It seems that many or most "raw" files output by digital cameras are some kind of TIFF file. At least Canon cr2 files are a form of TIFF file. You might think that knowing this would solve all the problems, but alas the TIFF file format is a flexible and extensible thing and therein lies the rub. Any vendor can extend the format in ways that suit their purpose. Nonetheless understanding TIFF is a good starting point for understanding a Canon image file (which is my goal), so here we go:

TIFF was designed to be a platform and os independent graphics file format. TIFF stands for "Tagged Image File Format". It is a flexible and extendible format. It is possible to embed proprietary information blocks in a TIFF block without violating the format. Aldus and Microsoft "control" the specification, which is in the public domain.

Here are some links and resources (you can find many more via a simple google search):

• Unofficial TIFF Home Page
• a TIFF FAQ
• TIFF page at faqs.org
• TIFF page at fileformat.info

• TIFF specification version 4.0
• TIFF specification version 5.0
• TIFF specification version 6.0 (postscript)

A TIFF file has 3 major components:

• The image file header (IFH) 8 bytes at offset zero.
• One or more image file directories (IFD) 8 bytes at offset zero.
• Directory entries (DE) which are held in the IFD.

The IFH (image file header) consists of 8 bytes:

• A 2 byte ordering field is MM (4D4D) for big endian, II (4949) for little endian (Intel) data. This pertains to all 16 bit or 32 bit data which follows the header.
• A 2 byte version field (always decimal 42 = 0x2a)
• A 4 byte offset to the IFD.

A tiff file can contain several IFD's if it contains several images. The IFD consists of a 2 byte count of directory entries, followed by the entries themselves (each 12 bytes), then another 4 byte offset to another IFD (or zero if this is the last IFD).

A DE is 12 bytes and consists of 4 fields. The first field is a tag, and this is the central concept in a TIFF file. Any unrecognized tags can and should be ignored and new tags can be added at any time. Tags with values from 32768 to 65355 are reserved for proprietary information. 45 tags were defined by the TIFF 5.0 specification. Here is a DE for you:

• 2 byte tag
• 2 byte type
• 4 byte length
• 4 byte value/offset