GIMP - for Mac OS X: "X Windowing Layer
GIMP uses a separate windowing layer, the X11 windowing protocol, on Mac OS X, which must be installed first. The XQuartz project provides this functionality. There you can download the most recent version of X11.app.
Graphics libraries and toolkits
Unlike most GNU/Linux distributions, Mac OS X does not come with the open source libraries upon which GIMP is built. These are typically installed along with GIMP, but can be installed separately. If you want to compile GIMP from source, we suggest that you use MacPorts or fink to install the libraries it depends on.
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