEG as well, separate from that THM and much larger. On a 300D it runs 2048 by 1360, usable in its own right and the reason damaged CRW files are often not a total loss.
THM is not a Canon-only extension. Camcorders and other cameras have used it for thumbnails too, so stray THM files with no raw beside them may have come from somewhere else entirely.
Develop first, export second. JPEG suits sharing, TIFF suits further editing and DNG suits archiving. Keep the CRW whatever you export, because the export cannot be undone.
Converting raw is really development. You choose the white balance, exposure and contrast your camera left open, then write that result somewhere ordinary.
| Export to | Keeps | Best for |
|---|---|---|
| JPEG | 8 bits, lossy, small | Sending, posting, printing at a shop |
| Full-quality JPEG | Same 8 bits, less thrown away | Sharing images when file size hardly matters |
| TIFF | 16 bits, lossless, layers if you add them | More editing elsewhere |
| DNG | Everything. Still raw, still adjustable | Archiving. See what a DNG file is |
| PSD | Layers, masks, adjustment stacks | A Photoshop project |
Exports land as .jpg, .tif or .dng, under the same name in the same folder. Your CRW stays where it was.
CIFF is documented, which helps, but documentation does not maintain software. The bodies that wrote CRW left production two decades ago and support now rests on volunteers who own one.
DNG is published, current and read by everything that reads raw at all. A DNG copy of a photo from 2002 is far likelier to open in 2042 than the CRW beside it.
Exporting to JPEG is not backing up your raw photo. Every export is one interpretation, flattened to 8 bits, with your room to change your mind removed.
Delete your CRW and keep that JPEG, and you have thrown away a negative and kept one print.
Taking the photo further afterwards? Photoshop PSD documents are where a developed raw usually ends up once you start working in layers.
Where damage sits decides everything. A CRW keeps its directory at the end, so a part copy that lost its tail has lost the map. That embedded JPEG can often still be pulled out.
Most formats degrade from the back. A truncated TIFF costs you the bottom of your picture and nothing more. CRW behaves differently, because its directory sits in that last chunk and describes everything else.
Lose the tail of a CRW and photo data may be entirely intact with nothing left to describe it. Lose the front and its header is gone while sensor data survives.
| Damage | What it costs | What is left |
|---|---|---|
| Truncated, tail missing | The directory, so nothing can be located | Sensor data and the embedded JPEG, both findable by hand |
| First bytes overwritten | The header and signature | Almost everything. A reader just needs telling what it is |
| A block in the middle | One record, often metadata | Usually the photo. Relative offsets keep the rest readable |
| Zero bytes throughout | Everything | Nothing. A failed card transfer rather than a damaged file |
Photos still on the original card? Copy the entire card to a drive before opening anything. CompactFlash cards from 2003 are past any sensible lifespan, and reading one repeatedly is how they fail.
Nothing in a CRW header is a checksum, so a damaged file looks perfectly normal in a folder listing until something tries to read it. Relative offsets help once you are in there.
A reader that finds one intact block can make sense of it without the rest, because nothing in that block depends on where it sits. That is unusual, and it is why hand recovery of a CRW works more often than it should.
Twenty-six bytes of header, then data, then a directory. Its signature is HEAPCCDR at offset 6, and the last four bytes point back at that entry list.
Nothing here helps you open a photo. It is on record for two reasons. CRW is the one Canon raw format whose details came from a published specification rather than from somebody taking files apart. And an older version of this page filled its specification table with software names instead.
| Property | Value |
|---|---|
| Full name | Canon Raw, listed by directories as a Canon Raw CIFF Image File |
| Category | Camera raw, a raw image format |
| Kind | A binary image file format, never text |
| Published specification | Yes. CIFF, released 12 February 1997 |
| Container | CIFF, little-endian |
| Signature | HEAPCCDR at offset 6, eight bytes |
| Version | 0x00010002, which reads as 1.2 |
| Header length | 26 bytes, recorded at offset 2 |
| Directory | At the end, pointed to by the final four bytes |
| Compression | Lossless Huffman on the sensor data |
| Color layout | Bayer mosaic |
| Media type | None registered with IANA. No Canon entry appears in the registry |
| Quoted in the wild | MIME image/x-canon-crw, unregistered. That x- prefix marks a type nobody registered |
Twenty-six bytes sit at the front of every CRW file, and half of them are signature and version.
| Offset | Bytes | What it means |
|---|---|---|
| 0 | II | Byte order, Intel little-endian |
| 2 | 1A 00 00 00 | Header length 0x0000001a, which is 26 bytes |
| 6 | HEAPCCDR | The signature that says Canon raw |
| 14 | 02 00 01 00 | CRW version 1.2, major 1 and minor 2 |
| 18 | Eight zero bytes | Reserved, two 32-bit integers |
That same eight-character trick appears in ordinary JPEGs from those cameras, where Canon writes HEAPJPGM into the APP0 segment and stores identical metadata blocks there.
Every entry is a 10-byte record: a tag, a size and an offset. That tag splits into three parts, which is neater than it sounds. Two bits say where its value lives, three bits say what kind of data it is and eleven bits identify it.
Anything shorter than eight bytes is stored inside its entry rather than out in the data block, so a shutter setting costs no extra space. Longer records sit in the data area, aligned on an even byte and padded with a zero when the length is odd.
The pointer at the very end is called DirStart, and a value block can hold a complete subdirectory with the same layout again, nested as deep as Canon needed.
Canon left itself room and then used it. Digital Photo Professional writes its edit recipes into spare space in that root directory block as VRD data, and VRD supports embedded XMP. That is how modern metadata ends up inside a file format from 1997.
Two questions sort out most of what is left. Answer them in order.
Do that first. It is free, it still reads these cameras and it ends most CRW problems on its own. See section 6.
Then you have a picture already. Copy it, rename that copy to .jpg and look. Section 8 explains the pair.
Sorting out a folder of camera files? Canon raw after 2004 covers the format that replaced this one, and Adobe DNG files are where old photos belong for the long term.
Shooting more than one brand? Sony ARW photo files, Nikon NEF raw photos and Fujifilm's RAF format work the same way and need the same care.
Editing what comes out? PSD files from Photoshop hold your layers. PDF documents are where prints and proofs end up, and TGA image files or PCX picture files turn up in archives from the same era.
Stuck on your computer rather than your photo? Our Windows fixes and macOS guides cover the system side.
New to all of this? What a file format is covers the ground underneath, and our file format guides list the rest.
Found something here that does not match your own file? Send us the exact wording on screen and we will check it against the specification.