EXIF (Exchangable Image File) is part of the DCF (Digital Camera Filesystem) standard. The DCF was suggested to allow the exchange of information between digital cameras. Putting a Compact Flash card that has been used in a Nikon into a Canon digital camera, for example, should allow you to view the pictures. An extension of this is the print format that is bult into DCF: It allows you to mark pictures for print (and how many copies you want), so you - in theory - can pop the card into a printer or a print service, and get your prints, without needing a computer.
The EXIF standard itself was suggested by Japan Electronic Industry Development Association (JEIDA) in 1996, and was updated to version 2 in 1998. There has been talk of a revision into version 3, but there seems to be little support in the digital camera industry to implement another change, as the current EXIF format seems to do more than people need.
For most people, the pictures coming out of a digital camera are regular jpg or tiff (or RAW, as the case may be, but that is a different case altogether) files. However, the jpegs also contain so-called EXIF data.
This exif data can contain (among other things) any of the following:
- An audio clip (for notations)
- A compressed JPG thumbnail (for faster in-camera browsing)
- Picture-taking condition tags
- Colour space information (RGB, sRGB etc)
The need for an audio clip eludes me, apart from the fact it might be handy to take a note of the names of the people in the picture (in which case a pen and paper seems more useful, and doesn't take nearly as much space on the memory card).
The thumbnail file is particularly useful, especially as cameras get higher and higher resolutions. Imagine on the newer digital SLR cameras, where the files are often 20 MB+ (in RAW format). Reading all of this just to show a small image on the LCD on the camera is a waste of time and battery power. A separate JPG, in the correct resolution for the LCD screen, makes perfect sense.
The most important thing to consumers who are interested in becoming better photographers, however, is point #3: The picture taking condition tags. These tags contain the information about what the camera did when taking the image.
The image tags that are predefined by the EXIF standard include:
It can also store vendor- or camera-specific information.
The DCF and EXIF white papers, of which I unfortunately only have hard copies. I am sure they are available on the net as well, if you are interested in more information. (update: They were. See www.exif.org, although they don't have the newest version)