xref: /third_party/libexif/README

				    libexif
				    -------

DESCRIPTION
-----------

libexif is a library for parsing, editing, and saving EXIF data. It is
intended to replace lots of redundant implementations in command-line
utilities and programs with GUIs.


FEATURES
--------

libexif supports parsing, editing and saving of EXIF data. In addition, it
has gettext support. All EXIF tags described in EXIF standard 2.1 (and most
from 2.2) are supported.  Many maker notes from Canon, Casio, Epson,
Fuji, Nikon, Olympus, Pentax and Sanyo cameras are also supported.


REQUIREMENTS
------------

libexif is written in plain C and does not require any additional library.
GNU gettext will be used for language translation, if available.


LIMITATIONS
-----------

libexif can only handle some maker notes, and even those not very well. More
work needs to be done. Note that libmnote has been merged with libexif - it
is no longer needed.


USAGE
-----

We have documented the libexif API using doxygen and are making
the results available at https://libexif.github.io/api/

The short test programs in the test directory illustrates how to create
valid EXIF data from scratch, how to save EXIF data and how to load EXIF
data from data in memory. To run the test programs, just run make check.
There are also a few simple example programs available in the
contrib/examples/ directory.  Don't hesitate to contact
us at <libexif-devel@lists.sourceforge.net> if you have any questions
on how to use libexif.

To link to libexif into your own package, we recommend using the
pkgconfig utility (cf. https://www.freedesktop.org/wiki/Software/pkg-config/ For
your convenience, libexif both provides libexif-uninstalled.pc and
installs libexif.pc.


FRONTENDS
---------

Here are a few frontends to libexif:
 - exif:     A small command-line utility to show EXIF information in JPEG
             files (https://github.com/libexif/libexif).
 - gexif:    A GTK+ frontend for editing EXIF data
             (https://github.com/libexif/gexif).
 - gphoto2:  A command-line frontend to libgphoto2, a library to access a
             wide range of digital cameras (http://www.gphoto.org).
 - gtkam:    A GTK+ frontend to libgphoto2 (http://www.gphoto.org).
 - thirdeye: Digital photos organizer and driver for eComStation
             (http://ecomstation.ru/thirdeye).
 - digikam:  digital photo management application for KDE
             (https://www.digikam.org/)

If you would like to migrate your program to use libexif or add EXIF support
to it, don't hesitate to contact the authors.


LIBRARIES
---------

The following libraries use or have been inspired by libexif:
 - libexif-gtk: library of widgets to help display EXIF tags in GTK
   programs (https://github.com/libexif/libexif-gtk).
 - pel: PHP-Code (https://github.com/lsolesen/pel/)


BUILDING
--------

It really depends on your environment what to do in order to get libexif
to build. Building from the source tar ball usually involves the commands:

  ./configure
  make
  sudo make install

When building from source out of git, something like the following will be
necessary:

  autoreconf -i
  ./configure
  make

Besides the standard arguments, configure takes several specific to libexif:

  --disable-docs          To disable producing any documentation
  --enable-internal-docs  Build internal code docs if Doxygen available
  --enable-ship-binaries  To include Windows DLLs in 'make dist'

Certain specialized applications can reduce the size of the libexif
binary by setting one or both of the following macros in the CPPFLAGS
environment variable at configure time.  Each one removes certain kinds of
text strings and constants from the binary.  Applications which need
to access specific, known EXIF tags and know in advance the meaning of
their data have no need of those strings and can save considerable space
by eliminating them.

 -DNO_VERBOSE_TAG_STRINGS Names and descriptions of EXIF tags, debug messages,
                          mandatory EXIF fields (disabling auto-tag-fixup)
 -DNO_VERBOSE_TAG_DATA    Names of enumerated tag data contents


INTERNATIONALIZATION
--------------------

The libexif translations are made by volunteers working on their own,
either directly with the libexif project or through one of two translation
coordination sites, the Translation Project
<https://translationproject.org/domain/libexif.html> and Launchpad
<https://translations.edge.launchpad.net/ubuntu/bionic/+source/libexif/+pots/libexif-12>.
Any updates to language translations coordinated by the Translation Project
must be made through their web site, but all other languages can be
updated either through Launchpad (preferred) or by sending updates to
the libexif developers mailing list directly.  As of this writing, the
following languages must be updated through the Translation Project:
cs da de es fr it ja nl pl pt sk sv uk vi

If you are interested in translating libexif into a new language, we
recommend that you join one of the above translation groups and take
advantage of the systems they have built to help you.  A translation
disclaimer is NOT required for libexif at the Translation Project; by making
a translation, you agree implicitly to provide it under the same license
terms as the rest of libexif (LGPL).


AUTHORS
-------

libexif has originally been written by Curtis Galloway
<curtisg@users.sourceforge.net>. Because of the original design not
supporting editing and saving, Lutz Mueller <lutz@users.sourceforge.net>
rewrote libexif from scratch. Since then, many more people have contributed
to libexif.


LINKS
-----

Some links you might want to check out if you are interested in further
information about EXIF.

 - https://drewnoakes.com/code/exif: metadata extraction framework in Java
 - https://www.exif.org: information about the EXIF standard.
 - https://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/index.html: Looks
   like libexif in Perl. Seems to support a lot of MakerNotes.