CR2 files are generated by Canon cameras, starting the 20D, 350D/Digital Rebel Xt and 1D. They supersede the older [[Canon CRW|CRW]]. 


# MIME type

image/x-canon-cr2 
# Organisation

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.  
[[!table header="no" class="mointable" data="""
 **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|Lossless_JPEG]] standard for the RAW data. The same used by [[Adobe DNG|Adobe DNG]]. 

Source: [[http://www.adobeforums.com/cgi-bin/webx/.3bc36454/0|http://www.adobeforums.com/cgi-bin/webx/.3bc36454/0]] (Dead link) 

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|http://www.prophotohome.com/forum/raw-photo-processing-software-technique/62864-cr2-raws-converted-dpp-wont-open-aperture.html]]). 

[[ExifTool|ExifTool]] has some info: 

* [[http://www.cpanforum.com/threads/1055|http://www.cpanforum.com/threads/1055]] 
* [[http://www.cpanforum.com/threads/5170|http://www.cpanforum.com/threads/5170]] 

# References

* [[http://lclevy.free.fr/cr2/|http://lclevy.free.fr/cr2/]] 
* [[http://web.archive.org/web/20061125031802/http://crousseau.free.fr/imgfmt_raw.htm|http://web.archive.org/web/20061125031802/http://crousseau.free.fr/imgfmt_raw.htm]] (in French, by one of the developers of DxO)