One of the nicest things about GIMP is how easily its
functionality can be extended, by using plugins.
GIMP plugins are external programs that run under the
control of the main GIMP application and interact
with it very closely. Plugins can manipulate images in almost any way
that users can. Their advantage is that it is much easier to add a
capability to GIMP by writing a small plugin than by
modifying the huge mass of complex code that makes up the
GIMP core. Many valuable plugins have C source code
that only comes to 100-200 lines or so.
Several dozen plugins are included in the main GIMP
distribution, and installed automatically along with
GIMP. Most of them can be accessed through the
Filters menu (in fact, everything in that menu is a
plugin), but a number are located in other menus. In many cases you can
use one without ever realizing that it is a plugin: for example, the
"Normalize" function for automatic color correction is actually a
plugin, although there is nothing about the way it works that would tell
In addition to the plugins included with GIMP, many
more are available on the net. A large number can be found at the
Registry, a web site whose purpose is to provide a central
repository for plugins. Creators of plugins can upload them there;
users in search of plugins for a specific purpose can search the site in
a variety of ways.
Anybody in the world can write a GIMP plugin and make
it available over the web, either via the Registry or a personal web
site, and many very valuable plugins can be obtained in this way some
are described elsewhere in the User's Manual. With this freedom from
constraint comes a certain degree of risk, though: the fact that anybody
can do it means that there is no effective quality control. The plugins
distributed with GIMP have all been tested and tuned
by the developers, but many that you can download were just hacked
together in a few hours and then tossed to the winds. Some plugin
creators just don't care about robustness, and even for those who do,
their ability to test on a variety of systems in a variety of situations
is often quite limited. Basically, when you download a plugin, you are
getting something for free, and sometimes you get exactly what you pay
for. This is not said in an attempt to discourage you, just to make sure
you understand reality.
Plugins, being full-fledged executable programs, can do any of the
things that any other program can do, including install back-doors on
your system or otherwise compromise its security. Don't install a
plugin unless it comes from a trusted source.
These caveats apply as much to the Plugin Registry as to any other
source of plugins. The Registry is available to any plugin creator who
wants to use it: there is no systematic oversight. Obviously if the
maintainers became aware that something evil was there, they would
remove it. (That hasn't happened yet.) There is, however, for
GIMP and its plugins the same warranty as for any
other free software: namely, none.
Plugins have been a feature of GIMP for many
versions. However, plugins written for one version of
GIMP can hardly ever be used successfully with
other versions. They need to be ported: sometimes this is easy,
sometimes not. Many plugins are already available in several
versions. Bottom line: before trying to install a plugin, make sure
that it is written for your version of GIMP.
For the most part you can use a plugin like any other
GIMP tool, without needing to be aware that it is a
plugin. But there are a few things about plugins that are useful to
One is that plugins are generally not as robust as the
GIMP core. When GIMP crashes, it
is considered a very serious thing: it can cost the user a lot of
trouble and headache. When a plugin crashes, the consequences are
usually not so serious. In most cases you can just continuing working
without worrying about it.
Because plugins are separate programs, they communicate with the
GIMP core in a special way: The
GIMP developers call it “talking over a
wire”. When a plugin crashes, the communication breaks down,
and you will see an error message about a “wire read
When a plugin crashes, GIMP gives you a very
ominous-looking message telling you that the plugin may have left
GIMP in a corrupted state, and you should consider
saving your images and exiting. Strictly speaking, this is quite
correct, because plugins have the power to alter almost anything in
GIMP, but for practical purposes, experience has
shown that corruption is actually quite rare, and many users just
continue working and don't worry about it. Our advice is that you
simply think about how much trouble it would cause you if something
went wrong, and weigh it against the odds.
Because of the way plugins communicate with GIMP,
they do not have any mechanism for being informed about changes you make
to an image after the plugin has been started. If you start a plugin,
and then alter the image using some other tool, the plugin will often
crash, and when it doesn't will usually give a bogus result. You should
avoid running more than one plugin at a time on an image, and avoid
doing anything to the image until the plugin has finished working on it.
If you ignore this advice, not only will you probably screw up the
image, you will probably screw up the undo system as well, so that you
won't even be able to recover from your foolishness.
Installing New Plugins
The plugins that are distributed with GIMP don't
require any special installation. Plugins that you download yourself do.
There are several scenarios, depending on what OS you are using and how
the plugin is structured. In Linux it is usually pretty easy to install
a new plugin; in Windows, it is either easy or very hard. In any case,
the two are best considered separately.
Most plugins fall into two categories: small ones whose source
code is distributed as a single .c file, and larger ones whose
source code is distributed as a directory containing multiple
files including a Makefile.
For a simple one-file plugin, call it borker.c,
installing it is just a matter of running the command
gimptool-2.0 --install borker.c. This command
compiles the plugin and installs it in your personal plugin directory,
~/gimp-2.2/plugins unless you have changed it.
This will cause it to be loaded automatically the next time you start
GIMP. You don't need to be root to do these things;
in fact, you shouldn't be. If the plugin fails to compile, well, be
Once you have installed the plugin, how do you activate it?
The menu path is determined by the plugin itself, so to answer
this you need to either look at the documentation for the
plugin (if there is any), or launch the Plugin Description
dialog (from Xtns/Plugins Details) search the plug-in by
its name and look ot the Tree view tab.
If you still don't find, finally explore the menus or look
at the source code in the Register section -- whichever is easiest.
For more complex plugins, organized as a directory with multiple
files, there ought to be a file inside called either
INSTALL or README, with
instructions. If not, the best advice is to toss the plugin in the
trash and spend your time on something else: any code written with so
little concern for the user is likely to be frustrating in myriad
Some plugins (specifically those based on the GIMP
Plugin Template) are designed to be installed in the main system
GIMP directory, rather than your home directory.
For these, you will need to be root to perform the final stage of
installation (when issuing the make install
If you install in your personal plugin directory a plugin that has the
same name as one in the system plugin directory, only one can be
loaded, and it will be the one in your home directory. You will
receive messages telling you this each time you start
GIMP. This is probably a situation best avoided.
Windows is a much more problematic environment for building software
than Linux. Every decent Linux distribution comes fully supplied with
tools for compiling software, and they are all very similar in the way
they work, but Windows does not come with such tools. It is possible
to set up a good software-building environment in Windows, but it
requires either a substantial amount of money or a substantial amount
of effort and knowledge.
What this means in relation to GIMP plugins is the
following: either you have an environment in which you can build
software, or you don't. If you don't, then your best hope is to find a
precompiled version of the plugin somewhere (or persuade somebody to
compile it for you), in which case you simply need to put it into your
personal plugin directory. If you do have an environment in which you
can build software (which for present purposes means an environment in
which you can build GIMP), then you no doubt
already know quite a bit about these things, and just need to follow
the Linux instructions.
If you would like to set up a build environment, and are ready for the
heroism involved, you can find a reasonably recent description of how
to go about it in the GIMP Wiki, at
HowToCompileGimp/MicrosoftWindows . Since it is a Wiki,
anybody is free to edit it, so please keep it up to date by adding
advice based on your own experiences.
We could use some material here.
If you want to learn how to write a plugin, you can find plenty of help
at the GIMP Developers web site,
developer.gimp.org. GIMP is a complex
program, but the development team has made strenuous efforts to flatten
the learning curve for plugin writing: there are good instructions and
examples, and the main library that plugins use to interface with
GIMP (called “libgimp”) has a
well-documented API. Good programmers, learning by
modifying existing plugins, are often able to accomplish interesting
things after just a couple of days of work.