What is the CRW file format?
.crw is Canon's legacy proprietary camera raw image format, built on the CIFF (Camera Image File Format) specification co-developed with Kodak in December 1997. It stores unprocessed 12-bit Bayer-pattern sensor data captured directly by the image sensor, preserving full dynamic range before any in-camera JPEG processing is applied.
Unlike the later .cr2 format (which wraps raw data in a TIFF container) and .cr3 (ISO Base Media File Format), .crw uses the CIFF heap structure - directory entries store offsets relative to their own block rather than absolute file positions. The file begins with a distinctive 14-byte header: the little-endian marker II, a 4-byte CIFF block-size pointer, then the ASCII string HEAPCCDR - the heap identifier for "Camera Canon DR."
Each .crw file embeds a JPEG thumbnail alongside the raw sensor data and Canon-specific metadata (MakerNote). File sizes range from roughly 3 MB to 10 MB. The format was used in Canon cameras from the PowerShot G1 (September 2000) through the EOS D30, D60, 10D, and 300D (Digital Rebel) - the last cameras to write .crw. Canon switched to .cr2 with the EOS 20D in 2004.
Today, .crw files can be processed in Adobe Photoshop (via Camera Raw), darktable, RawTherapee, Canon Digital Photo Professional, and the Adobe DNG Converter. ExifTool by Phil Harvey is the authoritative open-source parser for the CIFF structure.
Security & safety
RISK: LOWCRW is a passive camera raw image file containing sensor data and metadata - no executable code. Opening one is safe. Metadata (EXIF) in CRW can include GPS coordinates, camera serial number, and timestamps - strip before publishing if privacy matters (ExifTool). The large file size (3-10 MB) means no practical risk from malformed files in production tools.
Format details
in a nutshellPrograms that open CRW files
Windows12 apps
Adobe Photoshop Lightroom
Paid Import CRW into Lightroom catalog for non-destructive editing and batch export. 
FastPictureViewer Professional
Paid Windows Explorer codec extension for fast CRW thumbnail preview; paid. 
darktable
Open-source Free raw developer; import CRW to edit non-destructively and export to JPG/TIFF. 
Adobe DNG Converter
Free Batch-convert CRW files to DNG (open archival raw format). Free standalone download. 
macOS3 apps
Canon Digital Photo Professional (DPP)
Free Canon's free raw developer for Mac; download from Canon support. Opens CRW natively.
Apple Photos / Preview
Built-in macOS has built-in Canon CRW support via Core Image RAW; double-click to preview. 
Linux2 apps
Technical details
deep spec| Container format | CIFF (Camera Image File Format) - Canon/Kodak proprietary; distinct from TIFF |
| Magic bytes | `49 49 1A 00 00 00 48 45 41 50 43 43 44 52` ("II" + CIFF block pointer + "HEAPCCDR") at offset 0 |
| Byte order | Little-endian ("II" marker at offset 0) |
| Raw bit depth | 12-bit per channel (Bayer CFA sensor data); 36-bit effective colour depth |
| Colour pattern | Bayer CFA (Color Filter Array) mosaic - demosaicing required to produce a viewable image |
| Compression | Lossless; raw sensor data stored with minimal processing |
| Embedded thumbnail | JPEG preview image stored as a record in the CIFF directory |
| Metadata | Canon MakerNote stored as a CIFF directory record alongside EXIF-equivalent fields |
| Directory structure | CIFF heap with CDir (chunk directory) at end of file; all offsets are relative to their own block, not absolute |
| Maximum resolution | ~6.3 MP (EOS 10D / EOS 300D Digital Rebel - the last Canon cameras to produce CRW files) |
| Compatible cameras | PowerShot G1-G5, Pro70, Pro90 IS, EOS D30, D60, 10D, 300D (Digital Rebel) |
| Superseded by | `.cr2` (TIFF-based Canon raw, introduced with EOS 20D, 2004) |
| Typical file size | 3 MB - 10 MB |
| Released | 1997 (CIFF spec); in cameras ~2000 (Canon G1, D30) |
| Latest version | CIFF v1.0 rev 4 (December 24, 1997) - format never updated; superseded by CR2 |
| Specification | exiftool.org |
CRW conversions
Community Q&A
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