Canon RAW 2
Formats used by Canon cameras include:
Contents |
CRW
CRW, aka Camera Image File Format is an attempt by Canon to standardise camera files.
CR2
Canon RAW 2 (CR2) came to replace CRW, starting the 20D, 350D/Digital Rebel Xt and 1D.
Organization
Canon CR2 files are TIFF files. All is organised in a TIFF / IFD file.
On of the differenciation with the CR2 files is that they have a header before the IFD0. This does not violate the TIFF spec.
| offset | length | description |
|---|---|---|
| 0 | 8 | TIFF header |
| 8 | 2 | litteral 'CR' |
| 10 | 1 | major version (2) |
| 11 | 1 | minor version (0) |
| 12 | 4 | (long) for the offset of the IFD3 that contain the RAW data. (in the TIFF byte order) |
Exif is attached to the ExifIFD of IFD0. The CFA data is in IFD3.
Compression
Canon CR2 files use the old original Lossless JPEG standard for the RAW data. The same used by Adobe DNG.
Source: http://www.adobeforums.com/cgi-bin/webx/.3bc36454/0 (link dead)
The width dimension specified in the JPEG stream is actually half the reality because it takes into account 2 channels per sample (the dimension of the CFA pattern).
350D, 5D and 30D files have a different layout. IFD3 (where the CFA is located) has the tag 0xc640 that contains 3 SHORT. 1, x, y. x is the number of column of the first "slice" of the image, y is for the second "slice". I don't know what the 1 mean.
The slicing means that the output scanlines have to be reorganised as they are shorter to have a top -> bottom then left -> right, a bit like columns of text. (TODO: do a nice diagram)
Modified files
Apparently Canon's proprietary software modifies the RAW file. Other proprietary software seems to choke on said modified files (http://www.prophotohome.com/forum/raw-photo-processing-software-technique/62864-cr2-raws-converted-dpp-wont-open-aperture.html).
ExifTool has some info:
References
- http://lclevy.free.fr/cr2/
- http://web.archive.org/web/20061125031802/http://crousseau.free.fr/imgfmt_raw.htm (in French, by one of the developers of DxO) - Using the wayback machine !
