The EXIF digital camera file format

Olympus C-3000Z

A picture file from a modern digital camera contains more than just the image that the camera took. It can also contain:

A thumbnail version of the image
Date and time that the shot was taken
Original size of image
Details about the camera such as:
- Make
- Model
- Firmware revision
- Lens and flash options
- Owner's name
Photographic settings such as:

Automatic program mode in effect
F-stop
Exposure time
Aperture
White balance setting
Whether a flash was used

This meta-information is kept in the "Exchangeable Image File Format for Digital Still Cameras" (EXIF) header. This standard was developed by the Japan Electronic Industry Development Association (JEIDA) and observed by camera industry leaders such as Nikon, Canon, Kodak, Olympus, etc. A much more readable description is at TsuruZoh Tachibanaya's website which also includes MakerNote formats for various makes.

This header is stored in an "application segment" of a JPEG file, or as privately defined tags in a TIFF file. This means that the resulting JPEG or TIFF is still in a standard format readable by applications that are ignorant of EXIF information. Note that most such applications usually don't keep around anything that they don't understand, so if you edit the image, you will lose the EXIF information.

I wrote EXIF.py to extract this data into a Python dictionary suitable for use by image gallery programs and other such applications.

Understands the MakerNotes of several different camera makes. Supports all the formats documented on TsuruZoh Tachibanaya's page.
Currently implemented:
- Old-style Nikon (E700, E800, E900, E900S, E910, E950, etc.)
- New-style Nikon (E99x or D1)
- Olympus
- Casio (not tested - no sample image file)
- Canon (from David Burren's page)
- Fujifilm (Fuji Finepix)
Modular design makes it very easy to add MakerNote formats.
Reads JPEG, JFIF and TIFF format image files.
Can extract both JPEG format and TIFF format thumbnails. For example, the Kodak DC210 and Sony D700 write TIFF formatted thumbnails.
Can extract thumbnails (if present) from MakerNotes. For example, Olympus stores a JPEG thumbnail within the MakerNote in TIFF files.
Reads the GPS IFD, if present. (Not tested because I've seen no images with this yet)
Data structure preserves tags from all IFDs, even if they have the same name. (For instance, the thumbnail IFD shares tag names with the main image IFD.)
Data structure preserves raw tag information, as well as having the tag data nicely formatted for printing.
Tested on all the images on the exif.org sample image page.
Based on the excellent code in exifdump.py written by Thierry Bousch <bousch@topo.math.u-psud.fr> with updates to handle TIFFs and JFIF-format JPEGs, extract JPEG and TIFF thumbnails, and decode MakerNotes, and also factored into a library returning a more useful data structure.

There is only one public function:

process_file(file, debug=0)

where file is an open file like object that supports seek(), and debug is a flag that enables debugging output when true.

It returns a dictionary of EXIF tags found, keyed by tag name, and possibly a thumbnail. The entries are "IFD_Tag" objects.

Object Attributes	Meaning
printable	String representation of tag, suitable for printing.
tag	Numeric tag ID.
field_type	Index into the FIELD_TYPES list. Each FIELD_TYPES entry is a (length of type in bytes, type name abbreviation, type full name) tuple.
values	String or array of raw values from tag.
field_offset	Offset of start of tag from beginning of file. Used by MakerNote processing.

Tag names are prefixed with the name of the IFD, to prevent collisions between tags with the same name in different IFDs.

Example Code
exiftool is a example command-line tool using the above library. It can generate plain-text or HTML files from the EXIF information. It can extract the thumbnail (if any) to a separate file. It can also rename the files according to the EXIF creation date. This was inspired by the utility by Robert F. Tobler <rft@cg.tuwien.ac.at>.